Sunday, December 04, 2005


Pseudomonas aeruginosa

Pseudomonas aeruginosa

Pseudomonas aeruginosa is widely distributed in soil, water, sewage and plants, and is a common human intestinal bacterium. It also causes disease in humans, certain animals, insects and plants. Infection is usually restricted to hospitalised patients with predisposing conditions (it causes 14% of all nosocomial infections) but it is also associated with 5% of all community-acquired infections.

Perhaps the most commonly encountered infection outside hospitals is otitis externa ('swimmer's ear'), of which Pseudomonas aeruginosa causes 35-70%. This can usually be treated satisfactorily with aural toilet without resorting to antibiotics but, particularly in diabetics, malignant otitis externa and otitis media can occur and can be life-threatening in extreme cases, especially when extension to the cranial parameningeal deep fascial space occurs.

With the ever-increasing use of contact lenses, eye infections with P.aeruginosa are becoming more and more common. These range from purulent conjunctivitis to iridocyclitis, keratitis and iritis, corneal ulcer, and panophthalmitis, and can be sight-threatening. Refer to a previous Newsletter for details.

Wound infections are common but are frequently part of a mixed flora and often do not require specific antibiotic treatment, responding to local measures and the removal of such pathogens as Staphylococcus aureus if present. Surgical wounds and other deep or severe trauma may be exceptions.

Foot puncture wounds in children are prone to P.aeruginosa infection and can lead to septic arthritis and endocarditis. Intravenous drug abusers are even more prone to such infections, with P.aeruginosa causing 14% of endocarditis in such people.

Extensive or deep burns are also susceptible to infection with P.aeruginosa. This can usually be satisfactorily treated with a local antibiotic, such as silver sulphadiazine.

Skin infections are of two types. Pyoderma form when the organism colonises, and subsequently invades (especially when occlusive dressings are used), exfoliative lesions, venous stasis ulcers or eczema. These have a characteristic moth-eaten appearance and erythematous border. The process can be acute and invasive or chronic indolent. In the latter case, a slowly progressive, burrowing inflammation forms coalescent papulopustular lesions covered with a malodorous crust. Long term oral ciprofloxacin is usually used in treatment.

The second type is a folliculitis, consisting of discrete, maculopapular lesions a few mm in diameter, which develop a vesicle or pustule on their apices. These occur on the trunk or proximal extremities, predominately axillae and pelvis and are typically associated with spa use. A similar condition, characterised by exquisitely tender erythematous plantar nodules and labelled 'Pseudomonas hot foot syndrome' by the physicians who reported it, recently occurred as an outbreak traced to a wading pool. These conditions do not require antibiotics and are adequately treated with simple non-specific topical measures.

P.aeruginosa sinusitis is usually a result of lavage of one kind or another with contaminated water or saline. Resolution may require surgical intervention as well as antibiotic therapy.
Lower respiratory tract infections with P.aeruginosa are associated with cystic fibrosis and other chronic lung conditions and with invasive hospital procedures. Infections affecting cystic fibrosis patients are frequently due to mucoid 'strains'. It was thought that these organisms were distinct strains but research has shown that non-mucoid strains can become mucoid and vice versa and that mucoidicity is basically an indicator of long-term residence at the site. Such strains are also encountered in long-standing urinary tract infections. P.aeruginosa urinary tract infections are almost invariably the result of invasive procedures.

P.aeruginosa is also commonly isolated from sputum specimens from 'normal' patients who have been extensively treated with antibiotics. In most cases, the best response is to withdraw or withhold antibiotic treatment; these isolations usually represent colonisation and rarely proceed to frank infection. This applies to non-mucoid isolates; isolation of mucoid 'strains' may indicate that the patient is not normal and may require further investigation.

Nosocomial infections with P.aeruginosa cover the entire gamut. The organism is responsible for 5% of surgical wound infections, 8% of thrombophlebitis and is an important cause of fatal bacteremia in neutropenic patients.

Patients with granulocytopenia, defects in opsonophagocytic antibodies, local immunity or depressed or defective cell-mediated immunity or with interrupted integument are especially prone to infection with P.aeruginosa.

