Acinetobacter baumannii: Difference between revisions

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Efflux pumps located in the cell membrane are used to pump chemicals and antibiotics out of the cell.  Efflux pumps in ''A. baumannii'' include resistance to tetracycline called Tet (A) and Tet (B), part of the major facilitator superfamily (MFS) functions in the exchange of protons and tetracycline.  There is also resistance-nodulation-cell division (RND) efflux pumps found in the strain ''A. baumannii'' BM4454 that is encoded by the gene adeB which provides aminoglycoside resistance.
Efflux pumps located in the cell membrane are used to pump chemicals and antibiotics out of the cell.  Efflux pumps in ''A. baumannii'' include resistance to tetracycline called Tet (A) and Tet (B), part of the major facilitator superfamily (MFS) functions in the exchange of protons and tetracycline.  There is also resistance-nodulation-cell division (RND) efflux pumps found in the strain ''A. baumannii'' BM4454 that is encoded by the gene adeB which provides aminoglycoside resistance.


The cell wall on ''A. baumannii'' is not static, but rather changes in response to environmental conditions.  In one study it was discovered that when placed in dry conditions there was a 30% increase in the thickness of the cell wall, caused by a change in distance of the outer membrane and plasma membrane or periplasmic gel.  Also, there was a change in the shape of ''A. baumannii'' from rod shaped to cocci by decreasing cell division, in response to desication.   
The cell wall on ''A. baumannii'' is not static, but rather changes in response to environmental conditions.  In one study it was discovered that when placed in dry conditions there was a 30% increase in the thickness of the cell wall, caused by a change in distance of the outer membrane and plasma membrane or periplasmic gel.  Also, there was a change in the shape of ''A. baumannii'' from rod shaped to cocci by decreasing cell division in response to desication.   


''A. baumanni'' is a glucose-non-fermentative, oxidase negative, aerobic bacteria.  Antibiotic resistant strains of ''A. baumannii'' produce beta-lactamases which can prevent antibiotic function by hydrolyzing penicillins, cephalosporins, and carbapenems.  One of the first beta-lactamases, called ARI-1, but later changed to OXA-23 was collected in 1985 in Scotland, which hydrolyzed carbapenem.  Other OXA-type beta-lacamases include OXA-24 and OXA-58.
''A. baumanni'' is a glucose-non-fermentative, oxidase negative, aerobic bacteria.  Antibiotic resistant strains of ''A. baumannii'' produce beta-lactamases which can prevent antibiotic function by hydrolyzing penicillins, cephalosporins, and carbapenems.  One of the first beta-lactamases, called ARI-1, but later changed to OXA-23 was collected in 1985 in Scotland, which hydrolyzed carbapenem.  Other OXA-type beta-lacamases include OXA-24 and OXA-58.

Revision as of 15:14, 4 June 2007

A Microbial Biorealm page on the genus Acinetobacter baumannii

Classification

Acinetobacter baumannii,Photo credit: Janice Carr, CDC

Higher order taxa

Bacteria; Proteobacteria; Gammaproteobacteria; Pseudomonadales; Moraxellaceae; Acinetobacter

Species

NCBI: Taxonomy

Acinetobacter baumannii

Description and significance

Acinetobacter baumannii, previously named Acinetobacter calcoaceticus, is an opportunistic pathogen found in soil and water. One of the first Acientobacter found in soil was discovered in 1911 by M.W. Beijerinck. In the 1970s A. baumannii was susceptible to common antibiotics, but has now developed into a multidrug-resistant bacteria, capable of acquiring resistant genes. One of the first antibiotic resistant strains of A. baumannii called carbapenem-resistant A. baumannii (CRAB) was isolated in May 1998 from a leukemia patient. A. baumanni generally affects patients with low immune systems, which has caused nosocomial infections and major concerns in hospitals given the ability of A. baumannii to live on a variety of hospital surfaces such as surgical drains and catheters. Recently, there has been a growing number of blood stream infections caused by multidrug resitant A. baumanni among service members of the Iraq and Afghanistan military operations: Operation Iraqi Freedom and Operation Enduring Freedom, respectively. Blood stream infections caused by A. buamnni include pneumonia, urinary tract infections, and septicaemia. Since A. buamanni has become more difficult to treat due to its increasing resitance to antibiotics such as carbapenem, beta-lactam, and tetracycline understanding its genomic sequence is essential to effectively treat infections and preventing A. buamanni transfer and growth on hospital surfaces.

