Wednesday, November 30, 2005
Group A Streptococcal Infections
Group A streptococcal (strep) infections are caused by group A streptococcus, a bacterium responsible for a variety of health problems. These infections can range from a mild skin infection or sore throat to severe, life-threatening conditions such as toxic shock syndrome and necrotizing fasciitis, commonly known as flesh eating disease. Most people are familiar with strep throat, which along with minor skin infection, is the most common form of the disease. Health experts estimate that more than 10 million mild infections (throat and skin) like these occur every year.
In addition to step throat and superficial skin infections, group A strep bacteria can cause infections in tissues (group of cells joined together to perform the same function) at specific body sites, including lungs, bones, spinal cord, and abdomen.
STREP THROAT
Symptoms of strep throat
Your health care provider may call it acute streptococcal pharyngitis. If you have strep throat infection, you will have a red and painful sore throat and may have white patches on your tonsils. You also may have swollen lymph nodes in your neck, run a fever, and have a headache. Nausea, vomiting, and abdominal pain can occur but are more common in children than in adults.
Transmission of strep throat
You can get strep throat and other group A strep infections by direct contact with saliva or nasal discharge from an infected person. Most people do not get group A strep infections from casual contact with others, but a crowded environment like a dormitory, school, or an institutional setting such as a nursing home can make it easier for the bacteria to spread. There have also been reports of contaminated food, especially milk and milk products, causing infection. You can get sick within 3 days after being exposed to the germ. Once infected, you can pass the infection to others for up to 2 to 3 weeks even if you don’t have symptoms. After 24 hours of antibiotic treatment, you will no longer spread the germs to others.
Diagnosis of strep throat
Your health care provider will take a throat swab. This will be used for a culture (a type of laboratory test) or a rapid strep test, which only takes 10 to 20 minutes. If the result of the rapid test is negative, you may get a follow-up culture to confirm the results, which takes 24 to 48 hours. If the culture test is also negative, your health care provider may suspect you do not have strep, but rather another type of infection. The results of these throat cultures will affect what your health care provider decides to be the best treatment. Most sore throats are caused by viral infections, however, and antibiotics are useless against them.
Treatment for strep throat
If you have a strep infection, your health care provider will prescribe an antibiotic. This will help reduce symptoms, and after 24 hours of taking the medicine, you will no longer be able to spread the infection to others. Treatment will also reduce the chance of complications.
Health experts think penicillin is the best medicine for treating strep throat because it has been proven to be effective, safe, and inexpensive. Your health care provider may have you take pills for 10 days or give you a shot. If you are allergic to penicillin there are other antibiotics your health care provider can give you to clear up the illness.
During treatment, you may start to feel better within 4 days. This can happen even without treatment. Still, it is very important to finish all your medicine to prevent complications.
Children with strep throat are usually treated with amoxicillin.
Complications of strep throat
Untreated group A strep infection can result in rheumatic fever and post-streptococcal glomerulonephritis (PSGN). Rheumatic fever develops about 18 days after a bout of strep throat and causes joint pain and heart disease. It can be followed months later by Sydenham’s chorea, a disorder where the muscles of the torso and arms and legs are marked with dancing and jerky movements. PSGN is an inflammation of the kidneys that may follow an untreated strep throat but more often comes after a strep skin infection. Both disorders are rarely seen in the United States because of prompt and effective treatment of most cases of strep throat.
SKIN INFECTIONS: IMPETIGO, CELLULITIS, ERYSIPELAS
Impetigo
Impetigo is an infection of the top layers of the skin and is most common among children ages 2 to 6 years. It usually starts when the bacteria get into a cut, scratch, or insect bite. Impetigo is usually caused by staphylococcus (staph), a different bacterium, but can be caused by group A streptococcus. Skin infections are usually caused by different types (strains) of strep bacteria than those that cause strep throat. Therefore, the types of strep germs that cause impetigo are usually different from those that cause strep throat.
Symptoms of impetigo
Symptoms start with red or pimple-like lesions (sores) surrounded by reddened skin. These lesions can be anywhere on your body, but mostly on your face, arms, and legs. Lesions fill with pus, then break open after a few days and form a thick crust. Itching is common. Your health care provider can diagnose the infection by looking at the skin lesions.
Transmission of impetigo
The infection is spread by direct contact with wounds or sores or nasal discharge from an infected person. Scratching may spread the lesions. From the time of infection until you show symptoms is usually 1 to 3 days. If your skin doesn’t have breaks in it, you can’t be infected by dried streptococci in the air.
Treatment for impetigo
Your health care provider will prescribe oral antibiotics, as with strep throat. This treatment may also include an antibiotic ointment to be used on your skin.
Cellulitis and erysipelas
Cellulitis is inflammation of the skin and deep underlying tissues. Erysipelas is an inflammatory disease of the upper layers of the skin. Group A strep germs are the most common cause of both conditions.
Symptoms of cellulitis and erysipelas
Symptoms of cellulitis may include fever and chills and swollen “glands” or lymph nodes. Your skin will be painful, red, and tender. Your skin may blister and then scab over. You may also have perianal (around the anus) cellulitis may with itching and painful bowel movements.
With erysipelas, a fiery red rash with raised borders may occur on your face, arms, or legs. Your skin will be hot, red, and have sharply defined raised areas. The infection may come back, causing chronic swelling of your arms or legs (lymphedema).
Transmission of cellulitis or erysipelas
Both cellulitis and erysipelas begin with a minor incident, such as a bruise. They can also begin at the site of a burn, surgical cut, or wound, and usually affect your arm or leg. When the rash appears on your trunk, arms, or legs, however, it is usually at the site of a surgical cut or wound. Even if you have no symptoms, you carry the germs on your skin or in your nasal passages and can transmit the disease to others.
Diagnosis and treatment of cellulitis and erysipelas
Your health care provider may take a sample or culture from your skin lesions to identify the bacteria causing infection. He or she may also recover the bacteria from your blood. Depending on how severe the infection is, treatment involves either oral or intravenous (through the vein) antibiotics.
SCARLET FEVER
Scarlet fever is another form of group A strep disease that can follow strep throat. It is usually contagious and lasts for a specific length of time whether or not it is treated.
Symptoms of scarlet fever
In addition to the symptoms of strep throat, a red rash appears on the sides of your chest and abdomen. It may spread to cover most of your body. This rash appears as tiny, red pinpoints and has a rough texture like sandpaper. When pressed on, the rash loses color or turns white. There may also be dark red lines in the folds of skin. You may get a bright strawberry-red tongue and flushed (rosy) face, while the area around your mouth remains pale. The skin on the tips of your fingers and toes often peels after you get better. If you have a severe case, you may have a high fever, nausea, and vomiting.
Transmission of scarlet fever
You can get scarlet fever the same way as strep throat—through direct contact with throat mucus, nasal discharge, and saliva of an infected person.
Treatment for scarlet fever
Like strep throat, your health care provider will treat scarlet fever with antibiotics.
SEVERE STREP INFECTIONS
Some types of group A strep bacteria cause severe infections. These include
Bacteremia (blood stream infections)
Toxic shock syndrome (multi-organ infection)
Necrotizing fasciitis (flesh-eating disease)
In 2004, 3,833 cases of severe group A streptococcal disease were reported to the Centers for Disease Control and Prevention.
All severe group A strep infections may lead to shock, organ failure, and death. Health care providers must recognize and treat such infections quickly.
Health care providers diagnose these infections by looking at blood counts and doing urine tests as well as cultures of blood or fluid from a wound site.
Antibiotics used to treat these severe infections include penicillin, erythromycin, and clindamycin. If you have severe tissue damage, your health care provider may need to remove the tissue surgically or amputate the limb.
People at the greatest risk of getting a severe strep infection are
Children with chickenpox
People with suppressed immune systems
Burn victims
Elderly people with cellulitis, diabetes, blood vessel disease, or cancer
People taking steroid treatments or chemotherapy
Intravenous drug users
Severe group A strep disease may also occur in healthy people who have no known risk factors.
RESEARCH
Through research, health experts have learned that there are more than 120 different strains of group A streptococci, each producing its own unique proteins. Some of these proteins are responsible for specific group A streptococcal diseases.
With the support of the National Institute of Allergy and Infectious Diseases (NIAID), scientists have determined the genetic sequence, or DNA code, for five different strains of the group A streptococcus organism.