P.aeruginosa has natural resistance to many antibiotics, including all penicillins except ticarcillin (13% resistance in Australia) and piperacillin (9% resistance in Australia), all cephalosporins except ceftazidime (10% resistance in Australia), cefipime and cefpirome, and trimethoprim, cotrimoxazole and tetracyclines. Gentamicin (17% resistance in Australia) and tobramycin (8% resistance in Australia) remain the favoured agents for hospital use but oral norfloxacin (UTI's only) and ciprofloxacin are most widely used in outpatients. Resistance to the latter two agents is now 37-38% in the USA but 8-13% in Australia. Imipenem is occasionally used in hospitals (17% resistance in Australia). Colistin and neomycin are sometimes used topically and colistin is rarely used systemically as a drug of last resort.

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Pseudomonas Aeruginosa Infections

Last Updated: October 28, 2004

Synonyms and related keywords: swimmer's ear, Shanghai fever, tropical immersion foot syndrome, green nail syndrome, green foot, Pseudomonas hot-foot syndrome

Author: Samer Qarah, MD, Pulmonary Critical Care Consultant, Department of Internal Medicine, Division of Pulmonary and Critical Care, The Brooklyn Hospital Center and Cornell University

Coauthor(s): Burke A Cunha, MD, Professor of Medicine, State University of New York at Stony Brook School of Medicine; Chief, Infectious Disease Division, Winthrop-University Hospital; Pratibha Dua, MD, Staff Physician, Department of Internal Medicine, The Brooklyn Hospital Center; Klaus-Dieter Lessnau, MD, FCCP, Clinical Assistant Professor of Medicine, New York University School of Medicine; Medical Director, Pulmonary Physiology Laboratory, Department of Medicine, Section of Pulmonary Medicine, Lenox Hill Hospital

Background: Pseudomonas is a gram-negative rod belonging to the family Pseudomonadaceae. More than half of all clinical isolates produce the blue-green pigment pyocyanin. These pathogens are widespread in nature, inhabiting soil, water, plants, and animals (including humans). Pseudomonas aeruginosa has become an important cause of infection, especially in patients with compromised host defense mechanisms. It is the most common pathogen isolated from patients who have been hospitalized longer than 1 week. It is a frequent cause of nosocomial infections such as pneumonia, urinary tract infections (UTIs), and bacteremia. Pseudomonal infections are complicated and can be life threatening.

Pathophysiology: P aeruginosa is an opportunistic pathogen. It rarely causes disease in healthy persons. In most cases of infection, loss of the integrity of a physical barrier to infection (eg, skin, mucous membrane) usually occurs or underlying immune deficiency (eg, neutropenia, immunosuppression) usually is present. Adding to its pathogenicity, this bacterium has minimal nutritional requirements and can tolerate a wide variety of physical conditions.

The pathogenesis of pseudomonal infections is multifactorial and complex. Pseudomonas is both invasive and toxigenic. The 3 stages, according to Pollack (2000), are (1) bacterial attachment and colonization, (2) local infection, and (3) bloodstream dissemination and systemic disease.

The importance of colonization and adherence is most evident when studied in the context of respiratory tract infections in patients with cystic fibrosis and in those that complicate mechanical ventilation.


In the US: According to US Centers for Disease Control and Prevention (CDC) data collected from 1990-1996, P aeruginosa was the second most common cause of nosocomial pneumonia (17% of isolates), the third most common cause of UTI (11%), the fourth most common cause of surgical site infections (8%), the seventh most common isolated pathogen from the bloodstream (3%), and the fifth most common isolate overall (9%)—obtained from all sites.

Internationally: P aeruginosa is very common in patients with diabetes who are immunocompromised


All infections caused by P aeruginosa are treatable and potentially curable. Acute fulminant infections, such as bacteremic pneumonia, sepsis, burn wound infections, and meningitis, are associated with extremely high mortality.

Race: P aeruginosa endocarditis in individuals who abuse intravenous (IV) drugs is observed mainly among young black males.

Sex: Cases of endocarditis and vertebral osteomyelitis have been observed in young males who use IV drugs.


Vertebral osteomyelitis resulting from a pseudomonal infection mainly occurs in elderly patients and often involves the lumbosacral spine. Young people who use IV drugs also may be affected.

Involvement of the GI tract most commonly occurs in infants and patients with hematologic malignancies and neutropenia that has resulted from chemotherapy.

The incidence of pseudomonal pneumonia in patients with cystic fibrosis has shown a shift towards patients who are older than 26 years.


History: Pseudomonal infections can involve any part of the body.