Genome structure

A.baumannii is comprised of a single circular chromosome that contains 3,976,747 base pairs in which 3,454 are used for protein coding. One strain of A. baumannii called AYE contains an 86kb resistance island, called AbaR1, which contains 45 resistance genes and is currently the largest island known to date. A resistance island is a section on a chromosome that contains genes necessary to code for antibiotic resistance. Of those 45 resistance genes, 25 genes code for resistance against many antibiotics such as: tetracycline, aminoglycosides, cotrimoxazole, and chloramphenicol. Not only did the resistance island code against antibiotics, but also operons for arsenic and mercury resistance. There are 14 resistance genes that code for class 1 integrons, which are sections of the chromosome capable of recombination, expression, and integration. Mobility elements, such as transposase were found on 22 ORFs (open reading frames).A. baumanni AYE has three plasmids, but none contain resistance markers. Not only does the strain AYE contain resistance genes, but also a common amino acid sequence with other organisms, which demonstrates genetic exchange, where “39 genes (44%) are likely to have originated from Pseudomonas spp., 30 (34%) from Salmonella spp., 15 (17%) from Escherichia spp., and four (4%) from other microorganisms”

Cell structure and metabolism

A. baumannii is an encapsulated Gram-negative coccobacilli bacteria that is generally non-motile. Features on the outer cell membrane include porins and efflux channels which contribute to antibiotic resistance. In general, porins are protein channels that allow the transport of molecules across the membrane and are also sites of attachment for antibiotics. However, porins on A. baumannii are fewer and smaller than other Gram-negative bacteria, thereby decreasing cell permeability and increasing antibiotic resistance. Interestingly, less than 5% of molecules are permeable to the cell membrane, which is less than that found in Escherichia coli. In some studies it was found that resistance to the antibiotic, carbapenem, was the result of the lack of a 29kDa outer membrane protein gene called carO. It is believed that the protein CarO is involved with the import of carbapenem into the cell.

Efflux pumps located in the cell membrane are used to pump chemicals and antibiotics out of the cell. Efflux pumps in A. baumannii include resistance to tetracycline called Tet (A) and Tet (B), part of the major facilitator superfamily (MFS) functions in the exchange of protons and tetracycline. There is also resistance-nodulation-cell division (RND) efflux pumps found in the strain A. baumannii BM4454 that is encoded by the gene adeB which provides aminoglycoside resistance.

The cell wall on A. baumannii is not static, but rather changes in response to environmental conditions. In one study it was discovered that when placed in dry conditions there was a 30% increase in the thickness of the cell wall, caused by a change in distance of the outer membrane and plasma membrane or periplasmic gel. Also, there was a change in the shape of A. baumannii from rod shaped to cocci by decreasing cell division in response to desication.

A. baumanni is a glucose-non-fermentative, oxidase negative, aerobic bacteria. Antibiotic resistant strains of A. baumannii produce beta-lactamases which can prevent antibiotic function by hydrolyzing penicillins, cephalosporins, and carbapenems. One of the first beta-lactamases, called ARI-1, but later changed to OXA-23 was collected in 1985 in Scotland, which hydrolyzed carbapenem. Other OXA-type beta-lacamases include OXA-24 and OXA-58.

Ecology

A. baumannii is able to survive on various conditions in the hospital that include abiotic,wet, or dry surfaces. A. baumannii has the ability to avoid desiccation for more than 30 days on dry surfaces, although survival rate depends on where the specific strain originally came from (e.g. wet or dry conditions). One strain of A. baumannii, 19606 is capable of forming biofilm on glass and plastic surfaces via pili formation. The production of biofilm explains how A. baumanni can survive in different environmental factors found in the hospitals, including static conditions such as bed sheets and furniture, while also capable of living in harsh conditions such as catheters and respiratory tubes. A. baumanni also produced exopolysaccharides which strengthen the biofilm.

Pathology

Acinetobacter baumannii causes 2-10% of all Gram-negative infections in the U.S. and Europe, poses little risk to healthy individuals, but generally causes infections to those with weakened immune systems. Specifically, the intensive care unit (ICU) in hospitals houses patients with susceptible immune systems and is normally equipped with ventilators and invasive equipment such as catheters, are factors that cause A. baumannii infections such as pneumonia, meningitis, septicemia, and urinary and respiratory tract infections. In one study, it was shown that A. baumannii could cause apoptosis or cell death to human laryngeal epithelial cells via an outer membrane protein (OMP 38). OMP38 releases cytochrome c and an apoptosis-inducing factor which enters the epithelial cell nucleus and causes the degradation of DNA (180bp). The ability of A. baumannii to cause untreatable infections is due to a variety of antibiotic resistance genes and cell surface structures that prevent the influx of antibiotics (see cell surface structure and metabolism). Since A. buamannii is commonly found in hospitals which is an environment where “antibiotics are frequently used, possessing integrons with multiple resistance determinants confers a strong selective advantage”

Application to Biotechnology

Does this organism produce any useful compounds or enzymes? What are they and how are they used?

Current Research

Enter summaries of the most recent research here--at least three required

References

[Sample reference] Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "Palaeococcus ferrophilus gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". International Journal of Systematic and Evolutionary Microbiology. 2000. Volume 50. p. 489-500.

Edited by student of Rachel Larsen and Kit Pogliano