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Acinetobacter
Acinetobacter baumannii
Scientific classification
Kingdom: Bacteria
Phylum: Proteobacteria
Class: Gammaproteobacteria
Order: Pseudomonadales
Family: Moraxellaceae
Genus: Acinetobacter
Brisou & Prévot 1954
Species

Acinetobacter baumannii
Acinetobacter baylyi
Acinetobacter bouvetii
Acinetobacter calcoaceticus
Acinetobacter gerneri
Acinetobacter grimontii
Acinetobacter haemolyticus
Acinetobacter johnsonii
Acinetobar junii
Acinetobacter lwoffii
Acinetobacter parvus
Acinetobacter radioresistens
Acinetobacter schindleri
Acinetobacter tandoii
Acinetobacter tjernbergiae
Acinetobacter towneri
Acinetobacter ursingii

Acinetobacter is a Gram-negative genus of Bacteria belonging to the Gammaproteobacteria. Non-motile, Acinetobacter species are oxidase-negative, and occur in pairs under magnification. They are important soil organisms where they contribute to the mineralisation of, for example, aromatic compounds. Acinetobacter are a key source of infection in debilitated patients in the hospital.[1]

Contents

Etymology

Acinetobacter is a compound word from scientific Greek which literally means 'nonmotile rod'. The first element acineto- is an unusual transliteration of the Greek ακινητο-; the usual romanization in English is akineto-, as in akinetic.

Identification

Using FLN, or Fluorescence-Lactose-Denitrification medium, to find the amount of acid produced by metabolism of glucose, different species of bacteria under this genus can be identified.

Description

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Microbiology

Species of the genus Acinetobacter are strictly aerobic nonfermentative gram-negative bacilli. They show preponderantly a coccobacillary morphology on nonselective agar. Rods predominate in fluid media, especially during early growth.

The morphology of Acinetobacter spp. can be quite variable in Gram stained human clinical specimens, and cannot be used to differentiate Acinetobacter from other common causes of infection.

Most strains of Acinetobacter, except some of the A. lwoffii strain, grow well on MacConkey agar (without salt). Although officially classified as non-lactose fermenting, they are often partially lactose fermenting when grown on MacConkey agar. They are oxidase negative, nonmotile and usually nitrate negative.

Taxonomy

The genus Acinetobacter comprises 17 validly named and 14 unnamed (genomic) species.[2] Some unrelated (genomic) species have common designations, while some other species seem to be congruent but have different names. The knowledge of the biology or ecology of acinetobacters at species level is limited. This is because identification of acinetobacters at species level is difficult. A phenotypic species identification system has been described and a variety of genotypic methods has been explored and applied to investigate the diversity or phylogeny in the genus. These methods include high resolution fingerprinting with AFLP, PCR-RFLP with digestion of PCR amplified sequences, and analysis of various DNA sequences. Of these, AFLP analysis and amplified 16SrRNA ribosomal DNA restriction analysis have been validated with large numbers of strains of all described species. Nucleotide sequence based methods are expected to be the standard for identification in the near future.[2]

However, because routine identification in the clinical microbiology laboratory is not (yet) possible, they are divided and grouped into three main complexes:

  • Acinetobacter calcoaceticus-baumanii complex: glucose-oxidising nonhemolytic, (A.baumannii can be identified by OXA-51 typing)
  • Acinetobacter lwoffii: glucose-negative nonhemolytic
  • Acinetobacter haemolyticus: hemolytic

Natural habitat

Acinetobacter spp are widely distributed in nature. They are able to survive on various surfaces (both moist and dry) in the hospital environment, thereby being an important source of infection in debilitated patients. Occasional strains are isolated from foodstuffs and some are able to survive on various medical equipment and even on healthy human skin.

In drinking water, Acinetobacter have been shown to aggregate bacteria who otherwise do not form aggregates.

Clinical significance

Acinetobacter species are generally considered nonpathogenic to healthy individuals. However, several species persist in hospital environments and cause severe, life-threatening infections in compromised patients.[1] The spectrum of antibiotic resistances of these organisms together with their survival capabilities make them a threat to hospitals as documented by recurring outbreaks both in highly developed countries and elsewhere. An important factor for their pathogenic potential is probably an efficient means of horizontal gene transfer even though such a mechanism has so far only been observed and analyzed in Acinetobacter baylyi, a species that lives in the soil and has never been associated with infections.[1]

Most infections occur in immunocompromised individuals, and the strain A. baumannii is the second most commonly isolated nonfermenting bacteria in human specimens.

Acinetobacter is frequently isolated in nosocomial infections and is especially prevalent in intensive care units, where both sporadic cases as well as epidemic and endemic occurrence is common. A. baumannii is a frequent cause of nosocomial pneumonia, especially of late-onset ventilator associated pneumonia. It can cause various other infections including skin and wound infections, bacteremia, and meningitis, but A. lwoffi is mostly responsible for the latter. A. baumannii can survive on the human skin or dry surfaces for weeks.

Since the start of the Iraq War, over 700 U.S. soldiers have been infected or colonized by A. baumannii. Four civilians undergoing treatment for serious illnesses at Walter Reed Army Medical Center in Washington, D.C., contracted A. baumannii infections and died. At Landstuhl Regional Medical Center, a U.S. military hospital in Germany, another civilian under treatment, a 63-year-old German woman, contracted the same strain of A. baumannii infecting troops in the facility and also died. These infections appear to have been hospital acquired. [1] Based on genotyping of A. baumannii cultured from patients prior to the start of the Iraq War it is likely the soldiers contracted the infections while hospitalized for treatment in Europe.

