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PubMed2000

Lipase activity of Acinetobacter baumannii after treatment with meropenem.

The effects of meropenem (CAS 96036-03-2) at subinhibitory concentrations (sub-MICs; 1/4, 1/8 or 1/16 of the minimal inhibitory concentrations) on the lipase activity of 15 strains of Acinetobacter baumannii were evaluated in vitro. The lipolytic activity was demonstrated by hydrolysis of the substrate Tween 20. Meropenem at the concentrations tested affected the production of bacterial lipase. The degree of induced changes was strain and antibiotic concentration dependent. Eight strains showed an increased lipolytic activity after treatment with meropenem at all three sub-MICs tested; four strains after exposure to two concentrations, and two strains after the treatment with meropenem at one of the concentrations tested. Meropenem at all concentrations reduced the lipase activity only in one strain. In six strains the enzyme activity was decreased only after treatment with some antibiotic concentrations. The possible relevance of increased lipolytic activity in most A. baumannii strains after the effect with meropenem at subinhibitory concentrations has to be clarified by additional studies.

Acinetobacter↗
PubMed2002

Integration of foreign DNA during natural transformation of Acinetobacter sp. by homology-facilitated illegitimate recombination.

The active uptake of extracellular DNA and its genomic integration is termed natural transformation and constitutes a major horizontal gene-transfer mechanism in prokaryotes. Chromosomal DNA transferred within a species can be integrated effectively by homologous recombination, whereas foreign DNA with low or no sequence homology would rely on illegitimate recombination events, which are rare. By using the nptII(+) gene (kanamycin resistance) as selectable marker, we found that the integration of foreign DNA into the genome of the Gram-negative Acinetobacter sp. BD413 during transformation indeed was at least 10(9)-fold lower than that of homologous DNA. However, integration of foreign DNA increased at least 10(5)-fold when it was linked on one side to a piece of DNA homologous to the recipient genome. Analysis of foreign DNA integration sites revealed short stretches of sequence identity (3-8 bp) between donor and recipient DNA, indicating illegitimate recombination events. These findings suggest that homologous DNA served as a recombinational anchor facilitating illegitimate recombination acting on the same molecule. Homologous stretches down to 183 nucleotides served as anchors. Transformation with heteroduplex DNA having different nucleotide sequence tags in the strands indicated that strands entered the cytoplasm 3' to 5' and that strands with either polarity were integrated by homologous recombination. The process led to the genomic integration of thousands of foreign nucleotides and often was accompanied by deletion of a roughly corresponding length of recipient DNA. Homology-facilitated illegitimate recombination would explain the introgression of DNA in prokaryotic genomes without the help of mobile genetic elements.

Acinetobacter↗
PubMed1998

Characterization of a novel branched tetrasaccharide of 3-deoxy-D-manno-oct-2-ulopyranosonic acid. The structure of the carbohydrate backbone of the lipopolysaccharide from Acinetobacter baumannii strain nctc 10303 (atcc 17904).

For the first time, the tetrasaccharide Kdoalpha2-->5Kdoalpha2-->5(Kdoalpha2-->4)Kdo (Kdo is 3-deoxy-D-manno-oct-2-ulopyranosonic acid) has been identified in a bacterial lipopolysaccharide (LPS), i.e. in the core region of LPS from Acinetobacter baumannii NCTC 10303. The LPS was analyzed using compositional analysis, mass spectrometry, and NMR spectroscopy. The disaccharide D-GlcpNbeta1-->6D-GlcpN, phosphorylated at O-1 and O-4', was identified as the carbohydrate backbone of the lipid A. The Kdo tetrasaccharide is attached to O-6' of this disaccharide and is further substituted by short L-rhamnoglycans of varying length and by the disaccharide D-GlcpNAcalpha1-->4D-GlcpNA (GlcpNA, 2-amino-2-deoxy-glucopyranosuronic acid). The core region is not substituted by phosphate residues and represents a novel core type of bacterial LPS. The complete carbohydrate backbone of the LPS is shown in Structure I as follows: where Rha is rhamnose. Except were indicated, monosaccharides possess the D-configuration. Sugars marked with an asterisk are present in non-stoichiometric amounts.

Acinetobacter calcoaceticus↗
PubMed2002

A novel bifunctional wax ester synthase/acyl-CoA:diacylglycerol acyltransferase mediates wax ester and triacylglycerol biosynthesis in Acinetobacter calcoaceticus ADP1.

