Corynebacterium hansenii sp. nov., an alpha-glucosidase-negative bacterium related to Corynebacterium xerosis.

A novel strain, C-138(T), belonging to the genus Corynebacterium was isolated from a severe thigh liposarcoma infection and its differentiation from Corynebacterium xerosis and Corynebacterium freneyi is described. Analysis of 16S rRNA gene sequences, rpoB sequences and the PCR profile of the 16S-23S spacer regions was not conclusive enough to differentiate strain C-138(T) from C. xerosis and C. freneyi. However, according to DNA-DNA hybridization data, strain C-138(T) constitutes a member of a distinct novel species. It can be differentiated from strains of C. xerosis and C. freneyi by colony morphology, the absence of alpha-glucosidase and some biochemical characteristics such as glucose fermentation at 42 degrees C and carbon assimilation substrates. The name Corynebacterium hansenii sp. nov. is proposed for this novel species; the type strain is C-138(T) (=CIP 108444(T)=CCUG 53252(T)).

Identification of an OprD homologue in Acinetobacter baumannii.

With the increased number of resistant Acinetobacter baumannii strains, it is urgently required to decipher the molecular bases of outer membrane permeability. The analyses of the outer membrane from different A. baumannii strains indicated a modification in the expression of two proteins of 29 and 43 kDa, respectively. By electrophoresis and MALDI-MS analyses, the 43 kDa OMP was identified as a protein belonging to the OprD family, a basic amino acid and imipenem porin.

Successive emergence of Enterobacter aerogenes strains resistant to imipenem and colistin in a patient.

Enterobacter aerogenes is an agent of hospital-acquired infection that exhibits a remarkable resistance to beta-lactam antibiotics during therapy. Five successive isolates of E. aerogenes infecting a patient and exhibiting a multiresistance phenotype to beta-lactam antibiotics and fluoroquinolones were investigated. Among these clinical strains, four presented resistant phenotypes during successive imipenem and colistin treatments. The involved resistance mechanisms exhibited by the successive isolates were associated with alterations of the outer membrane that caused a porin decrease and lipopolysaccharide modifications.

Aeromonas popoffii urinary tract infection.

Aeromonas popoffii is a recently described species isolated mainly from freshwater. An isolate of Aeromonas popoffii was found to be responsible for a urinary tract infection in a 13-year-old boy suffering from spina bifida with enterocystoplasty. This is the first reported case of human infection attributed to this species.

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.

Omp35, a new Enterobacter aerogenes porin involved in selective susceptibility to cephalosporins.

In Enterobacter aerogenes, beta-lactam resistance often involves a decrease in outer membrane permeability induced by modifications of porin synthesis. In ATCC 15038 strain, we observed a different pattern of porin production associated with a variable antibiotic susceptibility. We purified Omp35, which is expressed under conditions of low osmolality and analyzed its pore-forming properties in artificial membranes. This porin was found to be an OmpF-like protein with high conductance values. It showed a noticeably higher conductance compared to Omp36 and a specific location of WNYT residues in the L3 loop. The importance of the constriction region in the porin function suggests that this organization is involved in the level of susceptibility to negative large cephalosporins such as ceftriaxone by bacteria producing the Omp35 porin subfamily.

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.

Corynebacterium freneyi bacteremia.

Corynebacterium freneyi is a recently described alpha-glucosidase-positive species of the genus CORYNEBACTERIUM: To our knowledge, there is no description of human infection due to this species. We report on a case of bacteremia due to C. freneyi following vascular surgery.

Eubacterium callanderi bacteremia: report of the first case.

Eubacterium callanderi is an environmental anaerobic rod-shaped bacterium first isolated in 1998 from an industrial anaerobic digester. We report on the first clinical isolate of E. callanderi, which was recovered from the blood of a patient with a bladder carcinoma. Identification of the organism was made by cell fatty acid chromatographic analysis and 16S rRNA gene sequencing.

