Taxonomy And Historical Features Of Of Acinetobacter Biology Essay

Among the last decennaries, bacteriums of the genus “ Acinetobacter ” have designed of import nosocomial pathogens, particularly in ICU units. Acinetobacter spp are widespread nowadays in H2O and dirt as nonparasitic saprophytic organisms ( Greenwood et al. , 2001 ) .Acinetobacters were foremost described under the group of “ Micrococcus calcoaceticus ” by Beijerinck in 1911.

In 1956 these bacteriums were so classified under the name of “ Moraxella ” in France. In this period a group of France workers had detected a genus named Acinetobacter. In 1968 a phenotypic survey of 106 strains was done by Baumann resulted in the acknowledgment of merely a individual genus named Acinetobacter bummanii ( Towner, 1997 ) . In early 1970 ‘s, Acinetobacters were normally sensitive to many common antimicrobic agents ( Greenwood et al. , 2001 ) . However in the same period many microbiologists in infirmaries discovered that these beings were infective and involved in assorted nosocomial infections. In 1986, a basic subdivision of the genus Acinetobacter was done by Bovetand and Grimont who identified 12 genomic species by DNA- DNA hybridisation method.

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However, today there are at least 19 genomic species of Acinetobacter ( Murray et al. , 2007 ) .Within the genus, Acinetobacter baumannii appears to be the species of greatest clinical importance, but other species of the ‘A. baumannii composite ‘ ( consisting A. baumannii, Acinetobacter calcoaceticus, and the nameless sp. 3 and sp.

13 of Tjernberg and Ursing ) are besides of clinical importance. The A. baumannii complex contains isolates that are multi-resistant to antibiotics and that have been responsible for many eruptions of infection throughout the universe ( Towner, 1997 ) . The A. baumannii composite should be considered to be as different from other Acinetobacterspp. as S. aureus is from coagulase negative staphylococcus.

Other Acinetobacter spp. are involved merely seldom in human disease and eruptions of infection, and are by and large isolatedfrom patients who are already enduring from terrible underlying disease ( Joly-Guillou, 2005 ) .

Laboratory Diagnosis:

Morphologically, they are aerophilic, non motile Gram-negative coccobacilli and normally found in diploid formation or ironss of variable length. They are purely aerophilic and grow easy on all common media at temperatures from 20 to 30 oC, with for most strains, the optimum at 33-35 oC. They are oxidase-negative, catalase-positive, indole-negative and nitrate-negative. It does non hold capsule as it is non produce cytochrome oxidase. Furthermore, the initial hint of these bacteriums is the observation of bantam ( 1.

0x 0.7 Aµm ) diplococci on gm discoloration ( Koneman et al. , 1997 ) .Colonies appear smooth, opaque, and somewhat smaller than those of members of the household Enterobacteriaceae on blood agar. Most strains appear colourless, somewhat pink or lavender in coloring material on MacConkey agar due to lactose oxidization ( Engelkirk, 2007 ) .

Therefore, the genus of Acinetobacter can be subdivided into two groups. Acinetobacter that is able to oxidize glucose are called saccharolytic, with those that are unable called asaccharolytic ( Engelkirk, 2007 ) .However, most glucose-oxidizing non-haemolytic clinical strains are A. baumannii, most glucose-negative non-haemolytic 1s are A. lwoffii, and most hemolytic 1s are A. hemolytic ( Murray et al.

, 2007 ) .

Clinical characteristics of Acinetobacter infections:

Acinetobacter spp. , peculiarly Acinetobacter baumannii, can do many clinical upsets, including pneumonia, secondary meningitis, bacteraemia, wound infections in burn patients and urinary piece of land infections ( Winn et al. , 2005 ) . It is besides isolated from tegument, pharynx and many secernments of normal people as commonsal vegetations ( Hawkey & A ; Bergogne-Berezin, 2006 ) .In instance of lesion infections it frequently leads to bacteraemia within 3-5 yearss following infection. In several big instance series, 4-27 % of all Acinetobacter bacteraemia occurred as a consequence of septic surgical or fire lesions ( Gillespie, 2004 ; Hawkey & A ; Bergogne-Berezin, 2006 ) .

