Bacterial Infections

Species of the genus Acinetobacter, except some of the A. lwoffii strain, grow very well on MacConkey agar. Most Acinetobacters are infectious, and the strain A.baumannii is the most common nosocomial infection in health care centers and military medical facilities. A. baumannii can cause infections including skin and wound infections and pneumonia. It also causes meningitis, but A. lwoffi is mostly responsible for that. A. baumannii can live on human skin or dry surfaces for weeks.

Since the start of the Iraq War, over 300 cases of A. baumannii had infected U.S. soldiers in the Middle East. At least five have died.

Ethanol has been found to stimulate the virulence of A. baumannii. Tests on infected nematode worms that were dosed with ethanol found that the worms laid fewer eggs and their life spans were only 80% of worms infected with a version of A. baumannii that didn't respond to ethanol. This study suggests that the common misconception that drinking alcohol kills infections is false and drinking alcohol may actually help the infection to grow. (Smith & Snyder, 2005)

In November, 2004, the CDC reported an increasing number of A. baumannii bloodstream infections in patients at military medical facilities in which service members injured in the Iraq/Kuwait region during Operation Iraqi Freedom (OIF) and in Afghanistan during Operation Enduring Freedom (OEF) were treated. Most of these were multidrug-resistant. Among one set of isolates from Walter Reed Army Medical Center, 13 (35%) were susceptible to imipenem only, and two (4%) were resistant to all drugs tested. One antimicrobial agent, colistin (polymyxin E), has been used to treat infections with multidrug-resistant A. baumannii; however, antimicrobial susceptibility testing for colistin was not performed on isolates described in this report. Because A. baumannii can survive on surfaces for up to 20 days, they pose a high risk of spread and contamination in hospitals, potentially putting immune-compromised and other patients at risk for drug resistant infections that are often fatal and generally expensive to treat.

Introduction

Bacteria of the genus Acinetobacter are widespread in nature, and can be recovered from water, soil and living organisms. They are non-motile, coccobacillary, strictly aerobic and Gram-negative; they can use a variety of carbon sources for growth, and can be cultured on relatively simple media, including trypticase soya agar or nutrient agar. Extensive reviews of the genus have been written by Juni (15) and by Bergogne-Bérézin & Towner (1). Strains of A. baumannii, and the unnamed groups 3 and 13 TU are recovered predominantly from clinical specimens, with A. baumannii being notorious for its capacity to colonise and infect severely ill, hospitalised patients. Strains of this genomic species can persist in hospitals and give rise to outbreaks; they are usually highly resistant to antibiotics, which makes them difficult to eradicate.

Two recently described species, A. ursingii ('phenon 1') and A. schindlerii ('phenon 2') (17, 18) are also associated with patients; thus A. ursingii was cultured from the blood of severely ill hospitalised patients, and A. schindlerii from non-sterile body sites of outpatients. Most other (genomic) species of Acinetobacter have been found in different environments, e.g. strains of A. calcoaceticus are isolated predominantly from soil and A. johnsonii from activated sludge and frozen food, although representatives of these and other species have also been recovered occasionally from human specimens. Strains of A. venetianus, including the emulsan-producing strain RAG-1, have been found in seawater and oil-degrading consortia (7, 22). Overall, the natural habitats of most Acinetobacter (genomic) species have not been well-studied.

Within the context of ENEMTI, the Acinetobacter Working Group will seek to develop two different protocols that can be used for the development of an interactive database for the exchange of microbial typing database:-

(i) a high-resolution typing method suitable for use in reference laboratories: AFLP protocol

(ii) a simpler rapid typing method for use in routine hospital laboratories: RAPD method

The ENEMTI initiative aims to harmonise typing methods so that the fingerprints generated can be used to set up electronic databanks by which the geographic spread of particular strains can be depicted and monitored.
ENEMTI participants have also collaborated with members of the EU ARPAC Concerted Action ('Antibiotic Resistance Prevention and Control') to develop an Acinetobacter database based on pulsed-field gel electrophoresis (PFGE) fingerprint profiles. Click here to enter the Acinetobacter PFGE database.
More information on the genus Acinetobacter, a heterogeneous group of organisms.