Respiratory tract

Pneumonia is observed in patients with immunosuppression and chronic lung disease. It can be acquired nosocomially in the intensive care unit (ICU) setting and is associated with positive-pressure ventilation and endotracheal tubes. The pneumonia may be primary and follow aspiration of the organism from the upper respiratory tract, especially in patients on mechanical ventilation. Alternatively, it may occur as a result of bacteremic spread to the lungs. This is observed commonly in patients following chemotherapy-induced neutropenia.

Bacteremic pneumonia occurs in patients with neutropenia following chemotherapy and in patients with AIDS.

Chronic infection of the lower respiratory tract with P aeruginosa is prevalent among patients with cystic fibrosis. These patients may present with chronic productive cough, anorexia, weight loss, wheezing, and tachypnea.

Symptoms of pneumonia include fever, chills, severe dyspnea, cyanosis, productive cough, confusion, and other signs of a systemic inflammatory response.


Bacteremia may be acquired via medical devices in hospitals and nursing homes, and the mortality rate remains greater than 10%.

Signs and symptoms depend on the primary site of infection.


P aeruginosa may infect native heart valves in individuals who abuse IV drugs, and it also may infect prosthetic heart valves.

Right-sided and left-sided valve infections may occur.

Nonspecific symptoms include fever and malaise, with more specific symptoms depending on which cardiac valve is involved. Left-sided endocarditis typically presents with symptoms of congestive heart failure and those resulting from systemic spread of septic emboli.

Central nervous system

P aeruginosa can cause meningitis and brain abscess.

Most infections follow an extension from a contiguous parameningeal structure, such as an ear, a mastoid, paranasal sinus surgery, or diagnostic procedures. In some patients, the involvement of the CNS is due to hematogenous spread of the organism from infective endocarditis, pneumonia, or UTI.

Patients present with fever, headache, and confusion. The onset may be fulminant or subacute, often depending on the immune status of the patient.


In external otitis (swimmer's ear), patients present with pain, pruritus, and ear discharge. The pain is worsened by traction on the pinna.

Pseudomonas is a common cause of chronic otitis media. Malignant otitis externa is a manifestation of invasive infection predominantly observed in patients with uncontrolled diabetes. It begins as ordinary otitis externa that fails to respond to antibiotic therapy.

Presenting symptoms are persistent pain, edema, and tenderness of the soft tissues of the ear, with a purulent discharge. Fever is uncommon, and some patients present with a facial nerve palsy. Extension of the infection to the temporal bone can result in osteomyelitis, and further extension can create cranial nerve palsies and possibly a CNS infection.


The cornea, aqueous humor, and vitreous humor comprise an immunocompromised environment, and Pseudomonas, when introduced, produces extracellular enzymes that cause a rapidly progressive and destructive lesion. P aeruginosa is a common cause of bacterial keratitis, scleral abscess, and endophthalmitis in adults and ophthalmia neonatorum in children.

Predisposing conditions for corneal involvement are trauma, contact lens use, predisposing ocular conditions, exposure to an ICU environment, and AIDS. Corneal lesions can progress to endophthalmitis and orbital cellulitis. Symptoms are pain, redness, swelling, and impaired vision.

Bones and joints

The most common sites of involvement are the vertebral column, the pelvis, and the sternoclavicular joint.

Infection may be blood-borne, as in individuals who abuse IV drugs or in patients with pelvic infections or UTI. Alternatively, the infection may be contiguous, related to penetrating trauma, surgery, or overlying soft tissue infections. Patients at risk for pseudomonal bone and joint infections include those with puncture wounds to the foot, peripheral vascular disease, IV drug abuse, or diabetes mellitus.

Vertebral osteomyelitis may involve the cervical spine, and patients present with neck or back pain lasting weeks to months. Occasionally, patients with complicated UTI may develop lumbosacral vertebral osteomyelitis.

Patients with pyoarthrosis present with swelling and pain in the affected joint. Patients persistently are febrile.


Pseudomonal infections can affect every portion of the GI tract. The disease often is underestimated but, most commonly, it affects very young children and adults with hematologic malignancies and chemotherapy-induced neutropenia. Additionally, colonization of the GI tract is an important portal of entry for pseudomonal bacteremia in patients who are neutropenic.

The spectrum of disease can range from very mild symptoms to severe necrotizing enterocolitis with significant morbidity and mortality.

Epidemics of pseudomonal diarrhea can occur in nurseries. Young infants may present with irritability, vomiting, diarrhea, and dehydration.