Triacylglycerols (TAGs) and wax esters are neutral lipids with considerable importance for dietetic, technical, cosmetic, and pharmaceutical applications. Acinetobacter calcoaceticus ADP1 accumulates wax esters and TAGs as intracellular storage lipids. We describe here the identification of a bifunctional enzyme from this bacterium exhibiting acyl-CoA:fatty alcohol acyltransferase (wax ester synthase, WS) as well as acyl-CoA:diacylglycerol acyltransferase (DGAT) activity. Experiments with a knock-out mutant demonstrated the key role of the bifunctional WS/DGAT for biosynthesis of both storage lipids in A. calcoaceticus. This novel type of long-chain acyl-CoA acyltransferase is not related to known acyltransferases including the WS from jojoba (Simmondsia chinensis), the DGAT1 or DGAT2 families present in yeast, plants, and animals, and the phospholipid:diacylglycerol acyltransferase catalyzing TAG formation in yeast and plants. A large number of WS/DGAT-related proteins were identified in Mycobacterium and Arabidopsis thaliana indicating an important function of these proteins. WS and DGAT activity was demonstrated for the translational product of one WS/DGAT homologous gene from M. smegmatis mc(2)155. The potential of WS/DGAT to establish novel processes for biotechnological production of jojoba-like wax esters was demonstrated by heterologous expression in recombinant Pseudomonas citronellolis. The potential of WS/DGAT as a selective therapeutic target of mycobacterial infections is discussed.

Acinetobacter↗
PubMed2006

Kinetic mechanisms of the oxygenase from a two-component enzyme, p-hydroxyphenylacetate 3-hydroxylase from Acinetobacter baumannii.

p-Hydroxyphenylacetate hydroxylase (HPAH) from Acinetobacter baumannii catalyzes the hydroxylation of p-hydroxyphenylacetate (HPA) to form 3,4-dihydroxyphenylacetate (DHPA). The enzyme system is composed of two proteins: an FMN reductase (C1) and an oxygenase that uses FMNH- (C2). We report detailed transient kinetics studies at 4 degrees C of the reaction mechanism of C2.C2 binds rapidly and tightly to reduced FMN (Kd, 1.2 +/- 0.2 microm), but less tightly to oxidized FMN (Kd, 250 +/- 50 microm). The complex of C -FMNH-2 reacted with oxygen to form C(4a)-hydroperoxy-FMN at 1.1 +/- 0.1 x 10(6) m(-1) s(-1), whereas the C -FMNH-2 -HPA complex reacted with oxygen to form C(4a)-hydroperoxy-FMN-HPA more slowly (k = 4.8 +/- 0.2 x 10(4) m(-1) s(-1)). The kinetic mechanism of C2 was shown to be a preferential random order type, in which HPA or oxygen can initially bind to the C -FMNH-2 complex, but the preferred path was oxygen reacting with C -FMNH-2 to form the C(4a)-hydroperoxy-FMN intermediate prior to HPA binding. Hydroxylation occurs from the ternary complex with a rate constant of 20 s(-1) to form the C2-C(4a)-hydroxy-FMN-DHPA complex. At high HPA concentrations (>0.5 mm), HPA formed a dead end complex with the C2-C(4a)-hydroxy-FMN intermediate (similar to single component flavoprotein hydroxylases), thus inhibiting the bound flavin from returning to the oxidized form. When FADH- was used, C(4a)-hydroperoxy-FAD, C(4a)-hydroxy-FAD, and product were formed at rates similar to those with FMNH-. Thus, C2 has the unusual ability to use both common flavin cofactors in catalysis.

Acinetobacter baumannii↗
PubMed2003

Cloning of Acinetobacter calcoaceticus chromosomal region involved in catechin degradation.

Acinetobacter calcoaceticus utilizes catechin as sole carbon source. The chromosomal region involved in catechin catabolism was cloned in Escherichia coli DH5alpha from the genomic DNA of A. calcoaceticus. A recombinant E. coli containing 9.2 kb DNA fragment of A. calcoaceticus inserted in pUC19 showed a halo zone around the colony in plate assays, indicating the catechin utilizing ability of the clone. Enzyme assays revealed the expression of the cloned DNA fragment of A. calcoaceticus. High performance thin layer chromatography confirmed protocatechuic acid and phloroglucinol carboxylic acid as cleavage products of catechin in A. calcoaceticus and the catechin degrading ability of the clones. A. calcoaceticus followed the beta-ketoadipate pathway for catechin degradation. The sub-clone (pASCI) of this insert was sequenced and analyzed. The sequence showed three major ORFs but only ORF 2 showed similarities to other aromatic oxygenases and the sequence of ORF 2 was submitted to GenBank (AF369935).

Acinetobacter calcoaceticus↗
PubMed1992

Plasmid profiles of Acinetobacter and Enterobacter species of hospital origin: restriction endonuclease analysis of plasmid DNA and transformation of Escherichia coli by R plasmids.

