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At least 19 recordsLinked to original sources
PubMed2004

Resistance to imipenem, cefepime, and cefpirome associated with mutation in Omp36 osmoporin of Enterobacter aerogenes.

Enterobacter aerogenes develops increased multidrug resistance via a functional alteration of outer-membrane permeability associated with a decrease in porin function. We have sequenced the gene coding the major porin of Enterobacter aerogenes, omp36. The sequence shows a high similarity with the Klebsiella pneumoniae ompK36 gene and is closely related to the enterobacterial OmpC family. Sequence analysis of several Omp36 issued from clinical strains indicated variability in putative cell-surface exposed domains. Interestingly, substitution Gly112Asp was observed in the conserved eyelet L3 region of the porin produced by two strains, C and 3. This substitution is associated with a high general beta-lactam resistance observed in these isolates and with alteration of pore properties previously described in strain 3 porin [Mol. Microbiol. 41 (2001) 189]. This is the first genetic identification of impermeability-mediated resistance to beta-lactams in various clinical E. aerogenes strains.

Bacterial Outer Membrane Proteins↗
PubMed2004

TEM-121, a novel complex mutant of TEM-type beta-lactamase from Enterobacter aerogenes.

Enterobacter aerogenes clinical isolate LOR was resistant to penicillins and ceftazidime but susceptible to cefuroxime, cephalothin, cefoxitin, cefotaxime, ceftriaxone, and cefepime. PCR and cloning experiments from this strain identified a novel TEM-type beta-lactamase (TEM-121) differing by five amino acid substitutions from beta-lactamase TEM-2 (Glu104Lys, Arg164Ser, Ala237Thr, Glu240Lys, and Arg244Ser) and by only one amino acid change from the extended-spectrum beta-lactamase (ESBL) TEM-24 (Arg244Ser), with the last substitution also being identified in the inhibitor-resistant beta-lactamase IRT-2. Kinetic parameters indicated that TEM-121 hydrolyzed ceftazidime and aztreonam (like TEM-24) and was inhibited weakly by clavulanic acid and strongly by tazobactam. Thus, TEM-121 is a novel complex mutant TEM beta-lactamase (CMT-4) combining the kinetic properties of an ESBL and an inhibitor-resistant TEM enzyme.

Ceftazidime↗
PubMed1998

Porin alteration and active efflux: two in vivo drug resistance strategies used by Enterobacter aerogenes.

Enterobacter aerogenes is among the five most frequently isolated nosocomial pathogens in France, and this bacterium also shows increasing multidrug resistance. In this study, various E. aerogenes strains isolated from hospital units were characterized for their outer-membrane proteins, antibiotic susceptibilities (inhibition diameters and MICs) and resistance mechanisms associated with modification of envelope permeability (porin alteration and active efflux). Diminished outer-membrane permeability due to porin alterations was found in conjunction with the expression of an enzymic barrier in resistant isolates. Interestingly, changes in the functional expression of porins appeared to play a special role in susceptibility to cefepime. An active efflux to quinolones was also identified. Simultaneous changes in envelope permeability, i.e. a porin deficiency (in) and an efflux mechanism (out), were clearly evident in two clinical strains.

Anti-Bacterial Agents↗
PubMed1977

Energy-dependent inactivation of citrate lyase in Enterobacter aerogenes.

Enterobacter aerogenes was grown in continous culture with ammonia as the growth-limiting substrate, and changes in citrate lyase and citrate synthase activities were monitored after growth shifts from anaerobic growth on citrate to aerobic growth on citrate, aerobic growth on glucose, anaerobic growth on glucose, and anaerobic growth on glucose plus nitrate. Citrate lyase was inactivated during aerobic growth on glucose and during anaerobic growth with glucose plus nitrate. Inactivation did not occur during anaerobic growth on glucose, and as a result of the simultaneous presence of citrate lyase and citrate synthase, growth difficulties were observed. Citrate lyase inactivation consisted of deacetylation of the enzyme. The corresponding deacetylase could not be demonstrated in cell extracts, and it is concluded that, as in a number of other inactivations, electron transport to oxygen or nitrate was required for inactivation.

Aerobiosis↗
PubMedDate not supplied

[Application of gas chromatography in the identification of Enterobacter cloacae, Enterobacter aerogenes, and Enterobacter agglomerans].

