hr-810 and Enterobacteriaceae-Infections

Two clinical strains of Escherichia coli (2138) and Enterobacter cloacae (7506) isolated from the same patient in France and showing resistance to extended-spectrum cephalosporins and low susceptibility to imipenem were investigated. Both strains harbored the plasmid-contained bla(TEM-1) and bla(KPC-2) genes. bla(KLUC-2), encoding a mutant of the chromosomal beta-lactamase of Kluyvera cryocrescens, was also identified at a plasmid location in E. cloacae 7506, suggesting the ISEcp1-assisted escape of bla(KLUC) from the chromosome. Determination of the KPC-2 structure at 1.6 A revealed that the binding site was occupied by the C-terminal (C-ter) residues coming from a symmetric KPC-2 monomer, with the ultimate C-ter Glu interacting with Ser130, Lys234, Thr235, and Thr237 in the active site. This mode of binding can be paralleled to the inhibition of the TEM-1 beta-lactamase by the inhibitory protein BLIP. Determination of the 1.23-A structure of a KPC-2 mutant in which the five C-ter residues were deleted revealed that the catalytic site was filled by a citrate molecule. Structure analysis and docking simulations with cefotaxime and imipenem provided further insights into the molecular basis of the extremely broad spectrum of KPC-2, which behaves as a cefotaximase with significant activity against carbapenems. In particular, residues 104, 105, 132, and 167 draw a binding cavity capable of accommodating both the aminothiazole moiety of cefotaxime and the 6 alpha-hydroxyethyl group of imipenem, with the binding of the former drug being also favored by a significant degree of freedom at the level of the loop at positions 96 to 105 and by an enlargement of the binding site at the end of strand beta 3.

Topics: Aged; Base Sequence; beta-Lactam Resistance; beta-Lactamases; beta-Lactams; Catalytic Domain; Cephalosporin Resistance; Crystallography, X-Ray; DNA Primers; DNA, Bacterial; Enterobacter cloacae; Enterobacteriaceae Infections; Escherichia coli; Escherichia coli Infections; France; Genes, Bacterial; Humans; Imipenem; Kinetics; Male; Models, Molecular; Mutation

Citrobacter freundii strain 4306 was isolated from a urine specimen of a patient in March 2006 in Palestine. This strain showed a unique multidrug resistance phenotype, as it was resistant both to 7-alpha-methoxy- and oxyimino-cephalosporins, including cefepime, cefpirome and monobactams, in addition to quinolones, streptomycin and trimethoprim/sulfamethoxazole. Clavulanic acid did not act synergistically with cephalosporins by the double-disk synergy test. Molecular characterisation showed that the resistance to 7-alpha-methoxy- and oxyimino-cephalosporins was due to a novel AmpC beta-lactamase, designated CMY-37, with an isoelectric point of approximately 9.0. CMY-37 is a variant of C. freundii chromosomal AmpC enzymes with at least seven amino acid substitutions. One of these substitutions, L316I, is located within the R2 loop that is considered the hotspot region responsible for the extended substrate spectrum in class C beta-lactamases. The blaCMY-37 gene was cloned and expressed in Escherichia coli TG1. CMY-37 is chromosomally encoded and is not associated with ISEcp1-like element. Phylogenetic analysis suggested that CMY-37 is the origin of many plasmid-mediated AmpC beta-lactamases. This study highlights the emergence of cefepime and cefpirome resistance in C. freundii owing to a new type of AmpC beta-lactamase.

Topics: Amino Acid Sequence; Anti-Bacterial Agents; Bacterial Proteins; beta-Lactam Resistance; beta-Lactamases; Cefepime; Cefpirome; Cephalosporin Resistance; Cephalosporins; Chromosomes, Bacterial; Citrobacter freundii; Enterobacteriaceae Infections; Humans; Microbial Sensitivity Tests; Molecular Sequence Data; Phylogeny

Enterobacter cloacae CHE, a clinical strain with overproduced cephalosporinase was found to be highly resistant to the new cephalosporins, cefepime and cefpirome (MICs> or =128 microg ml(-1)). The strain was isolated from a child previously treated with cefepime. The catalytic efficiency of the purified enzyme with the third-generation cephalosporins, cefepime and cefpirome, was 10 times higher than that with the E. cloacae P99 enzyme. This was mostly due to a decrease in K(m) for these beta-lactams. The clinical isolate produced large amounts of the cephalosporinase because introduction of the ampD gene decreased ampC expression and partially restored the wild-type phenotype. Indeed, MICs of cefepime and cefpirome remained 10 times higher than those for a stable derepressed clinical isolate (OUDhyp) transformed with an ampD gene. Sequencing of the ampC gene showed that 18 nucleotides had been deleted, corresponding to the six amino acids SKVALA (residues 289--294). According to the crystal structure of P99 beta-lactamase, this deletion was located in the H-10 helix. The ampR-ampC genes from the clinical isolates CHE and OUDhyp were cloned and expressed in Escherichia coli JM101. The MICs of cefpirome and cefepime of E. coli harboring ampC and ampR genes from CHE were 100--200 times higher than those of E. coli harboring ampC and ampR genes from OUDhyp. This suggests that the deletion, confirmed by sequencing of the ampC gene, is involved in resistance to cefepime and cefpirome. However, the high level of resistance to cefepime and cefpirome observed in the E. cloacae clinical isolate was due to a combination of hyperproduction of the AmpC beta-lactamase and structural modification of the enzyme. This is the first example of an AmpC variant conferring resistance to cefepime and cefpirome, isolated as a clinical strain.

