Occurrence of plasmid-mediated quinolone resistance among bacteria isolated in animals in Portugal

Background: Plasmid-mediated quinolone resistance (PMQR) is increasingly identified worldwide in Enterobacteriaceae. The aim of this study was to evaluate the extension of PMQR in isolates from animals in Portugal. Methods: We screened 186 Enterobacteriaceae isolates for the presence of PMQR determinants, identified at National Laboratory of Veterinary Research (2008-2009). A total of 92 Salmonella isolates were isolated from broilers, layers and pigs, and 94 Escherichia coli were from farm animals, birds and mammals. Susceptibility testing of all isolates was performed by disk diffusion method, and MICs against nalidixic acid, ciprofloxacin, gatifloxacin, levofloxacin, ofloxacin, enrofloxacin, morbifloxacin and norfloxacin were determined by E-test for PMQR-positive isolates. PCR and nucleotide sequencing, by using specific primers, were used to screen for the presence of PMQR-encoding genes. The genetic context of PMQR genes was evaluated by using different molecular methods. Results: We identified 5 qnrC-positive isolates: 2 Salmonella enteritidis collected in 2 layer chicken and in 3 E. coli from 2 broilers and one pig; 3 qnrS1 genes were detected in E. coli isolates from a broiler (co-expressing a qnr-C gene), a dog and a turtle-dove. The aac-(6’)-Ib-cr gene was detected in an E. coli isolated from a mammalian. Seven PMQR-positive isolates showed diminished susceptibility to at least one quinolone, and one was detected in the range of susceptibility against the seven (fluoro)quinolones tested. Three E. coli and one S. enteritidis were PMQR- and TEM-1 and/or CTX-M-15-producing isolates. An E. coli with qnrC, qnrS1, and blaTEM-1 genes and an E. coli with qnrC gene were positive for genes coding to class 1 integrons. Conclusions: This survey showed that PMQR determinants are present in animals from different environments in Portugal, including food-producing animals, with a high frequency (3%) of QnrC-producing isolates. Susceptibility results demonstrate the difficulty to predict the PMQR mechanisms by phenotypic methods. Overall, the study suggests that PMQR genes are undergoing a dissemination process, which needs surveillance.