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 β-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. β-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 β-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 β-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 ∼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.