A total of 37 multi-resistant strains (20 Acinetobacter calcoaceticus and 17 Enterobacter cloacae) were isolated from patients of the Intensive Care Units. All the isolates were examined for resistance to a battery of antimicrobial agents by the disk diffusion method. Plasmid profiles and restriction endonuclease analysis of plasmid DNA by EcoR1 revealed the spread of one A. calcoaceticus and two E. cloacae endemic strains. Transformation experiments on Escherichia coli competent cells by three plasmids established the presence of R plasmids in the multi-resistant isolates.

Acinetobacter↗
PubMed1992

In vitro interactions of aminoglycosides with imipenem or ciprofloxacin against aminoglycoside resistant Acinetobacter baumannii.

The in vitro interactions between gentamicin, tobramycin, netilmicin and amikacin with imipenem and ciprofloxacin were evaluated by the killing curve technique against 20 clinical isolates of Acinetobacter baumannii highly resistant to aminoglycosides which were susceptible or moderately susceptible to imipenem and resistant or moderately susceptible to ciprofloxacin. Imipenem enhanced killing by gentamicin, tobramycin, netilmicin and amikacin in tests with 9, 12, 10 and 15 strains (45-75%) while ciprofloxacin with 3, 7, 5 and 6 strains (15-35%) respectively. Interaction results were influenced by the height of aminoglycoside minimum bactericidal concentrations (MBCs) but were independent of imipenem or ciprofloxacin MBCs and the presence of aminoglycoside modifying enzymes. It is concluded that enhanced killing after aminoglycoside interaction with imipenem or ciprofloxacin versus A. baumannii cannot be predicted but it should be carefully tested in vitro. The in vivo significance of the reported findings mandates clinical studies in humans.

Acinetobacter↗
PubMed1999

Biochemical properties of the protein tyrosine kinase of the bacterium Acinetobacter johnsonii.

The biochemical properties of the autophosphorylating protein tyrosine kinase of Acinetobacter johnsonii were analyzed in vitro. The study shows that the optimal pH value for the phosphorylation reaction is approximately 7. The enzyme activity is stimulated by magnesium and, to a lesser extent, by manganese ions, whereas calcium ions have no effect. The phosphorylation process is rapid reaching a maximum in < 2 min, and the enzyme is modified at multiple sites. Interestingly, the bacterial enzyme is insensitive to a series of molecules known to affect the activity of eukaryotic protein tyrosine kinases: genistein, quercetin, tosyllysine chloromethyl ketone, and vanadate. We concluded that, even though the overall phosphorylation reaction catalyzed by the A. johnsonii enzyme is identical to that occurring in eukaryotes, this bacterial kinase exhibits a number of specific properties and therefore probably belongs to a separate group in the general family of protein tyrosine kinases.

Acinetobacter↗
PubMed2002

The cost of antibiotic resistance: effect of resistance among Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, and Pseudmonas aeruginosa on length of hospital stay.

To assess the effect of antimicrobial resistance on length of hospital stay, a case-control study compared infections due to four nosocomial pathogens. Significantly increased lengths of stay were associated with infections due to methicillin-resistant Staphylococcus aureus, extended-spectrum beta-lactamase-producing Klebsiella pneumoniae, and carbapenem-resistant Acinetobacter baumannii or Pseudomonas aeruginosa. Infections with resistant pathogens are associated with prolonged hospitalization.

Acinetobacter↗
PubMed2002

Completely resistant Acinetobacter baumannii strains.

Nosocomially acquired completely resistant Acinetobacter baumannii strains are a major clinical concern. We identified completely resistant A. baumannii in 6 (4.9%) of 122 A. baumannii isolates in a retrospective chart review at two teaching hospitals. All of these patients had received broad-spectrum antibiotics and had severe underlying comorbid illnesses, long hospitalizations, or recent surgical procedures; 3 had been in the intensive care unit. Five (83%) of the 6 patients were older than 70 years. Only one death occurred. Strict infection control measures may limit further spread.

Acinetobacter Infections↗
PubMed2006

Mechanisms of multidrug resistance in Acinetobacter species and Pseudomonas aeruginosa.

Acinetobacter species and Pseudomonas aeruginosa are noted for their intrinsic resistance to antibiotics and for their ability to acquire genes encoding resistance determinants. Foremost among the mechanisms of resistance in both of these pathogens is the production of beta -lactamases and aminoglycoside-modifying enzymes. Additionally, diminished expression of outer membrane proteins, mutations in topoisomerases, and up-regulation of efflux pumps play an important part in antibiotic resistance. Unfortunately, the accumulation of multiple mechanisms of resistance leads to the development of multiply resistant or even "panresistant" strains.

Acinetobacter↗
PubMed2006

Emergence of carbapenem resistance in Acinetobacter baumannii recovered from blood cultures in Australia.

We describe the first emergence of carbapenem-resistant Acinetobacter baumannii in Australia. Ninety A. baumannii isolates recovered from cultures of blood specimens from 69 patients were analyzed. Overall, 58 isolates (64%) were resistant to meropenem. The chi 2 test for linear trend revealed that emergence of carbapenem resistance was statistically significant during the 32-month study period. Selected isolates were of the same clonal type, and no genes encoding carbapenemases were identified.