Imipenem and expression of multidrug efflux pump in Enterobacter aerogenes.

Imipenem is often used to treat intensive care unit patients infected by Enterobacter aerogenes, but it is leading to an increasing number of antibiotic resistant strains. Clinical isolates and imipenem resistant variants presented a high level of resistance to beta-lactam antibiotic group and to chemically unrelated drugs. We report here that imipenem selects strains which contain active efflux pumps ejecting various unrelated antibiotics including quinolones, tetracycline, and chloramphenicol. An increase of AcrA, an efflux pump component, was observed in the imipenem resistant variants. The overexpression of marA, involved in the genetic control of membrane permeability via porin and efflux pump expression, indicated the activation of the resistance genetic cascade in imipenem resistant variants.

prbA, a gene coding for an esterase hydrolyzing parabens in enterobacter cloacae and Enterobacter gergoviae strains.

The new gene prbA encodes an esterase responsible for the hydrolysis of the ester bond of parabens in Enterobacter cloacae strain EM. This gene is located on the chromosome of strain EM and was cloned by several PCR approaches. The prbA gene codes for an immature protein of 533 amino acids, the first 31 of which represent a proposed signal peptide yielding a mature protein of a putative molecular mass of 54.6 kDa. This enzyme presents analogies with other type B carboxylesterases, mainly of eukaryotic origin. The cloning and expression of the prbA gene in a strain of Escherichia coli previously unable to hydrolyze parabens resulted in the acquisition of a hydrolytic capacity comparable to the original activity of strain EM, along with an increased resistance of the transformed strain to methyl paraben. The presence of homologues of prbA was tested in additional ubiquitous bacteria, which may be causative factors in opportunistic infections, including Enterobacter gergoviae, Enterobacter aerogenes, Pseudomonas agglomerans, E. coli, Pseudomonas aeruginosa, and Burkholderia cepacia. Among the 41 total strains tested, 2 strains of E. gergoviae and 1 strain of Burkholderia cepacia were able to degrade almost completely 800 mg of methyl paraben liter(-1). Two strains of E. gergoviae, named G1 and G12, contained a gene that showed high homology to the prbA gene of E. cloacae and demonstrated comparable paraben esterase activities. The significant geographical distance between the locations of the isolated E. cloacae and E. gergoviae strains suggests the possibility of an efficient transfer mechanism of the prbA gene, conferring additional resistance to parabens in ubiquitous bacteria that represent a common source of opportunistic infections.

mar Operon involved in multidrug resistance of Enterobacter aerogenes.

We determined the sequence of the entire marRAB operon in Enterobacter aerogenes. It is functionally and structurally analogous to the Escherichia coli operon. The overexpression of E. aerogenes MarA induces a multidrug resistance phenotype in a susceptible strain, demonstrated by a noticeable resistance to various antibiotics, a decrease in immunodetected porins, and active efflux of norfloxacin.

Molecular characterization of amoxicillin-clavulanate resistance in a clinical isolate of Escherichia coli.

The resistance phenotype of the clinical isolate of Escherichia coli 1941 was characterized by high-level resistance to penicillins and to combinations amoxicillin-ticarcillin/clavulanate and ampicillin/sulbactam. This resistance was carried by the conjugative plasmid pEC1941 that encoded a beta-lactamase activity. The purified enzyme focused at pI 5.4 and was strongly inhibited in vitro by clavulanic acid (IC50 = 0.09 microM). Nucleotide sequence analysis revealed identity between the plasmid borne blaTEM gene of E. coli 1941 and the blaTEM-1B gene, except for a single C-to-T substitution at position 32 in the promoter region leading to the overlapping promoters Pa and Pb. No alterations in the expression of outer membrane porins OmpC and OmpF have been detected. These findings show that the resistance of E. coli 1941 to the combinations of beta-lactams with beta-lactamase inhibitors is related to high-level production of TEM-1 enzyme expressed from the strong promoters Pa and Pb.

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.