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PubMed2002

Multiple operons connected with catabolism of aromatic compounds in Acinetobacter sp. strain ADP1 are under carbon catabolite repression.

Repression of enzymes contributing to degradation of aromatic compounds via the beta-ketoadipate pathway in the presence of additional carbon sources (carbon catabolite repression) in the bacterium Acinetobacter sp. strain ADP1 is described. The phenomenon was investigated on the level of specific activity of protocatechuate 3,4-dioxygenase and p-hydroxybenzoate hydroxylase participating in catabolism of protocatechuate and p-hydroxybenzoate. Strong repression (90%) was found in cells grown on succinate and acetate in addition to the aromatic carbon source; partial derepression occurred towards the end of the logarithmic growth phase. Glucose, pyruvate, or lactate as secondary carbon sources had no repressing effect. The consumption of the aromatic substrate from the medium was delayed in the presence of acetate and succinate. The differences in specific enzyme activities were reflected at the transcript level for three operons connected to catabolism of aromatic compounds (pob, pca, van) as shown by Northern blot hybridization. Transcriptional fusions between the promoters of the pob and the pca operon identified the transcriptional level as the regulatory one. A mechanism of global regulation is postulated, which enables the organism to consume the offered carbon sources hierarchically in the most efficient manner.

Acinetobacter↗
PubMed2002

Competitive growth kinetics of Sphaerotilus natans and Acinetobacter anitratus.

Growth kinetics of Sphaerotilus natans and Acinetobacter anitratus (strain E932) in pure and mixed cultures were analysed. In order to determine mixed cultures biomass composition, a quantitative image analysis technique was developed. Pure culture studies showed that for dilution rates less than 0.188 h(-1), the filamentous micro-organism will predominate leading to bulking phenomena. By using the developed technique to determine biomass composition, mixed culture experiments showed that changes in the dilution rate modify the microbial composition of the biomass determining which micro-organism predominate. The stated equations that predict the predominance of S. natans at low dilution rates agree satisfactorily with the obtained results.

Acinetobacter↗
PubMedDate not supplied

[Intensification of the exopolysaccharide synthesis by Acinetobacter sp. on an ethanol-glucose mixture: aspects related to biochemistry and bioenergetics].

The possibility of intensifying the synthesis of microbial exopolysaccharides (EPS) by a strain of Acinetobacter sp. grown on a mixture of two substrates nonequivalent in terms of bioenergetics (ethanol + glucose) was shown. Based on theoretical calculations of the energy requirements for biomass and EPS synthesis from the energy-deficient substrate (glucose), the supplementary concentration of the energy-excessive substrate (ethanol) was determined that prevents the loss of glucose carbon that occurs when glucose is oxidized to CO2 to obtain energy for the processes of constructive metabolism. This made it possible to increase the efficiency of conversion of the substrate carbon to EPS. The introduction of ethanol into glucose-containing medium at a molar ratio of 3.1:1 allowed the amount of the EPS synthesized to be increased 1.8- to 1.9-fold; their yield relative to biomass increased 1.4- to 1.7-fold, and the yield of EPS relative to the substrate consumed increased 1.5- to 2-fold as compared to growth of the producer on single substrates. These results form the basis for the development of new technologies for obtaining secondary metabolites of practical value with the use of mixed growth substrates.

Acinetobacter↗
PubMed2003

[Effect of tobramycin on characteristics of strains of Acinetobacter species].