Such infections are frequently hard to handle because of the ability of Acinetobacters to go rabidly opposition to multiple antibiotics, including aminoglycosides, expanded-spectrum Mefoxins, carbapenems and fluoroquinolones ( Towner and Gallego, 2001 ) . Furthermore, Acinetobacters which can easy obtain from dirt, H2O, nutrient and sewerage ( Towner, 1997 ) are able to last for long periods in inanimate environments ( Greenwood et al. , 2001 ) .Inappropriate or inordinate usage of antibiotics therapy ( i.e 3rd coevals Mefoxin ) , surgery, usage of medical machinery ( i.e ventilators ) , interpolation of catheters intravenously or urinary, and prolonged infirmary stay are all identified as hazard factors for colonization/infection with Acinetobacter ( Hawkey & A ; Bergogne-Berezin, 2006 ) .

Acinetobacter has been isolated in a big assortment of clinical samples, including blood, piss, fecal matters, cerebrospinal fluid and phlegm ( Gillespie, 2004 ) . It is timeserving pathogens and is normally found in patient samples. However, the badness of Acinetobacter infection depends upon the site of infection and the patient ‘s susceptibleness to infection as a consequence of implicit in disease ( Murray et al. , 2007 ) .

Chiang, et al. , ( 2008 ) was added in their survey increased serum creatinine degree and malignance as a hazard factors associate with increased mortality in patient with bacteraemia caused by Acinetobacter.A European study of causative agents in nosocomial pneumonia carried out in seven states utilizing the same protocol has established an over all incidence of about 10 % for Acinetobacter ( Bergogne-Berezin, 2001 ) .A survey period from 2003 to 2006 for over 270 patients admitted every twelvemonth in burn clinic confirmed the increased tendency of Acinetobacter discolorations, as multi-drug immune possible pathogen ( Babik et al. , 2008 ) .

Pathogenesis of Acinetobacter infection:

As Acinetobacter spp. are considered to be comparatively low-grade pathogens, it has legion virulency factors that have been identified ; these include:

The production of exopolysaccharide:

It is thought that the presence of exopolysaccharide capsule helps in the protection of bacteriums from host defense mechanisms, ensuing in deadliness for mice and cytotoxicity for phagocytic cells.

Approximately 30 % of Acinetobacter strains produce exopolysaccharide. This procedure hasbeen studied in Acinetobacter spp. strain BD4, which synthesises a thick exopolysaccharide capsule composed of L-rhamnose, D-glucose, D-glucuronic acid, and D-mannose, which likely renders the surface of strains more hydrophilic ( Joly-Guillou, 2005 ; Hawkey & A ; Bergogne-Berezin, 2006 ) . In experimental surveies, exopolysaccharide-producing strains of Acinetobacter have been shown to be more infective than non-exopolysaccharide-producing strains, particularly in polymicrobial infections with other species of higher virulency ( Joly-Guillou, 2005 )


Quorum-sensing is a widespread regulative mechanism among Gram-negative bacteriums suchas Pseudomonas aeruginosa. Four different quorum feeling signal molecules capable of triping N-acylhomoserine-lactone biosensors have been found in clinical isolates of Acinetobacter, with maximum activity in the stationary growing stage. Quorum-sensing might be a cardinal mechanism for auto-induction of multiple virulency factors in an timeserving pathogen such as Acinetobacter, and this procedure should be studied for its clinical deductions ( Joly-Guillou 2005 ) .

The belongings of adhesion to human epithelial cells via the capsule or fimbriae.

The production of lipase enzyme which may damage tissue lipoids.

( Bergogne-Berezin & A ; Towner, 1996 ; Hawkey & A ; Bergogne-Berezin, 2006 )

The potentially toxic function of the lipopolysaccharide constituent of the cell wall:

The lipopolysaccharide is involved in opposition to complement in human serum and Acts of the Apostless in synergism with the capsular exopolysaccharide.