By studying an organism’s genes, scientists learn which proteins are responsible for virulence, crucial information that will lead to new and improved drugs and vaccines. NIAID funds are supporting research for developing a group A streptococcus vaccine and several candidate vaccines are in various phases of development.
As a result of NIAID-supported research, the first group A streptococci vaccine clinical trial in 30 years was conducted. The vaccine was well tolerated by patients and has led to further clinical evaluation of a similar vaccine candidate. An effective vaccine will prevent not only strep throat and impetigo but also more serious invasive disease and post-infectious complications like rheumatic fever. In addition, vaccine development efforts include NIAID support of epidemiological studies to determine the burden of group A streptococcal disease and
characterize group A streptococcal strains causing illness in the United States and developing countries.
MORE INFORMATION
National Library of National Institute of Neurological Disorders and Stroke P.O. Box 5801 Bethesda, MD 208241-800-352-9424
Group A Strep Infections
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Group A Streptococcal (GAS) Disease
What is group A streptococcus (GAS)?
Group A streptococcus is a bacterium often found in the throat and on the skin. People may carry group A streptococci in the throat or on the skin and have no symptoms of illness. Most GAS infections are relatively mild illnesses such as "strep throat," or impetigo. On rare occasions, these bacteria can cause other severe and even life-threatening diseases
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How are group A streptococci spread?
These bacteria are spread through direct contact with mucus from the nose or throat of persons who are infected or through contact with infected wounds or sores on the skin. Ill persons, such as those who have strep throat or skin infections, are most likely to spread the infection. Persons who carry the bacteria but have no symptoms are much less contagious. Treating an infected person with an antibiotic for 24 hours or longer generally eliminates their ability to spread the bacteria. However, it is important to complete the entire course of antibiotics as prescribed. It is not likely that household items like plates, cups, or toys spread these bacteria.
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What kind of illnesses are caused by group A streptococcal infection?
Infection with GAS can result in a range of symptoms:
No illness
Mild illness (strep throat or a skin infection such as impetigo)
Severe illness (necrotizing faciitis, streptococcal toxic shock syndrome)
Severe, sometimes life-threatening, GAS disease may occur when bacteria get into parts of the body where bacteria usually are not found, such as the blood, muscle, or the lungs. These infections are termed "invasive GAS disease." Two of the most severe, but least common, forms of invasive GAS disease are necrotizing fasciitis and Streptococcal Toxic Shock Syndrome. Necrotizing fasciitis (occasionally described by the media as "the flesh-eating bacteria") destroys muscles, fat, and skin tissue. Streptococcal toxic shock syndrome (STSS), causes blood pressure to drop rapidly and organs (e.g., kidney, liver, lungs) to fail. STSS is not the same as the "toxic shock syndrome" frequently associated with tampon usage. About 20% of patients with necrotizing fasciitis and more than half with STSS die. About 10%-15% of patients with other forms of invasive group A streptococcal disease die.
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How common is invasive group A streptococcal disease?
About 9,400 cases of invasive GAS disease occurred in the United States in 1999. Of these, about 300 were STSS and 600 were necrotizing fasciitis. In contrast, there are several million cases of strep throat and impetigo each year.
Why does invasive group A streptococcal disease occur?
Invasive GAS infections occur when the bacteria get past the defenses of the person who is infected. This may occur when a person has sores or other breaks in the skin that allow the bacteria to get into the tissue, or when the person’s ability to fight off the infection is decreased because of chronic illness or an illness that affects the immune system. Also, some virulent strains of GAS are more likely to cause severe disease than others.
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Who is most at risk of getting invasive group A streptococcal disease?
Few people who come in contact with GAS will develop invasive GAS disease. Most people will have a throat or skin infection, and some may have no symptoms at all. Although healthy people can get invasive GAS disease, people with chronic illnesses like cancer, diabetes, and kidney dialysis, and those who use medications such as steroids have a higher risk.
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What are the early signs and symptoms of necrotizing fasciitis and streptococcal toxic shock syndrome?
Early signs and symptoms of necrotizing fasciitis;
Fever
Severe pain and swelling
Redness at the wound site
Early signs and symptoms of STSS;
Fever
Dizziness
Confusion
A flat red rash over large areas of the body
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How is invasive group A streptococcal disease treated?
GAS infections can be treated with many different antibiotics. Early treatment may reduce the risk of death from invasive group A streptococcal disease. However, even the best medical care does not prevent death in every case. For those with very severe illness, supportive care in an intensive care unit may be needed. For persons with necrotizing fasciitis, surgery often is needed to remove damaged tissue.
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What can be done to help prevent group A streptococcal infections?
The spread of all types of GAS infection can be reduced by good hand washing, especially after coughing and sneezing and before preparing foods or eating. Persons with sore throats should be seen by a doctor who can perform tests to find out whether the illness is strep throat. If the test result shows strep throat, the person should stay home from work, school, or day care until 24 hours after taking an antibiotic. All wounds should be kept clean and watched for possible signs of infection such as redness, swelling, drainage, and pain at the wound site. A person with signs of an infected wound, especially if fever occurs, should seek medical care. It is not necessary for all persons exposed to someone with an invasive group A strep infection (i.e. necrotizing fasciitis or strep toxic shock syndrome) to receive antibiotic therapy to prevent infection. However, in certain circumstances, antibiotic therapy may be appropriate. That decision should be made after consulting with your doctor.
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Date: October 11, 2005 Content source: National Center for Infectious Diseases
Monday, November 28, 2005
Staph Skin Infections in Children
What Is a Staph Infection?
Staph is the shortened form of Staphylococcus (pronounced: staf-uh-low-kah-kus), a type of bacteria. These bacteria can live harmlessly on many skin surfaces, especially around the nose, mouth, genitals, and anus. But when the skin is punctured or broken for any reason, staph bacteria can enter the wound and cause an infection.
There are more than 30 species in the staph family of bacteria; however, most staph infections are caused by the species Staphylococcus aureus (S. aureus). Although the other species of staph bacteria were once believed to be innocent, non-disease-producing inhabitants of skin, it is now known that they can cause illness. For example, other types of staph bacteria can cause urinary tract infections in sexually active adolescents and young women.
S. aureus most commonly causes skin infections like folliculitis, boils, impetigo, and cellulitis that are limited to a small area of a person's skin. But once it enters the bloodstream through a break in the skin, S. aureus can also cause more serious infections in other parts of a person's body, such as the lungs, bones, joints, heart, blood, and central nervous system. These infections are more common in people with certain chronic diseases, in people who are having surgery, and in those with a weakened immune system.
S. aureus can also release toxins (poisons) that may lead to illnesses like food poisoning or toxic shock syndrome.
Who Gets Staph Skin Infections?
Kids, teens, and adults can all develop staph skin infections. People with skin problems like burns or eczema may be more likely to get them, though.Warm, humid environments also contribute to staph infections, and excessive sweating can increase a person's chances of developing the infection. Clusters of cases can occur in groups of people who live in crowded conditions (such as in college dorms), often as a result of poor hygiene and sharing of things like linens and clothing. People who have health problems such as diabetes, malnutrition, cancer, HIV infection, or any other condition that weakens the immune system may be more likely to get more serious staph infections.
What Are the Symptoms of a Staph Skin Infection?
The symptoms a person gets from a staph skin infection depend on the form that the infection takes. Some of the more common staph skin infections are listed below.
Folliculitis (pronounced: fuh-lih-kyoo-lie-tus) is an infection of the hair follicles, the tiny pockets under the skin where hair shafts (strands) grow. In folliculitis, tiny white-headed pimples appear at the base of hair shafts, sometimes with a small red area around each pimple. This occurs often where people shave or have irritated skin from rubbing against clothing.
A furuncle (pronounced: fyoor-un-kul), commonly known as a boil, is a solitary swollen, red, painful lump in the skin, usually due to an infected hair follicle. The lump usually fills with pus, growing larger and more painful until it ruptures and drains. Furuncles are most frequently found on the face, neck, buttocks, armpits, and inner thighs, where small hairs can often be irritated. A cluster of several furuncles is called a carbuncle (pronounced: kar-bun-kul). A person with a carbuncle usually feels ill and feverish.