Suppression of bacterial growth in seven strains of the Acinetobacter species after 30 min treatment with tobramycin at suprainhibitory concentrations (postantibiotic effect--PAE) and at supra-sub-inhibitory concentrations (postantibiotic effect of subinhibitory concentrations--PA SME) as well as changes in surface hydrophobicity and in the production of lipase and histamine in the exposed strains were studied. Pharmacodynamic parameters (PAE and PA SME) as well as changes in bacterial characteristics tested were dependent on antibiotic concentration and on the strain used. Suppression of bacterial growth after treatment with tobramycin at 2 x MIC was in a range of 0.6-4.5 h, a higher concentration (4 x MIC) induced a longer PAE (1.9-5.4 h). Tobramycin at supra-subinhibitory concentrations (2 x MIC + 0.2 x MIC and 4 x MIC + 0.2 x MIC) caused total suppression of bacterial growth. In the majority of the tobramycin-treated strains, an increase in hydrophobicity manifested by adherence of bacteria to xylene as well as an increase in lipolytic activity was observed. Tobramycin at the concentrations tested did not affect the production of histamine.

Acinetobacter↗
PubMedDate not supplied

Bactericidal activity of ciprofloxacin upon Escherichia coli and Acinetobacter baumanni.

The mechanisms of bactericidal activity of ciprofloxacin (mechanisms A and B) upon cells of a strain of Escherichia coli and one strain of Acinetobacter baumannii were investigated under different conditions. The killing of E. coli cells by ciprofloxacin was significantly reduced by chloramphenicol, but this antibiotic showed almost no activity upon killing of A. baumannii cells by this quinolone. Similar results were obtained when rifampicin was added to ciprofloxacin. Bactericidal activity of ciprofloxacin upon nondividing cells of E. coli was lower and that upon non-dividing cells of A. baumannii was not affected when compared with activity of ciprofloxacin upon dividing cells of both microorganisms. These results demonstrate that the antibacterial activity of ciprofloxacin upon A. baumannii is independent of protein and ARN synthesis, a fact which suggests that this quinolone exerts only bactericidal mechanism B upon A. baumannii. This finding might explain, at least in part, the lower susceptibility of this microorganism to ciprofloxacin.

Acinetobacter↗
PubMed1990

Natural transformation in Acinetobacter calcoaceticus.

Acinetobacter calcoaceticus is a metabolically versatile microorganism that is naturally competent for DNA uptake and incorporation. We have exploited the natural state of competency for studies involving the cloning, organization and expression of genes encoding catabolic enzymes. A. calcoaceticus is able to take up, at high efficiency, genetically engineered DNA, incorporate the DNA and stably maintain and express the DNA. Sequence analysis of cloned A. calcoaceticus DNA reveals a great deal of internal repetition and secondary structure, but no specific sequences associated with uptake appear to be present. Uptake and transformation occurs in solid and liquid medium, at a wide range of DNA concentrations and with little restriction barrier to the source of the transforming DNA.

Acinetobacter↗
PubMed1991

Cloning and nucleotide sequences of the AccI restriction-modification genes in Acinetobacter calcoaceticus.

The genes of the AccI restriction-modification system specific for GT(A/C) (G/T)AC were cloned from the chromosomal DNA of Acinetobacter calcoaceticus, and their nucleotides sequenced. The restriction and modification genes coded for polypeptides with calculated molecular weights of 42,494 and 63,078, respectively. Both the enzymes were coded by the same DNA strand and the restriction gene was upstream of the methylase gene, separated by 2 bp. The restriction gene was significantly expressed in E. coli cells, so that the AccI restriction endonuclease could be purified to homogeneity. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gel filtration indicated that the catalytically active form of the endonuclease was tetrameric. Sequence comparison with related enzymes indicated that AccI methylase contained a segment of tetra-amino acids, NPPY, characteristic of N6-adenine methylases. In addition, some homologous regions were found in the sequence of HincII methylase specific for GT(C/T) (A/G)AC.

Acinetobacter↗
PubMed1991

Purification and characterization of nitrilase responsible for the enantioselective hydrolysis from Acinetobacter sp. AK 226.