The infection can cause enteritis, with patients presenting with prostration, headache, fever, and diarrhea (Shanghai fever).

Pseudomonas typhlitis typically presents in patients with neutropenia resulting from acute leukemia, with a sudden onset of fever, abdominal distension, and worsening abdominal pain.

Urinary tract infections

Pseudomonal infections of the urinary tract usually are hospital-acquired and iatrogenic, related to catheterization, instrumentation, and surgery.

These infections can involve the urinary tract through an ascending infection or through bacteremic spread and are a frequent source of bacteremia.

No specific characteristics distinguish this type of infection from other forms of UTI.


Pseudomonas does not grow on dry skin, but it flourishes on moist skin.

Green nail syndrome is a paronychial infection that can develop in individuals whose hands frequently are submerged in water.

Secondary wound infections occur in patients with decubiti, eczema, and tenia pedis. These infections may have a characteristic blue-green exudate with a fruity odor.

Pseudomonas is a common cause of hot tub or swimming pool folliculitis. Patients can present with pruritic follicular, maculopapular, vesicular, or pustular lesions on any part of the body that was immersed in water. Pseudomonal bacteremia produces distinctive skin lesions known as ecthyma gangrenosum.

Pseudomonas also has emerged as an important source of burn wound sepsis. Invasive burn wound sepsis is defined as the bacterial proliferation of 100,000 organisms per gram of tissue, with subjacent involvement of subjacent unburned tissue.



Fever is present and may respond to antibiotics, despite the presence of bacteremia.
A new onset of cardiac murmur or a change in character of a preexisting murmur may develop.
Peripheral signs of thromboembolism, such as Janeway lesions, Osler nodes, and ecthyma gangrenosum, may occur.


Patients have rales, rhonchi, fever, cyanosis, retractions, and relative bradycardia.

Shock may develop in patients with bacteremic pneumonia.

Patients with cystic fibrosis may reveal clubbing, increased anteroposterior (AP) diameter, and malnutrition.

Gastrointestinal tract

Young infants with diarrhea may have fever, signs of dehydration, abdominal distension, and signs of peritonitis.

Physical findings of Shanghai fever may include fever, splenomegaly, and rose spots. Depending on the severity of the illness, prostration, dehydration, and vascular collapse may be observed.

Skin and soft tissue infections

Ecthyma gangrenosum lesions are hemorrhagic and necrotic, with surrounding erythema. These characteristic lesions almost always are caused by Pseudomonas and usually are found in the axilla, groin, or perianal area but may involve any part of body.

Subcutaneous nodules, deep abscesses, cellulitis, and fasciitis also may occur.

Pseudomonal burn wound infections appear black or as a violaceous discoloration or eschar.

Systemic manifestations of burn wound sepsis may include fever or hypothermia, disorientation, hypotension, oliguria, ileus, and leukopenia.

Bone and joint infections

Vertebral osteomyelitis reveals local tenderness and a decreased range of motion.

Neurological deficits, when present, are mild.

With eye infections, the physical examination reveals lid edema, conjunctival erythema and chemosis, and severe mucopurulent discharge adherent to an underlying corneal ulcer.

Malignant otitis externa

The external auditory canal is erythematous, swollen, inflamed, and has discharge.
The tympanic membrane is hidden from view because of edema and may be ruptured.

Local lymphadenopathy may be present.


Patients have fever, tachypnea, and tachycardia.

Hypotension and shock may develop.

Jaundice may occur.

Skin shows characteristic skin lesions called ecthyma gangrenosum.


Pseudomonal bacteremia occurs in malignancy, chemotherapy, AIDS, burn wound sepsis, and diabetes.

Certain populations of patients are especially susceptible to pseudomonal infections.

Predisposing conditions include placement of IV lines, severe burns, urinary tract catheterization, surgery, trauma, and premature birth (infants).

Conditions predisposing to pseudomonal infections (ie, type of infection most prevalent in that condition)

Diabetes - Malignant otitis externa
Drug addiction - Endocarditis, osteomyelitis
Leukemia - Sepsis, typhlitis
Cancer - Pneumonia, sepsis
Burn wound - Cellulitis, sepsis
Cystic fibrosis - Pneumonia
Surgery involving CNS - Meningitis
Tracheostomy - Pneumonia
Neonatal period - Diarrhea
Corneal ulcer - Panophthalmitis


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