Impetigo (pronounced: im-puh-tee-go) is a superficial skin infection seen most commonly in young children, but it can sometimes affect adolescents and adults. Most impetigo infections affect a person's face or extremities like the hands and feet. An impetigo lesion begins as a tender, red bump that evolves into a small blister or pimple, and then develops a honey-colored crust. It is a mild condition with no pain or fever, although impetigo blisters may itch and can be spread to other parts of the body by scratching.
Cellulitis (pronounced: sell-yuh-lie-tus) is an infection involving areas of tissue below the skin surface. It begins as a small area of redness, pain, swelling, and warmth on the skin. As this area begins to spread, it can be accompanied by fever and a generally ill feeling. Cellulitis can affect any area of the body, but it's most common on the face or lower legs.
A hordeolum (pronounced: hore-dee-oh-lum), commonly known as a stye, is an infection in the eyelid. It develops when the glands that are connected to the base of the eyelash become obstructed. A person with a stye will usually notice a red, warm, uncomfortable, and sometimes painful swelling near the edge of the eyelid.
Wound infections are generally seen 2 or more days after trauma or surgery. The signs of a wound infection (redness, pain, swelling, and warmth) are similar to those found in cellulitis. A wound infection may be accompanied by fever and a generally ill feeling. Pus or a cloudy fluid can drain from the wound and a yellow crust (like that in impetigo) can develop.
Can I Prevent a Staph Skin Infection?
Staphylococcus aureus bacteria are everywhere. Many healthy people carry staph bacteria in their noses and other parts of the body at various times without getting sick. Our fingers can carry staph bacteria from one area of the body to another, causing infections in wounds or broken skin. Staph bacteria can also spread from person to person, and occasionally through droplets in the air or on contaminated surfaces of objects.
Hand washing is the best way to prevent staph (and other) infections. You can help prevent staph skin infections by bathing or showering daily.
Keep areas of skin that have been injured - such as cuts, scrapes, areas affected by eczema, and rashes caused by allergic reactions or poison ivy - clean and covered, and use any antibiotic ointments or other treatments that your doctor suggests. If someone in your family has a staph infection, don't share towels, sheets, or clothing until the infection has been fully treated.
If you develop a staph infection, be careful not to touch the infected skin. This will prevent the infection from spreading to other skin areas. If you can, keep skin areas affected by staph infections covered to prevent spreading the infection to other parts of the body.
Should I Call My Doctor?
You should call your doctor if you have an area of red, irritated, or painful skin, especially if you see whitish, pus-filled areas or if you have a fever. Also, call your doctor if skin infections seem to be passing from one family member to another or if two or more family members have skin infections at the same time.
How Are Staph Infections Treated?
You can treat most small staph skin infections that aren't serious at home by washing the skin with an antibacterial cleanser, applying an antibiotic ointment, and covering the skin with a clean dressing. To prevent the spread of infection, use a towel only once when you clean an area of infected skin, then wash it in hot water (or use disposable towels).
If an infection becomes severe and turns very red or becomes very sore or is accompanied by fever or a generally ill feeling, you should call your doctor. For severe infections, your doctor may prescribe an antibiotic for you. If so, be sure to take your antibiotic as prescribed for as many days as your doctor directs. If a person has a large, pus-filled staph infection, it may need to be drained by a doctor.
What Can I Do to Feel Better?
The time a staph skin infection take to heal varies depending on the type of infection and whether a person gets treatment for it. A boil, for example, may take 10 to 20 days to heal without treatment, but treatment will speed this process up. Most styes, on the other hand, go away on their own within several days.
To help relieve pain from a skin infection, try soaking the skin in warm water or applying hot, moist washcloths to the area. You can also apply a heating pad or a hot water bottle to the skin for about 20 minutes, three or four times a day. Pain relievers like acetaminophen (such as Tylenol) or ibuprofen (such as Advil or Motrin) can help reduce pain until the infection subsides
Styes can be treated using warm compresses over the eye (with the eye closed) three or four times a day. Occasionally, a stye will require a topical antibiotic. See your doctor if a stye doesn't go away in a few days.
If you get a staph infection on skin areas that you normally shave, avoid shaving, if possible, until the infection clears up. If you do have to shave the area, use a clean disposable razor or clean your electric razor after each use.
Updated and reviewed by: Elana Pearl Ben-Joseph, MDDate reviewed: October 2003Originally reviewed by Stephen Eppes, MD
KidsHealth
Staph Infections
Definition
Staphylococcal (staph) infections are communicable conditions caused by certain bacteria and generally characterized by the formation of abscesses. They are the leading cause of primary infections originating in hospitals (nosocomial infections) in the United States.
Description
Classified since the early twentienth century as among the deadliest of all disease-causing organisms, staph exists on the skin or inside the nostrils of 20-30% of healthy people. It is sometimes found in breast tissue, the mouth, and the genital, urinary, and upper respiratory tracts.
Although staph bacteria are usually harmless, when injury or a break in the skin enables the organisms to invade the body and overcome the body's natural defenses, consequences can range from minor discomfort to death. Infection is most apt to occur in:
newborns
women who are breastfeeding
individuals whose immune systems have been undermined by radiation treatments, chemotherapy, or medication
intravenous drug users
those with surgical incisions, skin disorders, and serious illness like cancer, diabetes, and lung disease
Types of infections
Staph infections produce pus-filled pockets (abscesses) located just beneath the surface of the skin or deep within the body. Risk of infection is greatest among the very young and the very old.
A localized staph infection is confined to a ring of dead and dying white blood cells and bacteria. The skin above it feels warm to the touch. Most of these abscesses eventually burst, and pus that leaks onto the skin can cause new infections.
A small fraction of localized staph infections enter the bloodstream and spread through the body. In children, these systemic (affecting the whole body) or disseminated infections frequently affect the ends of the long bones of the arms or legs, causing a bone infection called osteomyelitis. When adults develop invasive staph infections, bacteria are most apt to cause abscesses of the brain, heart, kidneys, liver, lungs, or spleen.
Staphylococcus aureus
Named for the golden color of the bacteria grown under laboratory conditions, S. aureus is a hardy organism that can survive in extreme temperatures or other inhospitable circumstances. About 70-90% of the population carry this strain of staph in the nostrils at some time. Although present on the skin of only 5-20% of healthy people, as many as 40% carry it elsewhere, such as in the throat, vagina, or rectum, for varying periods of time, from hours to years, without developing symptoms or becoming ill.
S. aureus flourishes in hospitals, where it infects healthcare personnel and patients who have had surgery; who have acute dermatitis, insulin-dependent diabetes, or dialysis-dependent kidney disease; or who receive frequent allergy-desensitization injections. Staph bacteria can also contaminate bedclothes, catheters, and other objects.
S. aureus causes a variety of infections. Boils and inflammation of the skin surrounding a hair shaft (folliculitis) are the most common. Toxic shock (TSS) and scalded skin syndrome (SSSS) are among the most serious.
TOXIC SHOCK
Toxic shock syndrome is a life-threatening infection characterized by severe headache, sore throat, fever as high as 105°F, and a sunburn-like rash that spreads from the face to the rest of the body. Symptoms appear suddenly; they also include dehydration and watery diarrhea.
Inadequate blood flow to peripheral parts of the body (shock) and loss of consciousness occur within the first 48 hours. Between the third and seventh day of illness, skin peels from the palms of the hands, soles of the feet, and other parts of the body. Kidney, liver, and muscle damage often occur.
SCALDED SKIN SYNDROME
Rare in adults and most common in newborns and other children under the age of five, scalded skin syndrome originates with a localized skin infection. A mild fever and/or an increase in the number of infection-fighting white blood cells may occur.
A bright red rash spreads from the face to other parts of the body and eventually forms scales. Large, soft blisters develop at the site of infection and elsewhere. When they burst, they expose inflamed skin that looks as if it had been burned.
MISCELLANEOUS INFECTIONS
S. aureus can also cause:
arthritis
bacteria in the bloodstream (bacteremia)
pockets of infection and pus under the skin (carbuncles)
tissue inflammation that spreads below the skin, causing pain and swelling (cellulitis)
inflammation of the valves and walls of the heart (endocarditis)
inflammation of tissue that enclosed and protects the spinal cord and brain (meningitis)
inflammation of bone and bone marrow (osteomyelitis)
pneumonia
Other strains of staph
S. EPIDERMIDIS.
Capable of clinging to tubing (as in that used for intravenous feeding, etc.), prosthetic devices, and other non-living surfaces, S. epidermidis is the organism that most often contaminates devices that provide direct access to the bloodstream.
