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

ABSTRACTThree kinds of plasmid-mediated quinolone resistance (PMQR) determinants have been discovered and have been shown to be widely distributed among clinical isolates: qnrgenes, 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 β-lactamases (ESBLs) and AmpC β-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 μg/ml) isolates of the family Enterobacteriaceaewere selected from 36 companion animals and 65 food-producing animals in Guangdong Province, China, between November 2003 and April 2007, including 89 Escherichia coliisolates, 9 Klebsiella pneumoniaeisolates, and isolates of three other genera. A total of 68.3% (69/101) of the isolates produced ESBLs and/or AmpC β-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 qepAdetected alone or in combination in 8 (7.9%), 19 (18.8%), and 16 (15.8%) strains, respectively. The qnrgenes detected included one qnrB4gene, four qnrB6genes, and three qnrS1genes. Five strains were positive for both aac(6′)-Ib-crand qepA, while one strain was positive for qnrS1, aac(6′)-Ib-cr, and qepA. qnrB6was flanked by two copies of ISCR1with an intervening dfrgene downstream and sul1and qacEΔ1genes upstream. In another plasmid, aac(6′)-Ib-crfollowed intI1and arr-3was downstream. PMQR determinants are highly prevalent in ceftiofur-resistant Enterobacteriaceaestrains isolated from animals in China. This is the first report of the occurrence of PMQR determinants among isolates from companion animals.