The prevalence of plasmid-mediated quinolone resistance (PMQR) determinants (qnrA,
qnrB, qnrS, aac(6')-Ib-cr, and qepA) was investigated in a collection of 47 extended-spectrum
β-lactamase (ESBL) producing enterobacterial isolates with reduced susceptibility
to fluoroquinolones, recovered at Nantes University hospital, in 2006. qnr, aac(6')-Ib-cr,
and qepA genes were screened by PCR, and positive results were subsequently confirmed
by sequencing. The epidemiological relationship between positive isolates was studied
by pulsed-field gel electrophoresis (PFGE). qnr-positive isolates were analyzed for
antimicrobial susceptibility and presence of mutations in the quinolone resistance-determining
region (QRDR) of gyrA and parC genes. ESBL genes were characterized by PCR and sequencing.
Conjugation experiments were performed to determine whether the qnr-carrying plasmids
were self-transferable. Two Klebsiella pneumoniae isolates (4.3%), not clonally related,
harboured a qnrS1 gene, whereas no qnrA- or qnrB-positive isolate was detected. The
aac(6')-Ib-cr gene was detected in 11 Escherichia coli and one K. pneumoniae isolates.
None of the 47 isolates carried the qepA gene. ESBLs associated with QnrS1 were CTX-M-14
and CTX-M-15. The CTX-M-15 producing isolate was highly resistant to fluoroquinolones
and harboured three mutations in the QRDR and two PMQR determinants (qnrS1 and aac(6')-Ib-cr).
The CTX-M-14-producing isolate exhibited reduced susceptibility or resistance to fluoroquinolones
without resistance to nalidixic acid. This strain harboured only a qnr gene on a single
170 kb transferable plasmid, without any mutation in the QRDR. In conclusion, our
study showed that aac(6')-Ib-cr gene had occurred in multiclonal ESBL-producing enterobacterial
isolates collected at Nantes University hospital in 2006, with a higher prevalence
than qnr genes.
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