Mechanisms of fluoroquinolone resistance in E.coli isolates

Abstract number: P1474

Vasilaki O., Ntokou E., Kontodimou A., Frantzidou F., Sofianou D., Alexiou-Daniel S., Pournaras S.

Objective: Quinolone resistance is relatively common among Greek Escherichia coli isolates. The underlying quinolone resistance mechanisms were investigated in 114 ciprofloxacin (CIP) resistant E. coli isolates from individual patients in 4 Greek tertiary care hospitals.

Materials and Methods: The study included 114 single E. coli isolates from 4 Greek tertiary care hospitals. All strains were identified and tested for antibiotic susceptibility with the VITEK 2 automated system (bioMérieux, Marcy l'Etoile, France). All isolates were highly CIP-resistant (MIC geqslant R: gt-or-equal, slanted 4). Resistance by target modification was screened by PCR amplification and sequencing of the quinolone resistance determining regions (QRDRs) of gyrA and parC genes. Synergy experiments were also performed using ciprofloxacin and the proton-gradient dependent efflux pump inhibitor carbonyl-cyanide-m-chlorophenylhydrazone (CCCP), to check the contribution of efflux pumps. The presence of qnrA, qnrB and qnrS was also screened by PCR.

Results: All high-level CIP-resistant E. coli had two mutations in gyrA in combination with mutations in parC genes. Mutations in parC were only found in combination with gyrA mutations. The mutations found for gyrA were S83L, D87N and D87Y and for parC were S80R, S80I, E84V, E84K and E84G. 111 isolates had only the gyrA mutations. 17 isolates had double mutations both in gyrA and parC. 84 had double mutation in gyrA and a single mutation in parC. Contribution of efflux pump mechanisms was not detected in the isolates of the study. No qnrA or qnrB gene was detected, whereas 11 qnrS-positive E. coli isolates were found by sequencing of the amplicons to carry the qnrS1 allele. PFGE was performed in qnrS1 isolates that were found to belong in distinct genotypes.

Conclusions: Target mutation in QRDRs was the most prevalent mechanism of quinolone resistance in Greek CIP-resistant E. coli isolates. Transferable resistance by target protection or enzymatic modification was less common (9.6%). qnr genes seem to be common in ciprofloxacin-resistant clinical E. coli isolates and may contribute to the alarming rates of quinolone resistance in Greece.

Session Details

Date: 16/05/2009
Time: 00:00-00:00
Session name: 19th European Congress of Clinical Microbiology and Infectious Diseases
Location: Helsinki, Finland, 16 - 19 May 2009
Presentation type:
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