Enterobacter cloacae, Enterobacter aerogenes and Enterobacter agglomerans were identified using gas chromatography as a substitution of the traditional techniques. Their acid methyl esters profiles were determined using a gas chromatograph Hewlett Packard 5890A and a RSL-150 heliflex capillary column. A total of 120 samples were analyzed from reference strains (ATCC 13047, 13048, 27155) and environmental isolations, eleven fatty acids were included in the profiles from which cis-9, 10-methyleneoctadecanoic acid (peak 24), cis-9-hexadecenoic acid (peak 14), octadecanoic acid (peak 23) and dodecanoic acid (peak 3), were the most important for the differentiation of the three species analyzed.

Bacteriological Techniques↗
PubMed2002

Natural antibiotic susceptibility of Enterobacter spp., with special reference to Enterobacter aerogenes and Enterobacter intermedius strains.

The natural susceptibility to 71 antibiotics of 44 strains of Enterobacter aerogenes and 12 strains of Enterobacter intermedius was examined using a microdilution procedure in Isosensitest broth (for all strains) and cation-adjusted Mueller Hinton broth (for some strains). Both species were naturally sensitive or sensitive and intermediate to tetracyclines, all tested aminoglycosides, several penicillins and cephalosporins, carbapenems, aztreonam, quinolones, folate-pathway inhibitors, chloramphenicol and nitrofurantoin. Uniform natural resistance was found to cefoxitin and to antibiotics to which most other Enterobacteriaceae are also intrinsically resistant, e.g. several macrolides, lincosamides, streptogramins and glycopeptides. Major species-specific differences in susceptibility affecting clinical assessment criteria were found with amoxycillin, amoxycillin-clavulanate, some narrow-spectrum cephalosporins and fosfomycin. With the exception of penicillin G, oxacillin and cefoxitin, E. intermedius was naturally sensitive or naturally sensitive and intermediate (azlocillin) to all beta-lactams tested. Natural antibiotic susceptibility patterns of E. aerogenes and E. intermedius were analyzed with regard to the underlying mechanisms. The data were compared with the results from two recent studies dealing with natural susceptibilities of other clinically-relevant Enterobacter spp. With reference to beta-lactam susceptibility patterns, it can be assumed that all human-affecting Enterobacter species examined produce species-specific, chromosomally-encoded beta-lactamases of the AmpC type. The naturally-expressed amount of enzyme depends on the species.

Anti-Bacterial Agents↗
PubMed1994

Detection of resistance due to inducible beta-lactamase in Enterobacter aerogenes and Enterobacter cloacae.

Thirty-six of 36 strains of Enterobacter cloacae and E. aerogenes with inducible beta-lactamase developed resistance when cefoxitin (inducer) was added to cefuroxime disks. Constitutive beta-lactamase producers (n = 23) were all resistant to cefuroxime. Cefuroxime resistance correlated with the amount of induced or constitutive beta-lactamase. Cefuroxime was a better indicator of induced resistance than cefamandole, cefazolin, cephalothin, ceftriaxone, cefotaxime, ticarcillin with or without clavulanic acid, or cefotetan. Induction by addition of cefoxitin to disks occasionally reduced zone sizes but not enough to change interpretations for ceftazidime, ceftizoxime, aztreonam, cefoperazone with or without sulbactam, and piperacillin with or without tazobactam. Most enterobacters were resistant to cefmetazole. The cefoxitin inducer-cefuroxime indicator method can be used in routine clinical laboratories to detect latent resistance due to chromosomally mediated inducible beta-lactamase in enterobacters.

Cefuroxime↗
PubMed2005

The eefABC multidrug efflux pump operon is repressed by H-NS in Enterobacter aerogenes.

The Enterobacter aerogenes eefABC locus, which encodes a tripartite efflux pump, was cloned by complementation of an Escherichia coli tolC mutant. E. aerogenes deltaacrA expressing EefABC became less susceptible to a wide range of antibiotics. Data from eef::lacZ fusions showed that eefABC was not transcribed in the various laboratory conditions tested. However, increased transcription from Peef was observed in an E. coli hns mutant. In addition, EefA was detected in E. aerogenes expressing a dominant negative E. coli hns allele.

Bacterial Outer Membrane Proteins↗
PubMed2002

Inhibitors of antibiotic efflux pump in resistant Enterobacter aerogenes strains.

Enterobacter aerogenes, a nosocomial pathogen, is frequently exhibiting multidrug resistance mechanisms associated with a change in membrane permeability. In clinical isolates, active efflux plays a prominent role in antibiotic resistance. We report here the effect of three unrelated compounds that are able to restore a noticeable antibiotic susceptibility to resistant strains. The targeting of various parameters which contribute to the efficacy of the efflux mechanism, such as energy, flux selectivity, or functional assembly of the membrane complex, increases the intracellular chloramphenicol concentration in resistant isolates.