Complement appears to play a function in the disinfectant activity of human sera. A relationship has been described antecedently for Gram-negative bacteriums isolated from bacteraemic patients between their grade of opposition in vitro to the lytic activity of complement and their ability to last in human fluids. Lipopolysaccharide O and capsular polyose are both involved in this phenomenon.Capsular polyose is known to barricade the entree of complement to the microbial cell wall and to forestall the triggering of the alternate tract of complement activation, as demonstrated in experimental theoretical accounts of Gram-negative infections ( Joly-Guillou, 2005 ) .Although, the outer membrane has particular channels dwelling of protein molecules called porins, that allow the inactive diffusion of low molecular weight to perforate through this membrane. Large antibiotics molecules penetrate easy, which account for the high antibiotic opposition of A.baumannii. For illustration, the permeableness of the outer membrane varies from one gm negative species to another, in Psudomonas aeruginosa, which highly opposition to antibiotics, the outer membrane is 100 times less permeable than the E.

coli ( Brooks et al. , 2001 ) . A survey showed when analyzed the permeableness of the outer membrane of acinetobacter, they found that the permeableness of Mefoxins drug was 2-7 times lower than it is found in Psudomonas aeruginosa ( Vila, 1998 ) .Many parametric quantities, including host factors, the bacterial load and the virulency of singlestrain, may play of import functions in doing infection in colonized patients. Sing thatAcinetobacter is frequently multi-resistant to antibiotics, the designation of factors act uponing virulency could assist to divide colonising strains into those of high and low possible virulency. Antibiotic therapy could be avoided for strains of low possible virulency, whereas designation of extremely deadly colonizing strains in the respiratory piece of land should take to re-inforcement of preventative cross-infection steps and early antibiotic intervention for bad patients. Careful manus rinsing with soap and H2O, and besides intoxicant based gels, should ever be encouraged ( Joly-Guillou, 2005 )

Emergence of Resistance:


baumannii and related species have acquired opposition to multiple antibiotics instead than being inherently resistant. When these species were foremost applied as human pathogens, many strains were susceptible to ampicillin and most were sensitive to the Mefoxins. In 1975, & lt ; 20 % of these strains were immune to ticarcillin. However, these bacteriums showed rapid opposition to 2nd coevals Mefoxins in the terminal 1970s and early 1980s, when these agents were being used to command nosocomial infections.

When the 3rd coevals Mefoxins were introduced, A.baumannii developed opposition to cefotoxime and ceftazidime. Therefore, this bacteria has an inordinate acquired opposition to I?-lactam drugs ( Towner, 1997 ) .

There are no specific intervention guidelines for Acinetobacter spp. due to the big fluctuation in antibiotic opposition. To find the best manner of intervention for a peculiar isolate, antimicrobic susceptibleness proving must be performed ( Forbes, 2007 ) .

Although, carbapenems were the drug of penchant in the intervention of acinetobacter infections. Numerous studies in the medical and scientific literature have documented opposition strain to carbapenems antibiotics such as imipenem and meropenem ( Costa et al. , 2000 ; Levin, 2002 )Harmonizing to Health Protection Agency ( HPA ) study 1,225 instances of bacteraemia due to Acinetobacter spp were reported from England, Wales and Northern Ireland in 2007, with an overall incidence rate of 2.2 per 100,000 populations. In the same study 12 % of Acinetobacter spp was shown opposition to imipenem.

Whereas, prevalence of Cipro and Garamycin opposition was 16 % and 12 % severally.Presently, several studies were studied the prevalence, manner of transmittal and hazard factors of multi-drug immune A. baumannii in ICU and fire clinic. It was reported an addition incidence and a spread of an eruption of epidemic ringer of A. baumannii ( Babik et al.

, 2008 ; Cootz & A ; Marra, 2008 ; Fontana et al. , 2008 ; Bacakoglu et al. , 2009 ; Barchitta et al. , 2009 ) .