The primary cause of bacteremia in hospital patients, this strain of staph is most likely to infect cancer patients, whose immune systems have been compromised, and high-risk newborns receiving intravenous supplements.
S. epidermidis also accounts for two of every five cases of prosthetic valve endocarditis. Prosthetic valve endocarditis is endocarditis as a complication of the implantation of an artificial valve in the heart. Although contamination usually occurs during surgery, symptoms of infection may not become evident until a year after the operation. More than half of the patients who develop prosthetic valve endocarditis die.
STAPHYLOCOCCUS SAPROPHYTICUS
Existing within and around the tube-like structure that carries urine from the bladder (urethra) of about 5% of healthy males and females, S. saprophyticus is the second most common cause of unobstructed urinary tract infections (UTIs) in sexually active young women. This strain of staph is responsible for 10-20% of infections affecting healthy outpatients.
Causes and symptoms
Staph bacteria can spread through the air, but infection is almost always the result of direct contact with open sores or body fluids contaminated by these organisms.
Staph bacteria often enter the body through inflamed hair follicles or oil glands. Or they penetrate skin damaged by burns, cuts and scrapes, infection, insect bites, or wounds.
Multiplying beneath the skin, bacteria infect and destroy tissue in the area where they entered the body. Staph infection of the blood (staphylococcal bacteremia) develops when bacteria from a local infection infiltrate the lymph glands and bloodstream. These infections, which can usually be traced to contaminated catheters or intravenous devices, usually cause persistent high fever. They may cause shock. They also can cause death within a short time.
Warning signs
Common symptoms of staph infection include:
pain or swelling around a cut, or an area of skin that has been scraped
boils or other skin abscesses
blistering, peeling, or scaling of the skin; this is most common in infants and young children
enlarged lymph nodes in the neck, armpits, or groin
A family physician should be notified whenever:
Lymph nodes in the neck, armpits, or groin become swollen or tender.
An area of skin that has been cut or scraped becomes painful or swollen, feels hot, or produces pus. These symptoms may mean the infection has spread to the bloodstream.
A boil or carbuncle appears on any part of the face or spine. Staph infections affecting these areas can spread to the brain or spinal cord.
A boil becomes very sore. Usually a sign that infection has spread, this condition may be accompanied by fever, chills, and red streaks radiating from the site of the original infection.
Boils that develop repeatedly. This type of recurrent infection could be a symptom of diabetes.
Diagnosis
Blood tests that show unusually high concentrations of white blood cells can suggest staph infection, but diagnosis is based on laboratory analysis of material removed from pus-filled sores, and on analysis of normally uninfected body fluids, such as, blood and urine. Also, x rays can enable doctors to locate internal abscesses and estimate the severity of infection. Needle biopsy (removing tissue with a needle, then examining it under a microscope) may be used to assess bone involvement.
Treatment
Superficial staph infections can generally be cured by keeping the area clean, using soaps that leave a germ-killing film on the skin, and applying warm, moist compresses to the affected area for 20-30 minutes three or four times a day.
Severe or recurrent infections may require a seven to 10 day course of treatment with penicillin or other oral antibiotics. The location of the infection and the identity of the causal bacteria determines which of several effective medications should be prescribed.
In case of a more serious infection, antibiotics may be administered intravenously for as long as six weeks. Intravenous antibiotics are also used to treat staph infections around the eyes or on other parts of the face.
Surgery may be required to drain or remove abscesses that form on internal organs, or on shunts or other devices implanted inside the body.
Alternative treatment
Alternative therapies for staph infection are meant to strengthen the immune system and prevent recurrences. Among the therapies believed to be helpful for the person with a staph infection are yoga (to stimulate the immune system and promote relaxation), acupuncture (to draw heat away from the infection), and herbal remedies.
Herbs that may help the body overcome, or withstand, staph infection include:
Garlic (Allium sativum). This herb is believed to have anitbacterial properties. Herbalists recommend consuming three garlic cloves or three garlic oil capsules a day, starting when symptoms of infection first appear.
Cleavers (Galium aparine). This anti-inflammatory herb is believed to support the lymphatic system. It may be taken internally to help heal staph abscesses and reduce swelling of the lymph nodes. A cleavers compress can also be applied directly to a skin infection.
Goldenseal (Hydrastis canadensis). Another herb believed to fight infection and reduce imflammation, goldenseal may be taken internally when symptoms of infection first appear. Skin infections can be treated by making a paste of water and powdered goldenseal root and applying it directly to the affected area. The preparation should be covered with a clean bandage and left in place overnight.
Echinacea (Echinacea spp.). Taken internally, this herb is believed to have antibiotic properties and is also thought to strengthen the immune system.
Thyme (Thymus vulgaris), lavender (Lavandula officinalis), or bergamot (Citrus bergamot) oils. These oils are believed to have antibacterial properties and may help to prevent the scarring that may result from skin infections. A few drops of these oils are added to water and then a compress soaked in the water is applied to the affected area.
Tea tree oil (Melaleuca spp.). Another infection-fighting herb, this oil can be applied directly to a boil or other skin infection.
Prognosis
Most healthy people who develop staph infections recover fully within a short time. Others develop repeated infections. Some become seriously ill, requiring long-term therapy or emergency care. A small percentage die.
Prevention
Healthcare providers and patients should always wash their hands thoroughly with warm water and soap after treating a staph infection or touching an open wound or the pus it produces. Pus that oozes onto the skin from the site of an infection should be removed immediately. This affected area should then be cleansed with antiseptic or with antibacterial soap.
To prevent infection from spreading from one part of the body to another, it is important to shower rather than bathe during the healing process. Because staph infection is easily transmitted from one member of a household to others, towels, washcloths, and bed linens used by someone with a staph infection should not be used by anyone else. They should be changed daily until symptoms disappear, and laundered separately in hot water with bleach.
Children should frequently be reminded not to share:
brushes, combs, or hair accessories
caps
clothing
sleeping bags
sports equipment
other personal items
A diet rich in green, yellow, and orange vegetables can bolster natural immunity. A doctor or nutritionist may recommend vitamins or mineral supplements to compensate for specific dietary deficiencies. Drinking eight to 10 glasses of water a day can help flush disease-causing organisms from the body.
Because some strains of staph bacteria are known to contaminate artificial limbs, prosthetic devices implanted within the body, and tubes used to administer medication or drain fluids from the body, catheters and other devices should be removed on a regular basis, if possible, and examined for microscopic signs of staph. Symptoms may not become evident until many months after contamination has occurred, so this practice should be followed even with patients who show no sign of infection.
Abscess
A cavity containing pus surrounded by inflamed tissue.
Endocarditis
Inflammation of the lining of the heart, and/or the heart valves, caused by infection.
Nosocomial infections
Infections that were not present before the patient came to a hospital, but were acquired by a patient while in the hospital.
For Your Information
Books
Bennett, J. Claude, and Fred Plum, eds. Cecil Textbook of Medicine. Philadelphia: W. B. Saunders Co., 1996.
Civetta, Joseph M., et al., eds. Critical Care. Philadelphia: Lippincott-Raven Publishers, 1997.
Harrison's Principles of Internal Medicine. Ed. Anthony S. Fauci, et al. New York: McGraw-Hill, 1997.
The Editors of Time-Life Books. The Medical Advisor: The Complete Guide to Alternative and Conventional Treatments. Alexandria, VA: Time Life, Inc., 1996.
Source: Gale Encyclopedia of Medicine, Published December, 2002 by the Gale Group
The Essay Author is Maureen Haggerty.