Anti-Bacterial Agents↗
PubMed2001

New pyridoquinoline derivatives as potential inhibitors of the fluoroquinolone efflux pump in resistant Enterobacter aerogenes strains.

Enterobacter aerogenes, one of the most frequently isolated nosocomial pathogens in France, is exhibiting increasing multidrug resistance mechanisms associated with a change in membrane permeability. For drugs of the quinolone family, mutations in the target and active efflux play a prominent role in the resistance. We report here the effect of several pyridoquinoline derivatives that restore a noticeable fluoroquinolone accumulation to resistant strains that overexpress the MarA activator. Studies of the energy-dependent quinolone efflux indicate that the most efficient derivatives tested probably inhibit the resistance process by acting as substrate competitors on the pump extruding intracellular norfloxacin.

Anti-Infective Agents↗
PubMed1975

Physiological and biochemical role of the butanediol pathway in Aerobacter (Enterobacter) aerogenes.

Aerobacter (Enterobacter) aerogenes wild type and three mutants deficient in the formation of acetoin and 2,3-butanediol were grown in a glucose minimal medium. Culture densities, pH, and diacetyl, acetoin, and 2,3-butanediol levels were recorded. The pH in wild-type cultures dropped from 7.0 to 5.8, remained constant while acetoin and 2,3-butanediol were formed, and increased to pH 6.5 after exhaustion of the carbon source. More 2,3-butanediol than acetoin was formed initially, but after glucose exhaustion reoxidation to acetoin occurred. The three mutants differed from the wild type in yielding acid cultures (pH below 4.5). The wild type and one of the mutants were grown exponentially under aerobic and anaerobic conditions with the pH fixed at 7.0, 5.8, and 5.0, respectively. Growth rates decreased with decreasing pH values. Aerobically, this effect was weak, and the two strains were affected to the same degree. Under anaerobic conditions, the growth rates were markedly inhibited at a low pH, and the mutant was slightly more affected than the wild type. Levels of alcohol dehydrogenase were low under all conditions, indicating that the enzyme plays no role during exponential growth. The levels of diacetyl (acetoin) reductase, lactate dehydrogenase, and phosphotransacetylase were independent of the pH during aerobic growth of the two strains. Under anaerobic conditions, the formation of diacetyl (acetoin) reductase was pH dependent, with much higher levels of the enzyme at pH 5.0 than at pH 7.0. Lactate dehydrogenase and phosphotransacetylase revealed the same pattern of pH-dependent formation in the mutant, but not in the wild type.

Acetates↗
PubMed2003

4-alkoxy and 4-thioalkoxyquinoline derivatives as chemosensitizers for the chloramphenicol-resistant clinical Enterobacter aerogenes 27 strain.

Enterobacter aerogenes is a Gram-negative bacteria frequently responsible for nosocomial respiratory tract infections. Strains resistant to chloramphenicol are frequently isolated. Alkoxy and thio-alkoxyquinolines have a potential to act as chemosensitizers that would render multi-drug-resistant (MDR) bacterial infections susceptible to antibiotics to which they were originally resistant. Several new quinoline derivatives have been prepared, characterized and studied for their ability to increase chloramphenicol sensitivity of E. aerogenes 27, a clinical strain that exhibits the MDR phenotype. Drugs investigated were either quinoline ethers or quinoline thio-ethers. Thio-ethers are much more efficient in increasing chloramphenicol sensitivity than other corresponding ethers. In particular, 4-piperidinoethylthio-quinoline increases the strain sensitivity to chloramphenicol by about 20 times at 2 mM concentration. Similarly, sensitivity to quinolone antibiotics dramatically increases. Because these quinoline derivatives act as inhibitors of the drug efflux pump responsible for bacterial resistance to chloramphenicol, they may serve as adjunct to conventional therapy of E. aerogenes infections.

Anti-Bacterial Agents↗
PubMed2004

Selection during cefepime treatment of a new cephalosporinase variant with extended-spectrum resistance to cefepime in an Enterobacter aerogenes clinical isolate.

Enterobacter aerogenes resistant to cefepime (MIC, 32 microg/ml) was isolated from a patient treated with cefepime for an infection caused by a strain of E. aerogenes overproducing its AmpC beta-lactamase (MIC of cefepime, 0.5 microg/ml). The AmpC beta-lactamase of the resistant strain had an L-293-P amino acid substitution and a high k(cat)/K(m) ratio for cefepime. Both of these modifications were necessary for resistance to cefepime.

