Prevalence and Characterization of Plasmid-Mediated Quinolone Resistance Genes in Extended-Spectrum β-Lactamase–Producing Enterobacteriaceae Isolates in Mexico

The objectives of this study were to investigate the prevalence of plasmid-mediated quinolone resistance genes in a collection of 226 extended-spectrum β-lactamase (ESBL)–producing Enterobacteriaceae isolates and characterize the qnr -positive isolates. The rate of qnr -positive isolates was 21.6% (49/226), 49.5% for aac(6′)-Ib-cr (112/226), and 1.7% for qepA1 (4/226). Those isolates carried qnr genes corresponding to types qnrB (71.4%), qnrS1 (24.4%), and qnrA1 (18.3%). The distribution among bacterial species was as follows: 55.8% (19/34) to Enterobacter cloacae , 50% (28/56) to Klebsiella pneumoniae , and 1.4% (2/136) to Escherichia coli . The characterization of qnr -positive isolates indicated the ESBL SHV-types as the most prevalent (81.6%), including the ESBLs SHV-12, SHV-5, and SHV-2a, followed by CTX-M-15 (44.9%) and TLA-1 (8.1%). In addition, for qnr -positive isolates, the prevalence of aac(6′)-Ib-cr was 55.1%, but qepA was not identified. Alterations at codons Ser-83 and Asp-87 in GyrA and at codons Ser-80 in ParC were observed in 69% and 80% of the qnr -positive isolates, respectively. The analysis of the transconjugants revealed a cotransmission of bla CTX-M-15 with qepA1 or aac(6′)-Ib-cr and/or qnrA1 and bla SHV-type with qnrB5 and qnrB6 genes. To conclude, these findings indicate a high prevalence of qnr and aac(6′)-Ib-cr among ESBL-producing isolates from Mexican hospitals and point to the wide spread of qnr -like determinants associated to ESBLs SHV- and CTX-M-type in Mexican clinical isolates.