Health AtoZ
Bacteria - by rachel Age 13
Strep throat, cholera, pneumonia, whooping cough. These diseases, and more, are often the only things bacteria get credit for doing. I have researched these microscopic, unicellular organisms and found out that bacteria are responsible for much more than just diseases. There are thousands of kinds of bacteria. Most of them are harmless to humans. There are about two thousand species of bacteria identified, and even more where that came from. It is possible for bacteria to reproduce as often as every twenty minutes. If all the newly formed bacteria survived, there would be about 500,000 new bacteria cells every six hours. That is a lot! Thankfully, this does not happen. Bacteria are the oldest, the simplest, and the most numerous forms of life. Bacteria were here 3.5 billion years ago. A bacterium's structure is quite simple. From the outside in, there is the capsule, the cell wall, and then the cell membrane. Inside is the cytoplasm, which holds the hereditary material, and at times the endospore. There are no intracellular organelles.
Even though there are 2.5 billion bacteria in one gram of soil, you may never see a single bacteria in your entire life. If you lined 10,000 bacteria up, side by side, it would only make up 2.5 centimeters of space and could only be seen under a powerful microscope. Even though bacteria are extremely small, they are found nearly everywhere.
Bacteria are even found in the Dead Sea. For instance, the bacteria that causes acne can be found on a pay phone. There are seven different kinds of bacteria on a locker room shower floor. On a movie theater seat and a school lunch table there are five different kinds of bacteria
Even though bacteria are so tiny, they play a very large role in their ecosystem. Every living thing would not be here today if it were not for bacteria. Decomposing is one of the most important jobs bacteria do. This is also called mineralization. When an organism dies in the wild, it just sits and rots. What is happening is that bacteria are releasing carbon to the atmosphere which plants use. With no carbon dioxide there would be no photosynthesis, which narrows down to Eno food. Instead of this catastrophe, bacteria do us a huge favor. By decomposing the dead organisms, the bacteria release essential nutrients into the air and soil. The simpler material made by decomposition can be used by both autotrophic and heterotrophic organisms. Autotrophs use it to help them make food and heterotrophs use it as food. As you can tell, the bacteria that decompose are very important to the earth's ecology. If these bacteria disappeared, everything would suffer greatly. The cycle goes like this: The grass is eaten by a rabbit. Then the rabbit is eaten by the hawk, then the hawk dies. After the hawk dies, bacteria decompose it and returns it to the grass that the rabbit eats, and it all starts once again.
Another very important job of bacteria is something called nitrogen fixing, or nitrogen cycling. Have you ever wondered why farmers may replant their fields with alfalfa, soybean, or clover in a crop rotation? Well, certain kinds of bacteria called rhizobium live in nodules on the roots of these plants in symbiosis. Rhizobium do the nitrogen cycling. Green plants cannot use the nitrogen in the air, or atmospheric nitrogen. Nitrogen-fixing bacteria (as part of their metabolism) change atmospheric nitrogen into simpler substances call nitrites. Nitrites are needed by green plants. Think about this: In order to make protein, a cow needs nitrogen. This comes from eating grass, which gets its nitrogen from bacteria. Then we eat the cow. So this little chain affects a lot of living things. If there were no nitrogen-fixing bacteria, there would be no plants because the nitrogen in the soil would be used up too quickly. Nitrogen-fixing bacteria helps to replace the nitrogen in the soil so that green plants can survive and flourish. Aren't you starting to feel very grateful to bacteria now? They do a lot of work for us every day. And there is still more.
Vast numbers of bacteria live in our bodies. One example is found in the intestine. This bacteria and humans have formed a symbioses with each other. The bacteria help us with digestion and to produce vitamins. In exchange, they soak up a little extra food for themselves. Neat. Huh? Most dairy products are made by or with the help of bacteria. Some dairy foods are cheese, buttermilk, yogurt, and sour cream. Some other kinds of foods that involve bacteria in their production are pickles and high fructose corn syrup. Can you imagine our soda without high fructose corn syrup, or any other sweet foods for that matter? A hamburger with no cheese or pickles, or chili with no sour cream? The possibilities are endless.
Bacteria help in the production of fuel in two major ways. Some bacteria decompose compost, garbage and sewage and help make methane. Methane is a valuable natural gas. It is used widely as a fuel. Also, over time, the earth's pressure has changed dead and decomposed animals and plants into coal, which is also a widespread fuel.
Bacteria is very important in medicine. Bacteria can actually help to fight themselves. Doctors and scientists have figured out how to use dead or weakened bacteria to prevent other bacterial diseases. This process is called vaccination. Vaccination has helped us all become a lot healthier then we were a hundred years ago. Bacteria also make, or help to make, drugs, hormones, or antibodies.
Bacteria, scientists are discovering, can even help to break down oil to make clean-up after an oil spill easier. This is a big plus for the environment. Scientists are even looking for a use for bacterial-made plastics. In the future, this could be handy and could be broken down easier in the garbage dumps. A group called cyanobacteria produces oxygen. Cyanobacteria is also a source of food. Pink flamingos are one species that feed on cyanobacteria. Lastly, bacteria play a large part in many commercial industries. They help in tanning, making linen, curing tea and tobacco leaves, extracting precious metals from rock, coloring foods, coloring cosmetics, tenderizing meat, removing stains, processing paper, processing cloth, changing one chemical into another, and more!
Bacteria are an extremely important part of your ecosystem. If, for some reason, bacteria could not do their job, or suddenly and inexplicably disappeared, imagine what a mess we would be in. From what I have learned about bacteria, the earth would probably still be the barren wasteland it was 4.6 billion years ago if bacteria had never showed up. Bacteria started everything, and could very well end everything just as quickly. Bacteria do so much for us, where would we be without them?
American Musem of Natural History
bibliography:
Aborn, Shana. "How Clean Is It?" Ladies Home Journal 114 (February 1997): 112-115.
Arms, Karen and Pamela S. Camp. Biology. Philadelphia: Saunders College Publishing, 1982.
"Bacteria: Life History and Ecology" www.ucmp.berkely.edu/bacteria/bacteria.htmI 1/16/98
Brian, Dr. Tony and David Parker. "What Are Bacteria?" World Book's Young Scientist, 5, (1991) 128.
Crockett, Lawrence J. "Bacteria" Academic American Encyclopedia 3, (1994): 14Ð18.
Flannery, Maura C. "Back to Bacteria" The American Biology Teacher 59 (June 1997): 370Ð37.
Maggs, Dr. A. "Bacteria-The Basic Facts," www-micro.msb.le.ac.uk/MBChB/3a.html
Maton, Anthea and Jean Hopkins. Exploring Life Science. Upper Saddle River: Prentice Hall Inc., 1997.
Neft, Naomi "Bacteria" Merit Student's Encyclopedia 2, (1990): 501 Rakosy, A.W. "Bacteria" Children's Britanica 2, (1994): 320.
Raven, Peter H. and George B. Johnson. Understanding Biology. St. Louis: Times Mirror/Mosby College Publishing, 1988.
Regents Biology. "Monerans, Protists, and Viruses" www.ulster.net/(mycoman/rbactnot.html, 1/15/98.
Schlessinger, David. "Bacteria" The World Book 2, (1990): 770.
Still, William B. "Bacteria" Encyclopedia of the Sciences 1, (1963): 75-77.
Ycas, Martynas "Bacteria" Collier's Encyclopedia 3, (1993): 444-448.
Sunday, November 27, 2005
Classification of Bacteria
Classification (taxonomy) of Bacteria :
Earlier in the course we talked about the various taxonomic categories:
Kingdom
Phylum (called Divisions in plant biology)
Class
Order (called Sections in bacterial taxonomy)
Family
Genus
Species
These are listed in decending order from most inclusive [Kingdom] to least inclusive [Species].
Bacteria are currently divided into 4 Divisions (phyla) which are in turn divided into 7 Classes based on differences in cell wall characteristics. The classes are divided into a total of 33 Sections (rather than orders). The bacteria belong to the Kingdom Monera (Kingdom Procaryotae) , which currently includes the:
true bacteria ( Eubacteria ) - includes all of the bacteria of medical significance
blue-green algae ( Cyanobacteria ) - photosynthetic algae-like organisms (not true algae)
archaea ( Archeobacteria ) - primitive inhabitants of extreme environments
The bacteria of medical significance (those that cause human disease) are included in these groups:
Gram negative rods ( Enterobacteria and others)
Obligate intracellular parasites ( Ricckettsia and Chlamydia)
Gram negative curved rods ( vibrios, Helicobacter, Campylobacter, and others)
Gram negative cocci ( Neisseria and others )
Gram positive rods ( Bacillus, Clostridium, and others )
Gram positive cocci ( Staphylococcus, Streptococcus, and others )
Acid fast rods ( Mycobacterium, Nocardia )
Spirochetes ( Treponema, Borellia, and others )
Mycoplasmas (tiny bacteria that lack a cell wall)
In the above list, the italicized words are genera (plural of genus). Genus and species names are always italicized (or underlined) to indicate that they are scientific names. The genus name is always capitalized, and the species name is never capitalized.