A nitrilase was purified, apparently to homogeneity, from a cell extract of Acinetobacter sp. AK 226, which converts racemic 2-(4'-isobutylphenyl)propionitrile (Ibu-CN) to S-(+)-2-(4'-isobutyl-phenyl)propionic acid (S-(+)-ibuprofen). The molecular weight of the native enzyme was estimated as 580,000 upon gel filtration. The nitrilase hydrolyzed many kinds of nitrile compounds such as aliphatic, aromatic, and heterocyclic mononitriles or dinitriles. The amino-terminal amino acids were sequenced and found to be partly homologous to a nitrilase from Klebsiella pneumoniae subsp. ozanae. The purified enzyme had a pH optimum of 8.0 and a temperature optimum of 50 degrees C. The enzyme was not affected by chelating reagents, carbonyl reagents, reductants, most metal ions, or thiol reagents except silver ion, p-chloromercuribenzoate, and phenylmercuribenzoate. The reaction with racemic Ibu-CN resulted in the preferential production of S-(+)-ibuprofen, demonstrating that the nitrilase is highly enantioselective to S-(-)-Ibu-CN. In fact, the enzyme showed a 180-fold higher activity for racemic Ibu-CN than that for R-(+)-Ibu-CN.

Acinetobacter↗
PubMed1976

[Purification and various properties of NADP+-dependent alcohol dehydrogenase from Acinetobacter calcoaceticus].

The constitutive NADP+-dependent alcohol dehydrogenase from Acinetobacter calcoaceticus can be accumulated about 50 fold in 3 purification steps. The end-product shows in the analytical polyacrylamide gel electrophoresis only one active enzyme band. The molecular weight of the enzyme was determined to be 235,000 by gel chromatography on Sephadex G 200, the smallest subunit shows a molecular weight of 61 000 on SDS electrophoresis. The isoelectric point is at 5.84. The KM values determined with primary aliphatic alcohols diminish in the range of the homologous order (C2--C10) with growing chain length. The KM value for hexanal is about 20 fold less than that for 1-hexanol.

Acinetobacter↗
PubMedDate not supplied

[Central metabolism in Acinetobacter sp. grown on ethanol].

The ethanol-grown cells of the mutant Acinetobacter sp. strain 1NG, incapable of producing exopolysaccharides, were analyzed for the activity of enzymes of the tricarboxylic acid (TCA) cycle and some biosynthetic pathways. In spite of the presence of both key enzymes (isocitrate lyase and malate synthase) of the glyoxylate cycle, these cells also contained all enzymes of the TCA cycle, which presumably serves biosynthetic functions. This was evident from the high activity of isocitrate dehydrogenase and glutamate dehydrogenase and the low activity of 2-oxoglutarate dehydrogenase. Pyruvate was formed in the reaction catalyzed by oxaloacetate decarboxylase, whereas phosphoenolpyruvate (PEP) was synthesized by the two key enzymes (PEP carboxykinase and PEP synthase) of gluconeogenesis. The proportion between these enzymes was different in the exponential and the stationary growth phases. The addition of the C4-dicarboxylic acid fumarate to the ethanol-containing growth medium led to a 1.5- to 2-fold increase in the activity of enzymes of the glyoxylate cycle, as well as of fumarate hydratase, malate dehydrogenase, PEP synthase, and PEP carboxykinase (the activity of the latter enzyme increased by more than 7.5 times). The data obtained can be used to improve the biotechnology of production of the microbial exopolysaccharide ethapolan on C2-substrates.

Acinetobacter↗
PubMed2003

[Siderophores and hemolysins in iron aquisition by Acinetobacter genus].

In 60 strains of Acinetobacter genus isolated from clinical material belonging to species A. baumannii, A. haemolyticus, A. junii and A. lwoffii a hydroxamate and phenol-catechol class siderophores was identified by chemical and biological testes. A correlation between siderophores production and growth intensity, species affiliation and origin of strains was found.

Acinetobacter↗
PubMedDate not supplied

Clonal spread of Acinetobacter baumannii in a general intensive care unit.

