Prevalence of β-Lactamase and 16S rRNA Methylase Genes Among Clinical Escherichia coli Isolates Carrying Plasmid-Mediated Quinolone Resistance Genes from Animals

Plasmid-mediated quinolone-resistance (PMQR) genes were determined by polymerase chain reactions (PCRs) in 250 Escherichia coli isolates from food-producing animals in Guangdong, China, in 2009-2010. Then, the prevalence of plasmid-mediated beta-lactamase and 16S rRNA methylase genes was determined by PCRs among the PMQR-positive isolates. One hundred fifty-seven (62.8%) isolates were found to harbor at least one PMQR gene, and qnrS (84) and oqxAB (97) were the most two prevalent PMQR genes. beta-lactamase (ESBL and/or AmpC type) genes were detected in 106 of the 157 PMQR-positive strains. The bla(TEM-1) (78) was the most prevalent beta-lactamase gene in the 157 PMQR-positive isolates, followed by bla(CMY-2) (28), bla(CTX-M) (25), bla(SHV-1) (3), and bla(DHA-1) (3). Twenty-nine were detected to produce more than one type of beta-lactamase. The rmtB was the most prevalent 16S rRNA methylase gene detected (11.5%, 18/157), and armA was detected in only two (1.27%, 2/157) isolates, with one isolate coharboring rmtB and armA. Sixteen isolates were found to coharbor the three types of resistance genes detected in this study. Only 1 transconjugant JGDA2 harboring oqxAB, aac(6')-Ib-cr, bla(DHA-1), and rmtB was obtained from the 16 isolates harboring the three types of resistance genes, by conjugation experiment. The results of Southern blot hybridization revealed that oqxAB, bla(DHA-1), and rmtB were colocated on the same plasmid of similar to 54 kb in the JGDA2. To our knowledge, this is the first description of the coexistence of the oqxAB, rmtB, and bla(DHA-1) resistance genes on the same plasmid in one E. coli strain.