In biology, species may be further subdivided into sub-species. Bacterial sub-species are called strains and are designated by names, numbers, letters, or combinations of letters and numbers (eg. Escherichia coli strain 0157-H7 is the strain that has recently caused a number of human deaths). Strains are simply subgroups that have characteristics that differ in some important way from other subgroups of the same species. In some groups (eg. the genus Salmonella ), the term serovar is used to designate a serologically distinct strain. We'll talk more about serology when we talk about antigen-antibody reactions.
Some of the characteristics of bacteria that are employed in their classification and identification are:
morphology - cell shape and size
staining reactions - especially gram staining reaction
metabolism - biochemical reactions
growth characteristics including colony size, shape, and color
environmental requirements - eg. oxygen tolerance, temperature tolerance, etc.
serologic reactions - antigen-antibody reactions
phage typing - using bacteriophages to identify bacterial strains
DNA hybridization - to determine closeness of relationship between various bacteria
base sequence of nucleic acids
protein types - determined by polyacrylamide gel electrophoresis [ PAGE ]
lipid types
other characteristics
Classical determinative bacteriology is largely based upon the first five types of characteristics listed above. Bacteria are identified to species by determining their cell size, shape, staining characteristics, environmental requirements and metabolic characteristics. The substrates that a bacterium can utilize as energy sources, and the by-products that are produced when it utilizes those substrates are the basis for the metabolic characterization of bacteria.
The "bible" of bacterial identification is a book called Bergey's Manual of Determinative Bacteriology. Bergey is long dead, but the American Society for Microbiology continues to revise and publish the book. It is currently in its ninth edition.
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Clinical bacteria are grouped into five categories based on gram stain appearance under the light microscope. Two groups have a general rounded shape and stain either red or blue, the cocci. Two groups have a general rod-like shape and stain either red or blue, the bacilli. By far the largest group numerically is the gram negative bacilli group. Gram negative organisms have thinner cell walls and the cell wall composition is different from that of gram positive organisms. This difference accounts for general differences in how both virulence factors and antigentic determinants are expressed. This difference also accounts for some general distinctions in susceptibility to antibiotic drugs. Thus the gram stain is considered by many as the single most important characteristic of clinical bacteria. However the gram stain itself is not used for the identification of organisms. One rare exception would of course be a gram stain of GNID in urethral discharge.
Bacterial Classifications and Terms
Descriptive terms are used to broadly categorize clinical bacteria in several useful ways.
They are categorized according to their gram stain characteristics as described above.
They are classified taxonomically as to genera and species. An inclusive alphabetical list would be useful to indicate the scope of the numbers of kinds of organisms encompassed within the field of clinical bacteriology. The names of the clinical bacteria in such a list often describe distinctive characteristics, as for example Mycobacterium, which has mycolic acids within the cell wall. The names have sometimes been problematic. Since 1974 there has been a proliferation of new names. Names of some genera of clinical bacteria have changed more than once. Some genera have two names until concensus is reached. Sometimes taxa* are defined predominantly based on DNA homology, sometimes not. But, now with reliably routine methods of genome sequencing, the taxonomic similarities and dissimilarities which distinguish clinical bacteria can also be based on DNA code; classifications may become more clear and less subject to change.*sing. taxon, pl. taxa
Clinical bacteria are categorized based on whether they require strict anaerobic conditions for growth. If they do, they are called anaerobes, as for example Fusobacterium sp. If they do not, the term facultative is generally used. Facultative means that they are flexible and can grow in both conditions, as for example E coli. Very few organisms strictly require aerobic conditions for growth. So in most cases an organism is said to be either an anaerobe or a facultative organism. Anaerobes account for 5-10% of all clinical infections
Clinical bacteria are categorized according to which region of the body they inhabit as part of normal flora or from which part they are frequently isolated or cause disease, as for example the family Enterobacteriaceae, which includes many familiar gram negative enteric bacilli.. Sources such as the cerebrospinal fluid and blood should never harbor any bacterial organisms and therefore any and all organisms from these sources are considered dangerous and are indications for antimicrobial therapy.
Clinical bacteria are classified according to how dangerous they are. Pathogens are always likely to cause disease. Organisms which cause disease only when they have a special opportunity to gain entrance inside the body are called opportunistic, as for example Bacteroides fragilis, or Clostridium difficile. Some organisms such as the Streptococcus viridans group can gain entry into the bloodstream and quietly become entrenched on the mitral valves of the heart causing a problem only after a long period as a cumulative effect. Some pathogens proactively create portals of entry. These organisms are called invasive, as for example, Salmonella enteritidis, or strains of Streptococcus pyogenes, the sensationalised, "flesh eating," bacteria.
Perhaps a useful system of categorization would give an indication of the probability of infection by a particular organism. True, the CDC publishes a weekly report entitled MMWR and also publishes yearly figures on the incidence of infection of the various disease causing agents including bacteria which are thorough and authoritative. And it would be irresponsible for health care professionals to ignore a given bacterial agent simply because its incidence were very low. If for example a particular organism is only seen in the tropics, it may be of interest to someone considering visiting a tropical venue or to someone who has visited such a venue or to a health care professional serving the needs of such persons. But to Mary and John Q. Public for whom the names of the clinical bacteria are just a list of strange latin binomials, the important questions are, "Which are relevant, how are they significant, and what would be the probability that they would personally affect Mary and John?" So for proper perspective of relative incidence and probability, we have included various anecdotes which even health professionals may find humorous. If a given impression is grossly misleading, let us know. Upon completion, there will have been two or three intentional misstatements just to see whether you are awake or asleep at the wheel.
Classification of BacteriaBacteria - Life History and Ecology
Bacteria grow in a wide variety of habitats and conditions.
When most people think of bacteria, they think of disease-causing organisms, like the Streptococcus bacteria growing in culture in this picture, which were isolated from a man with strep throat. While pathogenic bacteria are notorious for such diseases as cholera, tuberculosis, and gonorrhea, such disease-causing species are a comparatively tiny fraction of the bacteria as a whole.
Bacteria are so widespread that it is possible only to make the most general statements about their life history and ecology. They may be found on the tops of mountains, the bottom of the deepest oceans, in the guts of animals, and even in the frozen rocks and ice of Antarctica. One feature that has enabled them to spread so far, and last so long is their ability to go dormant for an extended period.
Bacteria have a wide range of envronmental and nutritive requirements.
Most bacteria may be placed into one of three groups based on their response to gaseous oxygen. Aerobic bacteria thrive in the presence of oxygen and require it for their continued growth and existence. Other bacteria are anaerobic, and cannot tolerate gaseous oxygen, such as those bacteria which live in deep underwater sediments, or those which cause bacterial food poisoning. The third group are the facultative anaerobes, which prefer growing in the presence of oxygen, but can continue to grow without it.
Bacteria may also be classified both by the mode by which they obtain their energy. Classified by the source of their energy, bacteria fall into two categories: heterotrophs and autotrophs. Heterotrophs derive energy from breaking down complex organic compounds that they must take in from the environment -- this includes saprobic bacteria found in decaying material, as well as those that rely on fermentation or respiration.
The other group, the autotrophs, fix carbon dioxide to make their own food source; this may be fueled by light energy (photoautotrophic), or by oxidation of nitrogen, sulfur, or other elements (chemoautotrophic). While chemoautotrophs are uncommon, photoautotrophs are common and quite diverse. They include the cyanobacteria, green sulfur bacteria, purple sulfur bacteria, and purple nonsulfur bacteria. The sulfur bacteria are particularly interesting, since they use hydrogen sulfide as hydrogen donor, instead of water like most other photosynthetic organisms, including cyanobacteria.
Bacteria play important roles in the global ecosystem.
The ecosystem, both on land and in the water, depends heavily upon the activity of bacteria.
The cycling of nutrients such as carbon, nitrogen, and sulfur is completed by their ceaseless labor.