The epidemiological characterization of multiply resistant Acinetobacter baumannii isolates from a six-bed Intensive Care Unit (ICU) is described. Investigations for A. baumannii were performed in three subsequent surveillance studies. In the first study, surveillance cultures were taken from patients, health care personnel and the environment; in the second study surveillance cultures were taken at 0, 4, and 7 days from all patients admitted consecutively to the ward; and in the third study surveillance cultures were taken from patients, health care personnel and the environment. During the first study all four hospitalized patients were found to harbour A. baumannii. Hand cultures did not grow any A. baumannii when staff entered the ward from home, but 7 positive health care workers were identified out of 25 samples taken during work, and two cultures of environmental specimens grew A. baumannii. During the second study, 4 of 86 (4.6%) patients resulted colonized with A. baumannii. In the third epidemiological study, no A. baumannii was cultured from either patients, health care personnel or the environment. All isolates recovered from various patients or sources produced conserved macrorestriction Pulsed-Field Gel Electrophoresis (PFGE) patterns and showed the same antibiotic resistance; therefore, they can be considered indistinguishable. The same antibiotic resistance and macrorestriction patterns were observed in previously isolated A. baumannii strains in the ward during May 1997, suggesting the persistence of a single A. baumannii in the ICU. The present study confirms that molecular typing is an essential tool in the epidemiology and control of nosocomial infections, showing here the persistence of a single A. baumannii clone in the ICU. The origin of this strain remains unknown but, when basic infection control measures were reinforced, emphasizing the importance of hand antisepsis and judicious use of gloves, control of A. baumannii spread in the ward was achieved.

Acinetobacter baumannii↗
PubMed2004

[Aminoglycoside resistance of Acinetobacter baumannii hospital strains in the Czech Republic].

OBJECTIVE: To investigate the nature of aminoglycoside resistance of clinically important multidrug-resistant (MDR) Acinetobacter baumannii strains from the Czech Republic. MATERIAL AND METHODS: Seventy MDR hospital strains from 1991-2001 classified into pan-European clones I (n = 41) and II (n = 21) and a group of other MDR strains (n = 8) were studied. Fifteen other strains wild-type susceptible to aminoglycosides were used as controls. Susceptibility to aminoglycosides was determined by the disk diffusion and agar dilution tests. The presence of six genes encoding different aminoglycoside-modifying enzymes (AME) and of the adeB gene encoding a component of the AdeABC efflux pump was detected using PCR. RESULTS: MDR strains showed the following pattern of resistance to aminoglycosides: kanamycin (93 %; inhibition zone diameters < or =13 mm), gentamicin (87 %; MICs > or =16 mg/l), amikacin (47 %; MICs > or =64 mg/l), tobramycin (31 %; MICs > or = 16 mg/l) and netilmicin (17 %; MICs ? 32 mg/l). Forty-six (66 %) MDR strains had netilmicin MICs of 8-16 mg/l in contrast to 0.5-1.0 mg/l found for control susceptible strains. The presence of at least one of the following AME genes was detected in 66 (94 %) MDR strains: aphA1 (n = 56), aacC1 (n = 52), aphA6 (n = 39) and aadB (n = 20). The presence of these genes and phenotypes of resistance to kanamycin, gentamicin, tobramycin and amikacin were in good agreement. The genes encoding netilmicin-modifying enzymes (aacC2, aacA4) were not detected in any strain. Fifty-six (80 %) MDR strains comprised two to four different AME genes in eight combinations. Clones I and II shared all of the genes studied (with the exception of aadB not detected in clone I). The gene adeB was found in all MDR strains and eight of 15 control susceptible strains. CONCLUSION: Clinically relevant aminoglycoside resistance of Czech A. baumannii strains is significantly associated with the genes encoding enzymatic modification of kanamycin, gentamicin, amikacin and tobramycin. These genes can spread horizontally and emerge in different combinations leading to high-level resistance to multiple aminoglycosides. The AdeABC pump is likely to play a role in the intermediate susceptibility to netilmicin but further study is needed in this regard.

