Acinetobacter baumannii: Difference between revisions
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==Cell structure and metabolism== | ==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. | |||
''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== | ==Ecology== | ||
Revision as of 14:24, 4 June 2007
A Microbial Biorealm page on the genus Acinetobacter baumannii
Classification
Higher order taxa
Bacteria; Proteobacteria; Gammaproteobacteria; Pseudomonadales; Moraxellaceae; Acinetobacter
Species
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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.
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
Describe any interactions with other organisms (included eukaryotes), contributions to the environment, effect on environment, etc.
Pathology
How does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.
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
Edited by student of Rachel Larsen and Kit Pogliano
