Acinetobacter: Difference between revisions

{{shortShort description|Genus of bacteria}}

'''''Acinetobacter''''' is a [[genus]] of [[gramGram-negative]] bacteria belonging to the wider class of [[Gammaproteobacteria]]. ''Acinetobacter'' species are [[Oxidase test|oxidase-negative]], exhibit [[twitching motility]],<ref>{{Cite journal|last1=Bitrian|first1=Mariana|last2=González|first2=Rodrigo H.|last3=Paris|first3=Gaston|last4=Hellingwerf|first4=Klaas J.|last5=Nudel|first5=Clara B.|s2cid=42820743|date=2013-09-01|title=Blue-light-dependent inhibition of twitching motility in Acinetobacter baylyi ADP1: additive involvement of three BLUF-domain-containing proteins|journal=Microbiology |volume=159|issue=Pt 9|pages=1828–1841|doi=10.1099/mic.0.069153-0|doi-access=free |issn=1465-2080|pmid=23813679|hdl=11336/6600 |hdl-access=free}}</ref> and occur in pairs under magnification.

Species of the genus ''Acinetobacter'' are [[Aerobic organism|strictly aerobic]], [[Fermentation (biochemistry)|nonfermentative]], [[Gram-negative]] [[Bacteria#Morphology|bacilli]]. They show mostly a [[Coccobacillus|coccobacillary]] morphology on nonselective agar. Rods predominate in fluid media, especially during early growth.{{cncitation needed|date=August 2022}}

The morphology of ''Acinetobacter'' species can be quite variable in Gram-stained human clinical specimens, and cannot be used to differentiate ''Acinetobacter'' from other common causes of infection.{{cncitation needed|date=August 2022}}

Most strains of ''Acinetobacter'', except some of the ''A. lwoffii'' strain, grow well on [[MacConkey agar]] (without salt). Although officially classified as not lactose-fermenting, they are often partially lactose-fermenting when grown on MacConkey agar. They are [[oxidase]]-negative, catalase-positive, indole-negative, [[motility|nonmotile]], and usually [[nitrate]]-negative.{{cncitation needed|date=August 2022}}

Bacteria of the genus ''Acinetobacter'' are known to form intracellular inclusions of [[polyhydroxyalkanoates]] under certain environmental conditions (e.g. lack of elements such as phosphorus, nitrogen, or oxygen combined with an excessive supply of carbon sources).{{cncitation needed|date=December 2022}}

''Acinetobacter'' is a compound word from scientific Greek [α + κίνητο + βακτηρ(ία)], meaning nonmotile rod. The first element ''acineto-'' appears as a somewhat [[baroque]] rendering of the Greek [[morpheme]] ακίνητο-, commonly [[transliteration|transliterated]] in English is ''akineto-'', but actually stems from the French ''cinetique'' and was adopted directly into English.{{cncitation needed|date=August 2022}} Nevertheless, the French word also originates from the Greek privative α + κίνησις (motion) confirming the same origin from a different path.

The genus ''Acinetobacter'' comprises 38 validly named species.<ref name=Visca2011>{{cite journal |vauthors=Visca P, Seifert H, Towner KJ |title=Acinetobacter infection--an emerging threat to human health |journal=IUBMB Life |volume=63 |issue=12 |pages=1048–54 |date=December 2011 |pmid=22006724 |doi=10.1002/iub.534 |s2cid=45593914 |doi-access=free }}</ref>

Identification of ''Acinetobacter'' species is complicated by lack of standard identification techniques. Initially, identification was based on phenotypic characteristics such as growth temperature, [[colony morphology]], growth medium, carbon sources, gelatin hydrolysis, glucose fermentation, among others. This method allowed identification of ''A. calcoaceticus–A. baumannii'' complex by the formation of smooth, rounded, mucoid colonies at 37 °C. Closely related species could not be differentiated and individual species such as ''A. baumannii'' and ''Acinetobacter'' genomic species 3 could not be positively identified phenotypically.{{cncitation needed|date=August 2022}}

Because routine identification in the clinical microbiology laboratory is not yet possible, ''Acinetobacter'' isolates are divided and grouped into three main complexes:{{cncitation needed|date=August 2022}}

