High Prevalence of Plasmid-Mediated Quinolone Resistance Determinants qnr, aac(6′)-Ib-cr, and qepA among Ceftiofur-Resistant Enterobacteriaceae Isolates from Companion and Food-Producing Animals

Three kinds of plasmid-mediated quinolone resistance (PMQR) determinants have been discovered and have been shown to be widely distributed among clinical isolates: qnr genes, aac(6')-Ib-cr, and qepA. Few data on the prevalence of these determinants in strains from animals are available. The presence of PMQR genes in isolates from animals was determined by PCR amplification and DNA sequencing. The production of extended-spectrum beta-lactamases (ESBLs) and AmpC beta-lactamases in the strains was detected, and their genotypes were determined. The genetic environment of PMQR determinants in selected plasmids was analyzed. All samples of ceftiofur-resistant (MICs >= 8 mu g/ml) isolates of the family Enterobacteriaceae were selected from 36 companion animals and 65 food-producing animals in Guangdong Province, China, between November 2003 and April 2007, including 89 Escherichia coli isolates, 9 Klebsiella pneumoniae isolates, and isolates of three other genera. A total of 68.3% (69/101) of the isolates produced ESBLs and/or AmpC beta-lactamases, mainly those of the CTX-M and CMY types. Of the 101 strains, PMQR determinants were present in 35 (34.7%) isolates, with qnr, aac(6')-Ib-cr, and qepA detected alone or in combination in 8 (7.9%), 19 (18.8%), and 16 (15.8%) strains, respectively. The qnr genes detected included one qnrB4 gene, four qnrB6 genes, and three qnrS1 genes. Five strains were positive for both aac(6')-Ib-cr and qepA, while one strain was positive for qnrS1, aac(6')-Ib-cr, and qepA. qnrB6 was flanked by two copies of ISCR1 with an intervening dfr gene downstream and sul1 and qacE Delta 1 genes upstream. In another plasmid, aac(6')-Ib-cr followed intI1 and arr-3 was downstream. PMQR determinants are highly prevalent in ceftiofur-resistant Enterobacteriaceae strains isolated from animals in China. This is the first report of the occurrence of PMQR determinants among isolates from companion animals.