Prevalence of plasmid-mediated quinolone resistance determinants qnr and aac(6 ′ )-Ib-cr in Escherichia coli and Klebsiella pneumoniae producing extended-spectrum β-lactamases in Spain

The presence of the plasmid-mediated quinolone resistance determinants qnrA, qnrB, qnrS and aac(6′)-Ib-cr was evaluated in a collection of 382 isolates of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli and Klebsiella pneumoniae collected between February and March 2006 for the nationwide Spanish GEIH-ESBL 2006 project. In total, 14 isolates (3.7%) were positive for qnr genes (3 qnrA1, 5 qnrB-like and 6 qnrS1) and 62 isolates (16.2%) were positive for the mutant variant of aac(6′)-Ib-cr. The Aac(6′)-Ib-cr enzyme was the most prevalent plasmid-mediated mechanism of quinolone resistance in Spain. Most of the Aac(6′)-Ib-cr-producing E. coli isolates (94.2%) carried two mutations in gyrA and two in parC, whilst only 57.2% of K. pneumoniae harbouring this enzyme were gyrA and/or parC mutants. Most qnr plasmids were transferable, but only four were conjugative. Plasmid incompatibility groups were identified for only four plasmids, belonging to FIA, HI2 and I1γ. The most prevalent ESBLs associated with qnr plasmids belonged to the SHV and CTX-M families. The present study highlights the broad geographical spread of qnr-like determinants in Spain and their association with the SHV-12 and CTX-M-9 ESBLs in human clinical isolates.