Taxonomy

Currently, the genus Acinetobacter comprises at least 23 genomic species (DNA-DNA hybridisation groups; DNA groups), 10 of which have been given species names; other DNA groups are designated by numbers (for Table 1, see the original Word document). The numbers 13-15 have been given to sets of strains in two independent studies (6, 20); DNA group 13 of Bouvet & Jeanjean (BJ) has been found to correspond to group 14 of Tjernberg & Ursing (TU), whereas no correlation was found for the two other groups. Strains of A. calcoaceticus, A. baumannii, and the unnamed groups 3 and 13TU are genetically closely related and difficult to separate phenotypically, and are therefore sometimes unified in the so-called A. calcoaceticus – A. baumannii (Acb) complex (10). Apart from the known genomic species, additional strains have been found, some of which are closely related to the Acb complex (12), while the taxonomic status of others has not yet been resolved.

Genus identification

Bacteria can be identified to the genus Acinetobacter by the phenotypic criteria listed in Table 2 (see the original Word document). A simple test for identification to the genus Acinetobacter is based on the finding that DNA of organisms belonging to the genus can be used to transform an auxotrophic Acinetobacter strain (BD413 trpE27) to prototrophy (14).

(Genomic) species identification

DNA-DNA hybridisation is the gold standard for identification of Acinetobacter strains, but this method is not applicable in most laboratories. A phenotypic identification scheme, including enzymatic and nutritional tests and growth at different temperatures, was devised by Bouvet & Grimont (4, 5). Several studies have shown that some genomic species are difficult to identify by phenotypic tests (10, 16). Similarly, commercial phenotypic identification systems, such as API 20NE and Biolog, show only moderate performance (2, 3). In particular, A. baumannii, DNA groups 3 and 13TU are difficult to differentiate by these systems.
Several genotypic methods have been proposed for identifying acinetobacters to the genomic species level, including ribotyping (11), tDNA fingerprinting (9), amplified ribosomal DNA restriction analysis (ARDRA) (8, 21), and AFLP (13). An overview of ARDRA patterns for species identification can be found here

Despite the progress made in subdividing the genus Acinetobacter and the efforts to develop easy identification methods, identification to the genomic species level can still be problematic. This may be overcome by using a combination of methods, which results in a so-called 'consensus identification' (17).

Typing of Acinetobacter strains

Virtually all currently available typing methods have been used for discrimination of acinetobacters below the species level. Phenotypic methods, including biotyping, cell envelope protein electrophoresis, and quantitative antibiogram typing were applied successfully in the 1980s and 1990s. More recently, genotypic methods including plasmid typing (now rarely used), ribotyping, pulsed-field gel electrophoresis (PFGE), PCR fingerprinting and AFLP analysis have been used in numerous studies. In general, a combination of typing methods is recommended for unambiguous strain identification in local situations.