Carbapenems action on Acinetobacter:

Carbapenem antibiotics have the most drawn-out spectrum of antibacterial activity among all ?-lactams and imipenem is one of the most of import agents of carbapenems.Imipenem is an active agent against many beings including Gram positive and negative aerobes and anaerobes bacteriums. It is a disinfectant agent that kills or destroys bacteriums at 2-4 times the MIC for most species ( Greenwood et al. , 2001 ) .

The initial measure of drug action in destructing bacterium is the binding of the drug to cell receptors penicillin adhering proteins ( PBPs ) . After a I?-lactam drug has attached to one or more receptors, the transpeptidation reaction is inhibited and peptidoglycan synthesis is blocked. Following measure, involves the remotion or inactivation of an inhibitor of autolytic enzymes in the cell wall. This activates the lytic enzyme which consequences in lyses of cells leads to cell decease ( Brooks et al. , 2001 ) .

Mechanisms of Carbapenems Resistance:

Some early studies described acinetobacters with ?-lactamase-independent carbapenem opposition, but most recent studies describe ?-lactamase-mediated opposition.In the last few old ages, carbapenem-resistant A.A baumannii isolates have been reported worldwide. However, most carbapenem-resistant Acinetobacters have OXA-type ?-lactamases with a weak activity against carbapenems which belong to category D ?-lactamase ; such enzymes have been found in A. baumannii isolates from Argentina, Belgium, Kuwait, Scotland, Spain and Singapore. Several of these enzymes have been sequenced and are found to organize a subgroup among category D ?-lactamases, soon consisting the OXA-23, -24, -25, -26, -27 and -40 types ( Song et al.

, 2004 ) .Major carbapenemases found in acinetobacter species were metalloenzyme and OXA-type enzymes ( Bou et al. , 2000 ) . These enzymes can hydrolyze imipenem quickly ( Song et al.

, 2004 ) .There are several factors that determine the acquisition of multi opposition in A.A baumannii, these are:First, the intrinsic opposition of the micro-organisms, which obtained from low degree diffusion of certain antibiotics through the outer membrane due to low figure of porins present ( Levin, 2002 ) . Second, the installation of geting genetic sciences elements ; there are 3 types of nomadic familial elements have been found in Acinetobacter. These are the plasmids, the jumping genes and the integrons ( Vila, 1998 ) . The plasmids contains 3 opposition cistrons ; cistrons encoding ?-lactamase TEM-1, TEM-2, and CARB-5 ( Bou et al. , 2000 ) . The plasmid encoded B-lactamases have a great attending in which the opposition of this bacteriums occur by a individual familial event.

However, this type of opposition occurs largely in the extremely selective environment of the infirmary ( Greenwood, 2000 ) . Whereas, the integrons which are ironss of cistrons have a great mobility to reassign from one location of A.baumannii chromosome to another with aid of jumping gene that carry this cistron ( Vila, 1998 ) . Third factor is the ability of Acinetobacter spp to last in human and environmental reservoirs in which the cistrons of opposition may be transferred ( Vila, 1998 ) .

Acinetobatcer Treatment with Honey:

Due to the outgrowth of bacterial resistant to antibiotics, the bactericidal belongingss of manuka honey have been extensively researched.

Presently, few surveies were reported the antibacterial activity of honey against Acinetobacter. George & A ; Cutting, ( 2007 ) initiated an in-vitro survey of antibacterial activity of Medihoney against 130 clinical isolates of multi-drug immune beings including Acinetobacter. The survey was shown that 8 % ( v/v ) of honey concentration was required to suppress the immune Acinetobacter strains.The more resent one was carried out utilizing Malayan tualang honey against lesion pathogens including Acinetobacter and compare it with manuka honey.

The antibacterial activity for both honeys was same as the MIC scopes between ( 11.25 & A ; 12.5 % ) ( Tan et al. , 2009 ) .Although Acinetobacter have been found susceptible to the honey.

It required more nonsubjective grounds of clinical trails and in carnal theoretical accounts to find conditions honey has a similar antimicrobic consequence in-vivo.


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