Organic carbon, in the form of dead and rotting organisms, would quickly deplete the carbon dioxide in the atmosphere if not for the activity of decomposers. This may not sound too bad to you, but realize that without carbon dioxide, there would be no photosynthesis in plants, and no food. When organisms die, the carbon contained in their tissues becomes unavailble for most other living things. Decomposition is the breakdown of these organisms, and the release of nutrients back into the environment, and is one of the most important roles of the bacteria.
The cycling of nitrogen is another important activity of bacteria. Plants rely on nitrogen from the soil for their health and growth, and cannot acquire it from the gaseous nitrogen in the atmosphere. The primary way in which nitrogen becomes available to them is through nitrogen fixation by bacteria such as Rhizobium, and by cyanobacteria such as Anabaena, Nostoc, and Spirulina, shown at right. These bacteria convert gaseous nitrogen into nitrates or nitrites as part of their metabolism, and the resulting products are released into the environment. Some plants, such as liverworts, cycads, and legumes have taken special advantage of this process by modifying their structure to house the basteria in their own tissues. Other denitrifying bacteria metabolize in the reverse direction, turning nitrates into nitrogen gas or nitrous oxide. When colonies of these bacteria occur on croplands, they may deplete the soil nutrients, and make it difficult for crops to grow.
What are Bacteria?
Bacteria
Borrelia burgdorferiNelson, ASM MicrobeLibrary
Bacteria consist of only a single cell, but don't let their small size and seeming simplicity fool you. They're an amazingly complex and fascinating group of creatures. Bacteria have been found that can live in temperatures above the boiling point and in cold that would freeze your blood. They "eat" everything from sugar and starch to sunlight, sulfur and iron. There's even a species of bacteria—Deinococcus radiodurans—that can withstand blasts of radiation 1,000 times greater than would kill a human being.
Classification
Leucothrix mucor Appl. Environ. Microbiol. 55:1435-1446, 1989
Bacteria fall into a category of life called the Prokaryotes (pro-carry-oats). Prokaryotes' genetic material, or DNA, is not enclosed in a cellular compartment called the nucleus.
Bacteria and archaea are the only prokaryotes. All other life forms are Eukaryotes (you-carry-oats), creatures whose cells have nuclei.
(Note: viruses are not considered true cells, so they don't fit into either of these categories.)
Early Origins
Bacteria are among the earliest forms of life that appeared on Earth billions of years ago. Scientists think that they helped shape and change the young planet's environment, eventually creating atmospheric oxygen that enabled other, more complex life forms to develop. Many believe that more complex cells developed as once free-living bacteria took up residence in other cells, eventually becoming the organelles in modern complex cells. The mitochondria (mite-oh-con-dree-uh) that make energy for your body cells is one example of such an organelle.
What They Look Like
Ball-shaped StreptococciSimonson, ASM MicrobeLibrary
There are thousands of species of bacteria, but all of them are basically one of three different shapes. Some are rod- or stick-shaped and called bacilli (buh-sill-eye).
Others are shaped like little balls and called cocci (cox-eye).
Others still are helical or spiral in shape, like the Borrelia pictured at the top of this page.
Some bacterial cells exist as individuals while others cluster together to form pairs, chains, squares or other groupings.
Where They're Found
Bacteria live on or in just about every material and environment on Earth from soil to water to air, and from your house to arctic ice to volcanic vents. Each square centimeter of your skin averages about 100,000 bacteria. A single teaspoon of topsoil contains more than a billion (1,000,000,000) bacteria.
How They Move
Some bacteria move about their environment by means of long, whip-like structures called flagella. They rotate their flagella like tiny outboard motors to propel themselves through liquid environments. They may also reverse the direction in which their flagella rotate so that they tumble about in one place.
Other bacteria secrete a slime layer and ooze over surfaces like slugs. Others are fairly stationary.What They EatSome bacteria are photosynthetic (foe-toe-sin-theh-tick)—they can make their own food from sunlight, just like plants. Also like plants, they give off oxygen. Other bacteria absorb food from the material they live on or in. Some of these bacteria can live off unusual "foods" such as iron or sulfur. The microbes that live in your gut absorb nutrients from the digested food you've eaten.
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Bacteria are very small, single-cell organisms which occur as little round balls, tiny short sticks, or spirals that look like springs. These three basic forms are often stuck together in long strings, or clusters that look like little squares, cubes, or random grape-like clusters.
Size of Bacteria
An individual bacterium is very tiny. They are usually one or two micrometers across. Since micro means 1/000,000 (one-millionth), they are commonly one millionth of a meter in diameter. A meter is 39.37 inches (3.33 inches longer than a yard). How many bacteria lying snugly side-by-side would it take to reach one meter? Since they are one to two micrometers wide, it would take about one million lying side by side to reach one meter, or 500,000 if they were 2 micrometers wide.
Shapes of Bacteria
While some bacteria are small spheres, others are shaped like tiny hotdogs (frankfurters, or sausages). Some species of bacteria hang together in chains like a chain of sausages. Often these chains contain only a few cells, but some form chains of hundreds of cells. The hotdog shaped bacteria are usually 2 or 3 times as long as wide, but some are very long in comparison to width. Some individual cells are long shaped like a needle.
Many species of bacteria reproduce by a wall forming across the cell dividing the orginal cell into two daughter cells having the same shape and genetic composition. Since the cells are growing, by the time division (fission) is completed each of the daughters may be as large as the mother cell was before it began fission (splitting).
Arrangement of Bacteria
Some bacteria can divide every 12 to 20 minutes. Often they hang to together by the outer membranes (skin of the sausage) for a while. Suppose that the bacteria in a culture are dividing every 20 minutes on average. Suppose they then hang together for 10 minutes before becoming separated. If you draw time-diagram, you can see that about half the cells will be singles and half doubles (diploid).
Some daughter cells hang together for a long time and form long flexible chains. In some species, the the cross walls do not pinch of off for a long time and long rigid filaments form. In fact, some genera of bacteria are notable for forming long chains which which to not break apart until the culture runs out of food and is dying.
While round bacteria also form chains, some species form squares or cubes. Imagine a single round bacterium which divides and the two cells hang together. Then each of the daughter cells divides in the same plane. You now have a short chain of 4 cells. Alternatively, Suppose the second set of cell fissions occur at right angle to the first, you would now have four cells in a sqare packet. Suppose each cell then divides in the 3rd plane, you now have a cube-shaped packet of 8 cells. After 3 more divisions you have a large packet of 64 cells, but with the microscope you can usually see they are really 4 cubes of 16 cells each.
This was very long story about fission of bacteria. But you can see that the shape and arrangement of bacteria can give you some idea of the genus of an unknown bacterium by looking at the shape and arrangement of cells in a growing culture. However, toy microscopes do not have the resolution to see bacteria and I do not recommend a beginning student buy such cheap instruments. You will be disappointed. It is better to find a doctor, teacher, or lab technician who will take some time to let you look thru his microscope at some bacteria. However, it is difficult to find cultures in the optimum condition to show cubic packets, chains, etc. on the same day because your mentor in not likely to be working with so many different kinds of bacteria on the day you visit.
How Bacteria Eat
Bacteria do not have a mouth. They make proteins called enzymes inside the cell and these travel thru the cell wall into the surrounding medium. The enzymes chop the food into tiny subunits which then come into the bacteria cell by osmosis or active transport. Active transport is the process by which the cell grabs a molecule of glucose or other food and pulls it in thru the cell wall. Many specialized proteins and other molecules made by the bacterium are involved in this active transport process. Perhaps someday you can figure out ways to study the mechanisms of active transport.
The process by which the enzyme chops the food into subunits is also very complex and specific and usually requires one molecule of water for each split. If water is consumed, the chopping process is called hydrolysis (splitting by water).
The enzyme which is able to hydrolyse lactose (milk sugar) will not fit into a protein molecule the right way to be able to hydrolyze protein. Further, lactase (an enzyme able to hydrolyse lactose) will not be able to fit into a starch molecule to split it. Thus, if a bacterium is going to eat many kinds of foods, it must have many kinds of hydrolases because enzymes do very specific jobs.