References

Bergogne-Bérézin E & Towner KJ (1996). Acinetobacter spp. as nosocomial pathogens: microbiological, clinical, and epidemiological features. Clin Microbiol Rev 9, 148-165.
Bernards AT, Dijkshoorn L, van der Toorn J, Bochner BR & van Boven CPA (1995). Phenotypic characterization of Acinetobacter strains of 13 DNA-DNA hybridization groups by means of the Biolog system. J Med Microbiol 42, 113-119.
Bernards AT, van der Toorn J, van Boven CPA. & Dijkshoorn L (1996). Evaluation of the ability of the API 20NE system to identify Acinetobacter genomic species. Eur J Clin Microbiol Infect Dis 15, 303-308.
Bouvet PJM & Grimont PAD (1986). Taxonomy of the genus Acinetobacter with the recognition of Acinetobacter baumannii sp. nov., Acinetobacter haemolyticus sp. nov., Acinetobacter johnsonii sp. nov., and Acinetobacter junii sp. nov., and emended descriptions of Acinetobacter calcoaceticus and Acinetobacter lwoffii. Int J Syst Bacteriol 36, 228-240.
Bouvet PJM & Grimont PAD (1987). Identification and biotyping of clinical isolates of Acinetobacter. Ann Inst Pasteur/Microbiol 138, 569-578.
Bouvet PJM & Jeanjean S (1989). Delineation of new proteolytic genomic species in the genus Acinetobacter. Res Microbiol 140, 291-299.
DiCello F, Pepi M, Baldi F & Fani R (1997). Molecular characterization of an n-alkane-degrading bacterial community and identification of a new species, Acinetobacter venetianus. Res Microbiol 148, 237-249.
Dijkshoorn L, van Harsselaar B, Tjernberg I, Bouvet PJM & Vaneechoutte M (1998). Evaluation of amplified ribosomal DNA restriction analysis for identification of Acinetobacter genomic species. Syst Appl Microbiol 21, 33-39.
Ehrenstein B, Bernards AT, Dijkshoorn L, Gerner-Smidt P, Towner KJ, Bouvet PJ, Daschner FD & Grundmann H (1996). Acinetobacter species identification by using tRNA spacer fingerprinting.J Clin Microbiol 34, 2414-2420.
Gerner-Smidt P, Tjernberg I & Ursing J (1991). Reliability of phenotypic tests for identification of Acinetobacter species. J Clin Microbiol 29, 277-282.
Gerner-Smidt P (1992). Ribotyping of the Acinetobacter calcoaceticus-Acinetobacter baumannii complex. J Clin Microbiol 30, 2680-2685
Gerner-Smidt P & Tjernberg I (1993). Acinetobacter in Denmark: II. Molecular studies of the Acinetobacter calcoaceticus- Acinetobacter baumannii complex. APMIS 101, 826-832.
Janssen P, Maquelin K, Coopman R, Tjernberg I, Bouvet P, Kersters K & Dijkshoorn L (1997). Discrimination of Acinetobacter genomic species by AFLP fingerprinting. Int J Syst Bacteriol 47, 1179-1187.
Juni E (1972). Interspecies transformation of Acinetobacter: Genetic evidence for a ubiquitous genus. J Bacteriol 112, 917-931.
Juni E (1984). Genus III Acinetobacter Brisou and Prévot 1954, 727 AL. In: Bergey’s Manual of Systematic Bacteriology vol. 1, Krieg, N.R. (ed). Williams and Wilkins, Baltimore, pp 303-307.
Kämpfer P, Tjernberg I & Ursing J (1993). Numerical classification and identification of Acinetobacter genomic species. J Appl Bacteriol 75, 259-268.
Nemec A, Dijkshoorn L & Ješek P (2000). Recognition of two novel phenons of the genus Acinetobacter among glucose non-acidifying isolates from human specimens. J Clin Microbiol 38, 3937-3941.
Nemec A, De Baere T, Tjernberg I, Vaneechoutte M, van der Reijden TJK & Dijkshoorn L (2001). Acinetobacter ursingii sp.nov. and Acinetobacter schindleri sp. nov., isolated from human clinical specimens. Int J Syst Evol Microbiol, in press.
Nishimura Y, Ino T & Iizuka H (1988). Acinetobacter radioresistens sp. nov. isolated from cotton and soil. Int J Syst Bacteriol 38, 209-211.
Tjernberg I & Ursing J (1989). Clinical strains of Acinetobacter classified by DNA-DNA hybridization. APMIS 97, 595-605.
Vaneechoutte M, Dijkshoorn L, Tjernberg I, Elaichouni A, de Vos P, Claeys G & Verschraegen G (1995). Identification of Acinetobacter genomic species by amplified ribosomal DNA restriction analysis. J Clin Microbiol 33, 11-15.
Vaneechoutte M, Tjernberg I, Baldi F, Pepi M, Fani R, Sullivan ER, van der Toorn J & Dijkshoorn L (1999). Oil-degrading Acinetobacter strain RAG-1 and strains described as 'Acinetobacter venetianus' sp. nov. belong to the same genomic species. Res Microbiol 150, 69-73.

# posted by Pat O'Connor @ 6:21 AM