Amino Acid Sequence↗
PubMed2002

Chemical modification of specific active site amino acid residues of Enterobacter aerogenes glycerol dehydrogenase.

Enterobacter aerogenes glycerol dehydrogenase (G1DH EC 1.1.1.6), a tetrameric NAD+ specific enzyme catalysing the interconversion of glycerol and dihydroxyacetone, was inactivated on reaction with pyridoxal 5-phosphate (PLP) and o-phthalaldehyde (OPA). Fluorescence spectra of PLP-modified, sodium borohydride-reduced G1DH indicated the specific modification of epsilon-amino groups of lysine residues. The extent of inhibition was concentration and time dependent. NAD+ and NADH provided complete protection against enzyme inactivation by PLP, indicating the reactive lysine is at or near the coenzyme binding site. Modification of G1DH by the bifunctional reagent OPA, which reacts specifically with proximal epsilon-NH2 group of lysines and -SH group of cysteines to form thioisoindole derivatives, inactivated the enzyme. Molecular weight determinations of the modified enzyme indicated the formation of intramolecular thioisoindole formation. Glycerol partially protected the enzyme against OPA inactivation, whereas NAD+ was ineffective. These results show that the lysine involved in the OPA reaction is different from the PLP-reactive lysine, which is at or near the coenzyme binding site. DTNB titration showed the presence of only a single cysteine residue per monomer of G1DH. This could be participating with a proximal lysine residue to form a thioisoindole derivative observed as a result of OPA modification.

Amino Acids↗
PubMed1988

Detection of carbon-phosphorus lyase activity in cell free extracts of Enterobacter aerogenes.

The bacterium Enterobacter aerogenes could grow on a medium containing alkylphosphonic acid as a phosphorus source. The extracts prepared from the cells grown on phosphonoacetic acid as a sole source of phosphorus showed an activity of carbon-phosphorus lyase and hydrolyzed methyl-phosphonic acid, phosphonoacetic acid and phenylphosphonic acid with a liberation of inorganic phosphates.

Cell-Free System↗
PubMed1997

Characteristics of the melibiose transporter and its primary structure in Enterobacter aerogenes.

Cells of Enterobacter aerogenes can grow on melibiose as a sole source of carbon. This suggests the presence of melibiose operon in this organism. We found that E. aerogenes cells possess both alpha-galactosidase activity and melibiose transport activity, which were induced by melibiose. Neither Na+ nor Li+ stimulated the melibiose transport. However, transport of methyl-beta-thiogalactoside (TMG) was stimulated by Li+ but not by Na+. These findings suggest that the major coupling cation for the melibiose transporter in E. aerogenes is H+. In fact, we observed H+ entry into cells caused by an influx of melibiose and some of its analogs. We cloned the melB gene which encodes the melibiose transporter, and sequenced it. Deduced amino acid sequence of the transporter revealed that the melibiose transporter consists of 471 amino acid residues and the molecular weight was calculated to be 52214 Da. The sequence showed high homology with the sequences of the melibiose transporters of Escherichia coli, Salmonella typhimurium and Klebsiella pneumoniae. Higher homology was found with the melibiose transporter of K. pneumoniae than with that of E. coli and S. typhimurium.

Amino Acid Sequence↗
PubMed2004

RamA is an alternate activator of the multidrug resistance cascade in Enterobacter aerogenes.

Multidrug resistance (MDR) in Enterobacter aerogenes can be mediated by induction of MarA, which is triggered by certain antibiotics and phenolic compounds. In this study, we identified the gene encoding RamA, a 113-amino-acid regulatory protein belonging to the AraC-XylS transcriptional activator family, in the Enterobacter aerogenes ATCC 13048 type strain and in a clinical multiresistant isolate. Overexpression of RamA induced an MDR phenotype in drug-susceptible Escherichia coli JM109 and E. aerogenes ATCC 13048, as demonstrated by 2- to 16-fold-increased resistance to beta-lactams, tetracycline, chloramphenicol, and quinolones, a decrease in porin production, and increased production of AcrA, a component of the AcrAB-TolC drug efflux pump. We show that RamA enhances the transcription of the marRAB operon but is also able to induce an MDR phenotype in a mar-deleted strain. We demonstrate here that RamA is a transcriptional activator of the Mar regulon and is also a self-governing activator of the MDR cascade.

Amino Acid Sequence↗