Topics: Amino Acid Sequence; Bacterial Proteins; Base Sequence; beta-Lactamases; Cefepime; Cefpirome; Cephalosporin Resistance; Cephalosporinase; Cephalosporins; Child; Cloning, Molecular; Enterobacter cloacae; Enterobacteriaceae Infections; Escherichia coli; Genes, Bacterial; Humans; Kinetics; Microbial Sensitivity Tests; Molecular Sequence Data; Protein Structure, Secondary; Recombinant Proteins; Sequence Deletion

Multidrug-resistant Enterobacter aerogenes strains are increasingly isolated in Europe and especially in France. Treatment leads to imipenem resistance, because of a lack of porin. We studied the evolution of resistance in 29 strains isolated from four patients during their clinical course. These strains belonged to the prevalent epidemiological type observed in France in previous studies (C. Bosi, et al., J. Clin. Microbiol. 37:2165-2169, 1999; A. Davin-Regli et al., J. Clin. Microbiol. 34:1474-1480, 1996). They also harbored a TEM-24 extended-spectrum beta-lactamase-coding gene. Thirteen strains were susceptible to gentamicin and resistant to imipenem and cefepime. All of the patients showed E. aerogenes strains with this resistance after an imipenem treatment. One patient showed resistance to imipenem after a treatment with cefpirome. Twelve of these 13 strains showed a lack of porin. Cessation of treatment with imipenem for three patients was followed by reversion of susceptibility to this antibiotic and the reappearance of porins, except in one case. For one patient, we observed three times in the same day the coexistence of resistant strains lacking porin and susceptible strains possessing porin. The emergence of multidrug-resistant E. aerogenes strains is very disquieting. In our study, infection by E. aerogenes increased the severity of the patients' illnesses, causing a 100% fatality rate.

Topics: Bacterial Typing Techniques; beta-Lactamases; Cefpirome; Cell Membrane Permeability; Cephalosporins; Drug Resistance, Microbial; Enterobacter; Enterobacteriaceae Infections; Fatal Outcome; France; Humans; Imipenem; Male; Microbial Sensitivity Tests; Thienamycins; Trachea; Urine

Increasing antimicrobial resistance has been reported for Klebsiella spp. and Enterobacter spp. The in-vitro activities of 14 antimicrobial agents against 656 clinical isolates of Klebsiella spp. and 630 isolates of Enterobacter spp. collected from seven cities in Canada were determined by microbroth dilution. There was no regional variation in the susceptibility patterns. Klebsiella spp. remain highly susceptible to most antimicrobials, only one isolate was resistant to third-generation cephalosporins. However, many isolates of Enterobacter spp. (> 16%) were resistant to the third-generation cephalosporins with marked cross-resistance to piperacillin (63.1%), piperacillin/tazobactam (44.9%), and aztreonam (76.6%). Gentamicin, tobramycin, imipenem, ciprofloxacin, cefepime, and cefpirome were consistently active against most isolates of Enterobacter spp. including those resistant to the third-generation cephalosporins.

Topics: Anti-Bacterial Agents; Canada; Cefepime; Cefpirome; Cephalosporins; Drug Resistance, Microbial; Enterobacter; Enterobacteriaceae Infections; Humans; Klebsiella; Klebsiella Infections; Microbial Sensitivity Tests

In systemic and local infections, the therapeutic efficacy of cefpirome was compared to that of imipenem and cefotaxime. Murine septicemia induced with methicillin-sensitive and methicillin-resistant Staphylococcus aureus strains responded well to cefpirome and imipenem therapy, the ED50 values ranged from 0.8 to 28.40 mg/kg and 0.5 to 15.58 mg/kg, respectively. The carbapenem also displayed high efficacy against Enterococci and was more potent than cefpirome. Cefotaxime, however, exhibited lower activity or proved to be inactive against these strains. With ED50 values of 0.03 to 31.33 mg/kg, cefpirome was the most active of the three antibiotics in protecting mice challenged with Enterobacteriaceae. The corresponding ED50 values of imipenem and cefotaxime ranged from 0.72 to 70.95 mg/kg and 0.06 to 66.30 mg/kg, respectively. Despite distinctly lower in vitro activity against the infecting organism, cefpirome showed efficacy similar to imipenem in the treatment of subcutaneous S. aureus abscesses in mice. It was more effective than imipenem and cefotaxime against experimental Klebsiella pneumonia in mice and the Escherichia coli infected granuloma pouch in rats.

Topics: Abscess; Animals; Bacterial Infections; Cefotaxime; Cefpirome; Cephalosporins; Enterobacteriaceae Infections; Escherichia coli Infections; Female; Granuloma; Imipenem; Male; Mice; Mice, Hairless; Mice, Inbred C3H; Pneumonia; Rats; Rats, Inbred Strains; Sepsis; Staphylococcal Skin Infections; Staphylococcus aureus; Streptococcal Infections