Some bacteria have many kinds of enzymes and can eat many kinds of foods. Other bacteria have few enzymes and are able to digest very few kinds of food. Bacteria which do not have the correct enzymes can still live off a given food by growing where other bacteria have ready broken the food down. This is similar to a gull eating bits of sealion meat left by a shark that killed the sealion. Thus, in food processing we might used a "mixed culture" and get an especially delightfully tasting and digestible food. This website has some very interesting experiments like this for the home fermentation of special foods.
We have just learned that bacteria differ in the foods they are able to digest and that is one of the ways we can tell them apart. For example some species of Clostridium are able to digest carbohydrates and make alcohols and very smelly organic acids but can't digest proteins. Other Clostridium species can digest proteins and cause serious problems in human wounds, but do not digest carbohydrates. A few Clostridium species can digest proteins and carbohydrates. Thus, trying to grow an unknown Clostrium species upon separate carbohydrate and protein media can help us identify the unknown species.
Why would anyone want to know the name of a Clostridium? Simple, some Clostridium species are harmless and some are human pathogens (causing disease in humans). Suppose a doctor found a Clostridium in a deep wound in your body, you would suddenly be very interested wouldn't you. Or suppose you want a career helping other people; you might want to learn such thing so you could be a bacteriologist or doctor. Or you might want to study the bacteria which can ferment coarse seeds like soybeans to make a fine, tasty cheese-like food to add zest to the diets of all nations able to grow or buy soybeans.
What Bacteria Eat
There are hundreds of species of bacteria and it is possible to find a bacterium able to eat anything from sugar, to corn proteins, to soybean oil, to iron nails, to sulfur, to the compounds in wood. Yes, it is possible to find a bacterium able to do each of these. In fact, it has long been known that bacteria were involved in transforming soluble iron ions ( ) into the insoluble compounds of iron ores. Just as animals breathe oxygen to burn (oxidize) their food Thiobacillus(error not thibacillus) bacteria "breathe" (use) sulfur to oxidize their food. Each organism is using the named element as an electron acceptor to complete its electron transport pathway which generates ATP the high energy posphate that most organisms use for energy.
Most of them must find foods such as sugars, proteins and vitamins to live. The blue-green bacteria (some times called blue-green algae) have chlorophyll and can make their own food from light energy + carbon dioxide. Some other bacteria have red chlorophylls and can use light and carbon dioxide to make the sugars they need. Like all living things bacteria require mineral salts such as magnesium, calcium, iron, and others. Some bacteria are able to obtain the energy they need by oxidizing iron or sulfur. Some bacteria need sugars, vitamins, aminoacids, and other growth factors already digested and ready to use. Other bacteria can digest proteins down to amino acids and digest complex carbohydrates such as starches and table sugar down to simple sugars. Some bacteria can make their own amino acids and vitamins from carbohydrates. The metabolic abilities of bacteria are among the traits we use to group them into genera.
Bacteria species differ greatly in the conditions they need for growth. Some grow best in cool places such as soil or bodies of water, but others are able to grow in hot springs, hot water heaters, or undersea volcanoes. The bacteria which cause disease in mammals and birds, usually grow best at body temperatures. Many bacteria which cause diseases in hydra, snakes, turtles, and other cold-blooded animals, are not able to cause disease in birds or mammals because the high body temperatures kill these bacteria or limit their growth. This web site offers several pages of experiments to study the effect of pH, temperature, osmotic pressure (salt and sugar concentrations), oxygen concentration, and other environmental factors upon the growth of bacteria.
As you can imagine from this discussion, the numerous species of bacteria live in an astonishing variety of places and live on every food you can imagine. Some can eat gasoline and other
Lets begin our study of bacteria by considering the balance of nature. If there is food, some organism will eat it. If there is a place to live, some organism will live there. Every species has a great ability to produce offspring and its population expands until it runs out of food or it is limited by competition, its own waste products, or some other factor. Changes in climate or introduction of a new species from elsewhere can greatly affect the balance of nature. These simple sentences summarize the interactions of living things on earth.Bacteria are single-cell organisms and most of them must find foods such as sugars, proteins and vitamins to live. The blue-green bacteria (some times called blue-green algae) have chlorophyll and can make their own food from light energy + carbon dioxide. Some other bacteria have red chlorophylls and can use light and carbon dioxide to make the sugars they need. Like all living things bacteria require mineral salts such as magnesium, calcium, iron, and others. Some bacteria are able to obtain the energy they need by oxidizing iron or sulfur. Some bacteria need sugars, vitamins, aminoacids, and other growth factors already digested and ready to use. Other bacteria can digest proteins down to amino acids and digest complex carbohydrates such as starches and table sugar down to simple sugars. Some bacteria can make their own amino acids and vitamins from carbohydrates. The metabolic abilities of bacteria are among the traits we use to group them into genera.
Bacteria species differ greatly in the conditions they need for growth. Some grow best in cool places such as soil or bodies of water, but others are able to grow in hot springs, hot water heaters, or undersea volcanoes. The bacteria which cause disease in mammals and birds, usually grow best at body temperatures. Many bacteria which cause diseases in hydra, snakes, turtles, and other cold-blooded animals, are not able to cause disease in birds or mammals because the high body temperatures kill these bacteria or limit their growth. This web site offers several pages of experiments to study the effect of pH, temperature, osmotic pressure (salt and sugar concentrations), oxygen concentration, and other environmental factors upon the growth of bacteria.
As you can imagine from this discussion, the numerous species of bacteria live in an astonishing variety of places and live on every food you can imagine. Some can eat gasoline and other hydrocarbons. In fact, machinists face disagreeable odors on Monday morning from the accumulated waste products of microbes living in the cutting oils used to lubricate drills and cutting tools. We often say termites, cows, beavers, beetle larva, and other organisms can eat wood or sawdust. Actually, it is usually bacteria in their guts that eat the wood and the animal lives on the dead bacteria and substances they produce. In many instances, the bacteria actually live inside protozoa which live in the gut of the wood eating animal.
If some new substance comes along, a bacterium may have a little ability to eat it and that gives it a slight competitive edge because he can live when the others have run out of food. It may slightly outgrow his neighbors. Over time minor changes in genetic material occur which are called mutations. If these minor changes help an organism to grow better than its competitors, that organism may outgrow his neighbors. That is one reason the balance between living things on earth slowly changes. Mutations are constantly occurring. Nearly all mutations are harmful, meaning the change is not quite as good as the original, but some mutations give an organism an advantage over his neighbors. Genetics is the science of studying genetic material. Bacteria are good subjects for studying the basic laws of inheritance because they grow rapidly and and have traits which are easily studied.
Bacteria are important in food preparation and preservation. Firstly, many species would love to eat our food and we must find a way to keep them out or slow their growth. For example, foods retain their value longer when frozen because few bacteria can grow in a freezer, and the low temperature also slows biochemical reactions. Secondly, certain bacteria have specialized metabolisms which are ideal for food fermentations. For example, man has found many species which can digest sugars but not proteins. These species are very useful in food preparation if they produce acids which slow the growth of other organisms which would eat the proteins. Bacteria and yeasts which produce alcohols preserve foods because the alcohol kills other organisms or slows their growth. Primitive peoples around the world have developed an interesting variety of fermented foods: cheeses, drinks, breads, fish pastes, nut pastes, and others. These primitive foods sometimes cause disease because they contain pathogens such as TB, or toxic substances. Food microbiologists interested in producing safe versions of the primitive foods begin by isolating the microbes which cause the desired reactions and flavors. Then they add pure cultures of these organisms to clean raw food to produce safe, wholesome cheeses, breads, and other foods.
From the above, it is clear that the detailed study of bacteria may involve studying chemistry, botany, zoology, genetics, biochemistry, and other sciences. Even the use of mathematics and computers can enhance your bacteria science project. This web site will provide information and links to all those areas. Just begin something and let your interests lead you where they may.
Microbial safety precautions should be considered from the very beginning of your microbiology project. Most bacteria are harmless and many of those living on our skin help protect us and many species living in our gut are beneficial. For example, bacteria in the human gut produce vitamin K which is essential for normal clotting of blood.
Be sure to read our safety pages before you begin any experiments. Discuss your project with your parents and teachers and work out a safety plan before you begin. Helping your parents prepare and cook ordinary foods will give you valuable safety lessons because cuts, burns, and abrasions are the most common injuries in microbial projects.
Bacteria