Acinetobacter baumannii↗
PubMed1999

Intravenous colistin as therapy for nosocomial infections caused by multidrug-resistant Pseudomonas aeruginosa and Acinetobacter baumannii.

Sixty nosocomial infections caused by Pseudomonas aeruginosa and Acinetobacter baumannii resistant to aminoglycosides, cephalosporins, quinolones, penicillins, monobactams, and imipenem were treated with colistin (one patient had two infections that are included as two different cases). The infections were pneumonia (33% of patients), urinary tract infection (20%), primary bloodstream infection (15%), central nervous system infection (8%), peritonitis (7%), catheter-related infection (7%), and otitis media (2%). A good outcome occurred for 35 patients (58%), and three patients died within the first 48 hours of treatment. The poorest results were observed in cases of pneumonia: only five (25%) of 20 had a good outcome. A good outcome occurred for four of five patients with central nervous system infections, although no intrathecal treatment was given. The main adverse effect of treatment was renal failure; 27% of patients with initially normal renal function had renal failure, and renal function worsened in 58% of patients with abnormal baseline creatinine levels. Colistin may be a good therapeutic option for the treatment of severe infections caused by multidrug-resistant P. aeruginosa and A. baumannii.

Acinetobacter Infections↗
PubMed1990

Plasmid DNA fingerprinting of Acinetobacter calcoaceticus subspecies anitratus from intubated and mechanically ventilated patients.

Forty-three intubated and mechanically ventilated patients in five intensive care units (ICUs) of one hospital developed respiratory colonization or infection with Acinetobacter calcoaceticus subspecies anitratus over a 16-month interval. Neither the frequency nor rate of A anitratus isolation exceeded the hospital endemic norms. Single isolates from 34 of the patients were subtyped by plasmid DNA analysis, two biotyping systems and antimicrobial susceptibility to 24 drugs. Plasmid DNA fingerprints were distinct in 18 isolates (they differed from each other and all others), similar in two and identical or similar in ten. The latter group of isolates were recovered from patients in four ICUs. Reproducibility of biotyping was poor. Neither biotyping nor antimicrobial susceptibility were successful in identifying sameness among the group isolates nor differences among other isolates. We conclude that plasmid DNA fingerprinting should be used to assess the possibility of multiple patient transmissions of the same A anitratus strain in the absence of an obvious outbreak.

Acinetobacter↗
PubMed1996

Mortality due to ventilator-associated pneumonia or colonization with Pseudomonas or Acinetobacter species: assessment by quantitative culture of samples obtained by a protected specimen brush.

Ventilator-associated pneumonia (VAP) due to multiresistant pathogens is associated with a high death rate. We analyzed the relationship between VAP due to Pseudomonas or Acinetobacter species and death by comparing the outcomes for patients colonized with these pathogens (bacterial counts of < 10(3) cfu/mL) with those for patients with pneumonia due to these pathogens (bacterial counts of > or = 10(3) cfu/mL). Samples were obtained systematically with a protected specimen brush when pneumonia was suspected. Clinical characteristics at admission to our intensive care unit and clinical features at the time of suspicion of VAP were not significantly different between colonized patients and those with VAP. Mortality rates were 29% among colonized patients and 73% among patients with VAP (P < .001). These results demonstrate a relationship between a high mortality rate and the development of pneumonia due to multiresistant, nonfermenting, gram-negative bacilli ( > or = 10(3) cfu/mL) in the lower airways of patients receiving ventilatory support.

Acinetobacter↗
PubMed1996

Investigation of a multiyear multiple critical care unit outbreak due to relatively drug-sensitive Acinetobacter baumannii: risk factors and attributable mortality.

From 1990 to 1993, an outbreak of respiratory Acinetobacter baumannii infection occurred in five intensive care units (ICUs) of a tertiary care center. A. baumannii was subsequently isolated from disinfected temperature probes and ventilator circuits. Pulsed-field gel electrophoresis suggested that a single strain accounted for 93% of patient isolates and 88% of environmental isolates. Univariate risk factors for A. baumannii acquisition were tracheostomy (P < .01), ventilation >3 days (P < .01), dialysis (P = .03), Stenotrophomonas maltophilia respiratory colonization (P = .02), parenteral nutrition (P = .05), and enteric feeding (P < .01). Logistic regression analysis showed duration of ventilation and enteric feeding to be independent risk factors. The outbreak strain was relatively antibiotic-susceptible, but the mortality attributable to respiratory A. baumannii acquisition was 23%. Only the APACHE II score was independently associated with increased mortality. Multifaceted control measures, including gas sterilization of temperature probes, terminated the outbreak.

Acinetobacter Infections↗