Acinetobacter baumannii↗
PubMed2005

New rapid screen for the detection of imipenem-resistant Acinetobacter baumanii.

A rapid screen was developed for the detection of imipenem-resistant Acinetobacter baumanii (IRAb) following a recent outbreak in the Surgical Intensive Care Unit (SICU) of a hospital in Singapore. Antimicrobial solutions of imipenem ranging from 16 mg/L to 64 mg/L were prepared in-house. Each of the antimicrobial solutions was then incorporated singularly into MacConkey agar plates by two different methods. One of the methods involved preparing MacConkey agar plates in-house and then adding the antimicrobial solution before the agar solidified (AS method). In the second method, 1 ml of the antimicrobial solution was poured onto the surface of the agar plate (LAS method). Fifty hand-nutrient broth washes of medical staff working in the SICU, Medical Intensive Care Unit, Medical Rehabilitation Ward, and Surgical Rehabilitation Ward were inoculated onto the two types of agar media. Two strains of IRAb were isolated from the hands. The LAS plates showed faster bacterial growth of resistant pathogens by about 24 h, and their detection was easier because susceptible bacteria were inhibited by the antimicrobial. The LAS method incorporating imipenem at 32 mg/L is recommended for the rapid screening of resistant pathogens in the routine clinical laboratory.

Acinetobacter baumannii↗
PubMed2005

[Comparison of different phenotypic methods detecting extended spectrum beta-lactamases in Pseudomonas aeruginosa and Acinetobacter baumannii strains].

Pseudomonas aeruginosa and Acinetobacter baumannii which are of great concern as the frequent causative agents of nosocomial infections, frequently exhibit resistance to beta-lactam antibiotics. One of the most common causes of this resistance is the presence of extended spectrum beta-lactamases (ESBL). There is still no standardized method for the detection of ESBLs in P. aeruginosa and A.baumannii strains. The aim of this study was to compare the results of Epsilomer test (E-test), combined disk (CD) and double disk synergy (DDS) methods for the detection of ESBL in a total of 38 P. aeruginosa and 45 A.baumannii strains with ceftazidim or cefotaxime MIC > or = 1 microg/ml, isolated from different clinical samples. Cefepime was included in the group of indicator antibiotics and the distance between clavulanic acid containing disk and indicator antibiotic disks was reduced to increase the sensitivity of DDS test. Of the P. aeruginosa strains, 78.9% was detected as ESBL producers by ceftazidime/ ceftazidime-clavulanic acid and 21.1% detected by cefotaxime/cefotaxime-clavulanic acid ratio. Among this group of strains, 31.5% was positive by DDS test and 84.2% was positive by CD method. Of the A.baumannii strains, 93.3% of them was positive by ceftazidime/ceftazidime-clavulanic acid and 6.6% was positive by cefotaxime/cefotaxime-clavulanic acid ratio. DDS test detected 20% and CD method detected 53.3% of the strains positive by E-test method. The use of cefotaxime together with ceftazidime as an indicator antibiotic increased the sensitivity of detection of ESBL enzymes. Although inclusion of cefepime and reduction of the distance between disks increased the detection of ESBL by DDS method, it was still less effective than E-test. Although, 28.9% of the P. aeruginosa and 13.3% of the A. baumannii strains were susceptible to ceftazidime by in vitro tests, they were ESBL producers. In conclusion, E-test method was found to be the most sensitive phenotypic method for the detection of ESBL in our study collection.

Acinetobacter baumannii↗
PubMedDate not supplied

[Regulation of C2-metabolism under mixotrofic growth conditions of Acinetobacter sp. B-7005 on ethanol and glucose mixture].