''Acinetobacter'' is frequently isolated in [[nosocomial infection]]s, and is especially prevalent in [[intensive care unit]]s, where both sporadic cases and [[epidemic]] and [[Endemic (epidemiology)|endemic]] occurrences are common. ''A. baumannii'' is a frequent cause of [[Pneumonia#Hospital-acquired|hospital-acquired 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.{{cncitation needed|date=August 2022}}

Of the ''Acinetobacter'', ''A. baumannii'' is the greatest cause of human disease, having been implicated in a number of hospital-acquired infections such as bacteremia, urinary tract infections (UTIs), secondary meningitis, infective endocarditis, and wound and burn infections.<ref>{{cite journal | last1 = Dent Lemuel | first1 = L | last2 = Marshall | first2 = DR | last3 = Pratap | first3 = S | last4 = Hulette | first4 = RB | year = 2010 | title = Multidrug resistant Acinetobacter baumannii: a descriptive study in a city hospital | journal = BMC Infect Dis | volume = 10 | page = 196 | doi=10.1186/1471-2334-10-196| pmid = 20609238 | pmc = 2909240 | doi-access = free }}</ref> In particular, ''A. baumannii'' is frequently isolated as the cause of hospital-acquired pneumonia among patients admitted to the [[intensive care unit]]. Risk factors include long-term intubation and tracheal or lung aspiration. In most cases of ventilator-associated pneumonia, the equipment used for artificial ventilation such as endotracheal tubes or bronchoscopes serve as the source of infection and result in the colonization of the lower respiratory tract by ''A. baumannii''. In some cases, the bacteria can go on to enter the bloodstream, resulting in bacteremia with mortality rates ranging from 32% to 52%. UTIs caused by ''A. baumannii'' appear to be associated with continuous catheterization, as well as antibiotic therapy. ''A. baumannii'' has also been reported to infect skin and soft tissue in traumatic injuries and postsurgical wounds. ''A. baumannii'' commonly infect burns and may result in complications owing to difficulty in treatment and eradication. Though less common, some evidence also links this bacterium to meningitis, most often following invasive surgery, and, in very rare cases, to community-acquired primary meningitis wherein the majority of the victims were children.<ref>{{cite journal | last1 = Siegman-Igra | first1 = Y | last2 = Bar-Yosef | first2 = S | last3 = Gorea | first3 = A | last4 = Avram | first4 = J | year = 1993 | title = Nosocomial Acinetobacter meningitis secondary to invasive procedures: report of 25 cases and review | journal = Clin Infect Dis | volume = 17 | issue = 5| pages = 843–849 | doi=10.1093/clinids/17.5.843| pmid = 8286623 }}</ref> Case reports also link ''A. baumannii'' to endocarditis, keratitis, peritonitis, and very rarely fatal neonatal sepsis.<ref>{{cite journal | last1 = Falagas | first1 = ME | last2 = Karveli | first2 = EA | last3 = Kelesidis | first3 = I | last4 = Kelesidis | first4 = T | year = 2007 | title = Community acquired Acinetobacter infections | journal = Eur J Clin Microbiol Infect Dis | volume = 26 | issue = 12| pages = 857–868 | doi=10.1007/s10096-007-0365-6| pmid = 17701432 | s2cid = 25898468 }}</ref>

