Plasmid-mediated quinolone resistance determinant qnrB19 in non-typhoidal Salmonella enterica strains isolated in Venezuela

Copyright © 2012 Gonzalez et al. This is an open-access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited Quinolone resistance in Enterobacteriaceae is typically mediated by chromosomal mutations leading to alterations in the target enzymes DNA gyrase and topoisomerase IV, or changes in drug entry and efflux. However, three plasmid-mediated quinolone resistance (PMQR) mechanisms conferring decreased susceptibility to quinolones (including some fluoroquinolones) have been recently described: QepA and OqxAB effluxes, Aac(6´)-Ib-cr aminoglycoside acetyltransferase and Qnr proteins (qnrA, qnrB, qnrC, qnrD and qnrS) [1,2]. Although plasmid-mediated quinolone resistance of Qnr type has been identified in Enterobacteriaceae from the United States, Europe, and Asia [1,2], little is known about the diversity, type or range of qnr genes in Latin America [3-6], especially in Venezuela. Therefore, the objective of this study was to screen for the presence of PMQR genes in non-typhoidal Salmonella enterica (NTS) strains with reduced susceptibility to fluoroquinolones, from clinical samples and chicken meat in Venezuela. A total of 127 NTS strains belonging to the collection of the Molecular Microbiology Laboratory of the Pharmacy Faculty of University of the Andes (Mérida, Venezuela), were enrolled in this study. These included 117 strains from stool specimens of pediatric patients collected from 2005 to 2007 and 10 isolates recovered from raw chicken meat in 2008. Six (4.7%) of these isolates showed a typical phenotype with reduced resistance to ciprofloxacin (MICs: 0.5 – 1 g/mL) and with affiliated susceptibility to nalidixic acid (MICs: 4-8 g/mL). These isolates were screened for extended-spectrum beta-lactamase (ESBL) phenotype, using cefotaxime and ceftazidime with and without clavulanic acid per Clinical and Laboratory Standards Institute (CLSI) guidelines [7] and confirmed by polymerase chain reaction (PCR) using specific primers for bla TEM , bla SHV and group bla CTX-M, [8]. Presence of qnrA, qnrB, qnrS, qnrD, aac(6´)-Ib and qepA genes was screened by multiplex and simplex PCR amplifications, using primers and conditions previously described [9,10]. In addition, mutations in quinolone resistance-determining regions (QRDR) of the gyrA, gyrB and parC genes were also determined [11]. Amplicons were sequenced to determine the gene variants and mutations. Regardless of origin and serovar, the qnrB gene was detected in six Salmonella strains. Sequence analysis of the amplification product revealed the qnrB19 variant (Table). No mutations were identified in the QRDR of the gyrA, gyrB and parC genes [11]. …