Vincent Cattoir

Is plasmid-mediated quinolone resistance a clinically significant problem?

Although resistance to quinolones is commonly chromosomally-encoded in Enterobacteriaceae, the emergence of plasmid-mediated quinolone resistance (PMQR) has also been reported, with at least three known resistance mechanisms to date, i.e., Qnr, aminoglycoside acetyltransferase AAC(6)-Ib-cr and QepA. Qnr proteins protect target enzymes (DNA gyrase and type IV topoisomerase) from quinolone inhibition, the AAC(6)-Ib-cr enzyme acetylates norfloxacin and ciprofloxacin, and the QepA efflux pump extrudes hydrophilic fluoroquinolones. Although these PMQR determinants confer only low-level resistance to quinolones and/or fluoroquinolones, they may provide a favourable background in which the selection of additional chromosomally-encoded quinolone resistance mechanisms can occur.

Plasmid-mediated quinolone resistance determinants among enterobacterial isolates from outpatients in Brazil

OBJECTIVESnThe aim of this study was to determine the spread of plasmid-mediated quinolone resistance determinants [qnr-like, aac(6)-Ib-cr and qepA genes] among nalidixic acid-resistant enterobacterial strains isolated from outpatients from Southeast Brazil, their transferability and the genetic structures associated with the qnr genes.nnnMETHODSnThe qnrA, qnrB and qnrS genes were screened by a multiplex PCR-based technique from 257 non-repetitive nalidixic acid-resistant enterobacterial isolates collected from January 2000 to May 2005. Conjugation experiments were performed to determine whether the qnr-carrying plasmids were self-transferable. Genetic structures surrounding the qnr genes were analysed by PCR and cloning. The aac(6)-Ib-cr and qepA genes were screened among qnr-positive strains.nnnRESULTSnSix qnrB-like-positive isolates (2.3%) were detected, whereas no qnrA- or qnrS-positive isolates were detected. Three Escherichia coli and two Klebsiella pneumoniae isolates harboured a qnrB2 gene and a single Citrobacter freundii isolate had the qnrB8 gene. One qnrB2-positive isolate also had the extended-spectrum beta-lactamase bla(CTX-M-2) gene. All these isolates also possessed chromosomal substitutions in gyrase- and topoisomerase-encoding genes, explaining their high-level resistance to quinolones.nnnCONCLUSIONSnThis study constitutes the first epidemiological survey of the three known Qnr determinants among Brazilian isolates and shows their low prevalence in that country, with the qnrB2 gene being mostly identified.

Clinical impact of a real-time PCR assay for rapid identification of Staphylococcus aureus and determination of methicillin resistance from positive blood cultures

The full identification and susceptibility profile of staphylococci from positive blood cultures (BCs) generally takes 24-48 h using phenotypic methods. The aim of this prospective study was to evaluate the clinical impact of a real-time PCR strategy for rapid identification of staphylococci and determination of methicillin resistance directly from positive BCs. During a 12-month period, 250 episodes of positive BCs with organism morphology resembling staphylococci were enrolled. Two strategies were compared: conventional (n = 128) using standard phenotypic methods or rapid (n = 122) using a real-time PCR assay that is able to detect specific genes of Staphylococcus aureus (nuc and sa442) and the encoding gene for methicillin resistance (mecA). Overall, 97 episodes (39%) were clinical-significant bloodstream infections. The prevalence of methicillin resistance of S. aureus was 24%. A favorable outcome (defined as clinical cure with resolution of signs and no evidence of recurrence or relapse at 12 weeks follow-up) was observed in similar proportions of episodes with (58%) or without (60%) PCR testing (p 0.8). In multivariate analyses, age and infection due to methicillin-susceptible S. aureus (adjusted OR 0.96, 95% CI 0.93-0.99; and adjusted OR 3.11, 95% CI 1.12-8.65, respectively) were the unique factors independently associated with a favorable outcome. Among the 153 episodes of contaminated BCs, similar proportions received unjustified antibiotic therapy (PCR strategy: 17%, conventional testing: 10%; p 0.33). In a setting with a moderate level of methicillin-resistant S. aureus and relatively high contamination of BCs, real-time PCR testing was not beneficial compared to conventional methods.

Étude de la sensibilité aux antibiotiques de souches cliniques de Clostridium difficile isolées de 2001 à 2007 au CHU Henri-Mondor, Créteil

AIMnThe aim of this study was to determine the antimicrobial susceptibilities of Clostridium difficile clinical isolates obtained from symptomatic patients suffering from diarrhoea.nnnMETHODSnIn vitro activities of 22 antimicrobial agents were evaluated against 401 clinical isolates of C. difficile collected from patients hospitalized in a French university hospital (Henri Mondor hospital) between 2001 and 2007. The in vitro antibiotic susceptibility testing was performed using the disc diffusion method according to recommendations of the antibiogram committee of the French society for microbiology.nnnRESULTSnAll strains were found to be susceptible to metronidazole and vancomycin but resistant to clindamycin, gentamicin, and colistin. Most of them were susceptible to pristinamycin (97.8%), rifampin (94.8%), and chloramphenicol (97.3%), and variable degrees of resistance were found for erythromycin and spiramycin (72.8%), as well as for tetracycline (85.6%). Note that none of the strain was susceptible to ofloxacin, and that 80.5% of them showed a high-level resistance. For beta-lactams, all strains were resistant to tested cephalosporins, and nine isolates (2.2%) were also resistant to penicillins combined or not to a beta-lactamase inhibitor. Finally, 28 (7%) and 38 (9.5%) of tested strains were categorized intermediate and resistant to imipenem (with a heterogeneous aspect), respectively.nnnCONCLUSIONnAll tested strains were found to be susceptible to metronidazole and vancomycin which remain antimicrobial agents for the treatment of infections caused by C. difficile.