Treatment

Acinetobacter species are innately resistant to many classes of antibiotics, including penicillin, chloramphenicol, and often aminoglycosides. Resistance to fluoroquinolones has been reported during therapy and this has also resulted in increased resistance to other drug classes mediated through active drug efflux. A dramatic increase in antibiotic resistance in Acinetobacter strains has been reported by the CDC and the carbapenems are recognised as the gold-standard and treatment of last resort.[3] Acinetobacter species are unusual in that they are sensitive to sulbactam; sulbactam is most commonly used to inhibit bacterial beta-lactamase, but this is an example of the antibacterial property of sulbactam itself.[4]

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.[5] 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 dry 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.

Identification

Schreckenberger PC, Daneshvar MI, Weyant RS, Hollis DG (2003). "Acinetobacter, Achromobacter, Chryseobacterium, Moraxella, and Other Nonfermentative Gram-Negative Rods". in Murray, Patrick R.; Baron, Ellen Jo; Jorgensen, James A.; Michael A. Pfaller; Robert H. Yolken. Manual of Clinical Microbiology (8th ed.). Washington DC: American Society Microbiology. pp. 749–79. ISBN 1-55581-255-4.  

Risk factors

Resistance

General, ICU

Acinetobacter

Therapy

Colistin

Montero A, Ariza J, Corbella X, et al. (June 2002). "Efficacy of colistin versus beta-lactams, aminoglycosides, and rifampin as monotherapy in a mouse model of pneumonia caused by multiresistant Acinetobacter baumannii". Antimicrob. Agents Chemother. 46 (6): 1946–52. doi:10.1128/AAC.46.6.1946-1952.2002. PMID 12019113. PMC 127272. http://aac.asm.org/cgi/pmidlookup?view=long&pmid=12019113.  

Reports suggest that this bacteria is susceptible to phage therapy.[6] A phage directed against Acinetobacter showed a remarkable lytic activity both in vitro and in vivo: as few as 100 pfu of phage protected mice against Acinetobacter.[7]

Biotechnology

Many of the characteristics of Acinetobacter ecology, taxonomy, physiology and genetics point to the possibility of exploiting its unique features for future applications. Acinetobacter strains are often ubiquitous, exhibit metabolic versatility, are robust and some provide convenient systems for modern molecular genetic manipulation and subsequent product engineering. These characteristics are being exploited in various biotechnological applications including biodegradation and bioremediation, novel lipid and peptide production, enzyme engineering, biosurfactant and biopolymer production and engineering of novel derivatives of these products. It is anticipated that progress in these fields will broaden the range of applications of Acinetobacter for modern biotechnology.[8]

References

  1. ^ a b c Gerischer U (editor). (2008). Acinetobacter Molecular Biology (1st ed.). Caister Academic Press. ISBN 978-1-904455-20-2. http://www.horizonpress.com/acineto.  
  2. ^ a b Dijkshoorn L (2008). "The Diversity of the Genus Acinetobacter". Acinetobacter Molecular Biology (Gerischer U, ed.). Caister Academic Press. ISBN 978-1-904455-20-2. http://www.horizonpress.com/acineto.  
  3. ^ Rahal J (2006). "Novel antibiotic combinations against infections with almost completely resistant Pseudomonas aeruginosa and Acinetobacter species". Clin Infect Dis 43 Suppl 2: S95–9. doi:10.1086/504486. PMID 16894522.  
  4. ^ Wood GC, Hanes SD, Croce MA, Fabian TC, Bougher BA. (2002). "Comparison of ampicillin-sulbactam and imipenem-cilastin for the treatment of Acinetobacter ventilator-associated pneumonia". Clin Infect Dis 34: 1425–30. doi:10.1086/340055.  
  5. ^ Centers for Disease Control and Prevention (CDC) (2004). "Acinetobacter baumannii infections among patients at military medical facilities treating injured U.S. service members, 2002-2004". MMWR Morb Mortal Wkly Rep 53 (45): 1063–6. PMID 15549020.  
  6. ^ Matsuzaki S, Rashel M, Uchiyama J, et al. (October 2005). "Bacteriophage therapy: a revitalized therapy against bacterial infectious diseases". J. Infect. Chemother. 11 (5): 211–9. doi:10.1007/s10156-005-0408-9. PMID 16258815.  
  7. ^ Brussow H (2007). "Phage Therapy: The Western Perspective". Bacteriophage: Genetics and Molecular Biology (Mc Grath S and van Sinderen D, ed.). Caister Academic Press. ISBN 978-1-904455-14-1. http://www.horizonpress.com/phage.  
  8. ^ Gutnick D (2008). "Potential Application of Acinetobacter in Biotechnology". Acinetobacter Molecular Biology (Gerischer U, ed.). Caister Academic Press. ISBN 978-1-904455-20-2. http://www.horizonpress.com/acineto.  

External links


Wiktionary

Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary

See also acinetobacter

Translingual

Proper noun

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Wikipedia

Acinetobacter

  1. a taxonomic genus, within family Moraxellaceae - Gram-negative bacteria found in soil
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Wikispecies

Up to date as of January 23, 2010

From Wikispecies

Taxonavigation

Main Page
Superregnum: Bacteria
Regnum: Bacteria
Phylum: Proteobacteria
Classis: Gamma Proteobacteria
Ordo: Pseudomonadales
Familia: Moraxellaceae
Genus: Acinetobacter
Species: Acinetobacter baumannii - Acinetobacter sp. ADP1 -

References


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