The possibility of elimination of C2-metabolism limitation under Acinetobacter sp. B-7005 (producer of exopolysaccharide ethapolan) cultivation on ethanol-glucose mixture was shown. Cultivation of these bacteria on the nonbuffered medium was accompanied by pH decrease (5.6-4.7), acetate accumulation (25-45 mM), drop in the biomass and exopolysaccharide concentration. The decrease of the ammonium nitrate content (to 0.3 g/l) in the medium, its replacement by nitrate, the increase of the pantotenate calcium concentration to 0.0009%, potassium and magnesium cations to 100 and 5-10 mM, application of the inoculum grown on acetate or ethanol, the decrease of the substrates initial concentration to 0.25% permitted a prevention of acetate accumulation and realization of ethanol synthesis on ethanol-glucose mixture on the inbuffered medium.

Acinetobacter↗
PubMedDate not supplied

[Antimicrobial susceptibility of phenotypically extended spectrum beta-lactamase producing Pseudomonas aeruginosa and Acinetobacter baumannii isolates].

The aim of this study was to investigate the antimicrobial susceptibilities of Pseudomonas aeruginosa and Acinetobacter baumannii strains that were identified as producers of extended spectrum beta-lactamases (ESBL) phenotypically. Fifty three P. aeruginosa and 53 A. baumannii strains that were isolated from patients with hospital infections followed-up by Infectious Diseases Unit of Hacettepe University Adult Hospital in 2002-2004, were included in the study. The susceptibilities of the isolates to ceftazidime, cefotaxime, cefepime, tobramycin, ciprofloxacin, piperacillin-tazobactam, imipenem and meropenem were determined by Etest (AB Biodisk, Solna, Sweden) method. The susceptibility rates of A. baumannii isolates against tobramycin and carbapenem group were 54.7% and 49.1%, respectively; whereas for the rest of the antimicrobial agents tested, these rates were lower than 25 percent. The susceptibility rates of P. aeruginosa isolates against ciprofloxacin, carbapenem group, piperacillin-tazobactam and tobramycin differed between 35-38 percent. Of the P. aeruginosa isolates, 37.5%, and of the A. baumannii isolates 37.7% were resistant against imipenem/meropenem, piperacillin-tazobactam, ciprofloxacin and tobramycin simultaneously. As a result, phenotypically ESBL producing P. aeruginosa and A. baumannii isolates were found highly resistant not only against the third and fourth generation cephalosporins, but also to the antibiotics currently used in the therapy including carbapenemes.

Acinetobacter baumannii↗
PubMed2006

[Factors predicting metallo-beta-lactamase-producing Acinetobacter baumannii in Iwate Medical University Hospital].

We conducted a decision tree analysis in which 6 isolates of metallo-beta-lactamase (MBL) -producing Acinetobacter baumannii detected by a sodium mercaptoacetic acid disk method and 38 isolates of MBL nonproducing A. baumannii were investigated from January 2003 to December 2003 in Iwate Medical University Hospital. Factors predicting MBL-producing A. baumannii were analyzed from the clinical backgrounds such as laboratory data, therapeutic histories and bacterial circumstances. In the decision tree analysis, seven significant rules were found for predicting MBL-producing A. baumannii; previous isolation of P. aeruginosa, administration period of 3rd generation cephem antibiotics > 11 days, both TP < or = 6.9 g/dl and Hb < or = 6.3 g/dl, both administration of anticancer drugs and a use of respirator, TP > 6.9 g/dl, CRP > 22.7 mg/dl, both CRP 8.7 mg/dl and body temperature > 36.6 degrees C. Two cases, which were matched with the rule of TP > 6.9 g/dl, were hospitalized in the same division, and their pulsed-field gel electrophoresis patterns were identical. In comparison with conventional statistical analysis, the decision tree analysis has advantages in explaining the tendencies and the relationships of the data. It is possible that, based on the rules extracted in this study, we could issue precautions in preventing nosocomial MBL-producing strains even in the earlier stages when the number of these isolates are still small.

Acinetobacter baumannii↗