The clinical significance of ''A. baumannii'' is partially due to its capacity to develop resistance against many available antibiotics. Reports indicate that it possesses resistance against broad-spectrum [[cephalosporin]]s, [[β-lactam antibiotic]]s, [[aminoglycosides]], and [[quinolones]]. Resistance to [[carbapenem]]s is also being increasingly reported.<ref>{{cite journal | last1 = Hu | first1 = Q | last2 = Hu | first2 = Z | last3 = Li | first3 = J | last4 = Tian | first4 = B | last5 = Xu | first5 = H | last6 = Li | first6 = J | year = 2011 | title = Detection of OXA-type carbapenemases and integrons among carbapenem-resistant Acinetobactor baumannii in a Teaching Hospital in China | journal = J Basic Microbiol | volume = 51 | issue = 5| pages = 467–472 | doi=10.1002/jobm.201000402| pmid = 21656808 | s2cid = 10955468 | doi-access = free }}</ref><ref>{{cite journal | first1 = Pierre Edouard | last1 = Fournier | last2 = Richet | first2 = H | year = 2006 | title = The epidemiology and control of Acinetobacter baumannii in healthcare facilities | doi =10.1086/500202 | pmid = 16447117 | journal = Clin Infect Dis | volume = 42 | issue = 5| pages = 692–699 | doi-access = free }}</ref> ''A. baumannii'' can survive on the human skin or dry surfaces for weeks and is resistant to a variety of disinfectants, making it particularly easy to spread in a hospital setting.<ref name=Peleg2008>{{cite journal|title=''Acinetobacter baumannii'': Emergence of a Successful Pathogen |author1=Peleg AY |author2=Seifert H |author3=Paterson DL |journal=Clinical Microbiology Reviews |date=July 2008 |volume=21 |issue=3 |pages=538–582 |pmc=2493088 |doi=10.1128/CMR.00058-07 |pmid=18625687}}</ref> Antibiotic resistance genes are often plasmid-borne, and plasmids present in ''Acinetobacter'' strains can be transferred to other pathogenic bacteria by [[horizontal gene transfer]].{{cncitation needed|date=December 2022}}

''Acinetobacter'' species are innately resistant to many classes of antibiotics, including [[penicillin]], [[chloramphenicol]], and often [[aminoglycoside]]s. Resistance to [[fluoroquinolones]] has been reported during therapy, which has also resulted in increased resistance to other drug classes mediated through active drug [[efflux (microbiology)|efflux]]. A dramatic increase in [[antibiotic resistance]] in ''Acinetobacter'' strains has been reported by the [[Centers for Disease Control and Prevention]] (CDC), and the carbapenems are recognised as the gold-standard and treatment of last resort.<ref name=Rahal_2006>{{cite journal | author = Rahal J | title = Novel antibiotic combinations against infections with almost completely resistant ''Pseudomonas aeruginosa'' and ''Acinetobacter'' species | journal = Clin Infect Dis | volume = 43 Suppl 2 | pages = S95–9 | year = 2006 | issue = Suppl 2 | pmid = 16894522 | doi = 10.1086/504486| doi-access = free }}</ref> ''Acinetobacter'' species are unusual in that they are sensitive to [[sulbactam]], which is commonly used to inhibit bacterial beta-lactamase, but this is an example of the antibacterial property of sulbactam itself.<ref name="Wood2002">{{cite journal |vauthors=Wood GC, Hanes SD, Croce MA, Fabian TC, Bougher BA | title=Comparison of ampicillin-sulbactam and imipenem-cilastatin for the treatment of ''Acinetobacter'' ventilator-associated pneumonia | journal=Clin Infect Dis | year=2002 | volume=34 | pages=1425–30 | doi=10.1086/340055 | pmid=12015687 | issue=11| doi-access=free }}</ref> Recently sulbactam-durlobactam, a new antibacterial combination undergoing phase 3 trial, has demonstrated good ''in vitro'' activity also against carbapenem-resistant ''A. baumannii'' isolates (92% susceptibility).<ref>{{Cite journal |last1=Segatore |first1=Bernardetta |last2=Piccirilli |first2=Alessandra |last3=Cherubini |first3=Sabrina |last4=Principe |first4=Luigi |last5=Alloggia |first5=Giovanni |last6=Mezzatesta |first6=Maria Lina |last7=Salmeri |first7=Mario |last8=Di Bella |first8=Stefano |last9=Migliavacca |first9=Roberta |last10=Piazza |first10=Aurora |last11=Meroni |first11=Elisa |last12=Fazii |first12=Paolo |last13=Visaggio |first13=Daniela |last14=Visca |first14=Paolo |last15=Cortazzo |first15=Venere |date=2022-08-22 |title=In Vitro Activity of Sulbactam–Durlobactam against Carbapenem-Resistant Acinetobacter baumannii Clinical Isolates: A Multicentre Report from Italy |journal=Antibiotics |language=en |volume=11 |issue=8 |pages=1136 |doi=10.3390/antibiotics11081136 |pmid=36010006 |pmc=9404735 |issn=2079-6382|doi-access=free }}</ref>