A survey of β-lactamase and 16S rRNA methylase genes among fluoroquinolone-resistant Escherichia coli isolates and their horizontal transmission in Shandong, China.

The prevalence of β-lactamase, 16S rRNA methylase genes, and plasmid-mediated fluoroquinolone-resistance (PMQR) determinants (qnrC and qnrD) was determined by polymerase chain reaction in fluoroquinolone-resistant Escherichia coli isolated from a chicken farm, a pig farm, and a hospital in Shandong, China in 2007. The bla(TEM) and bla(CTX-M) were the most prevalent β-lactamase genes in isolates from chickens (88.4%, 175/198 and 81.3%, 161/198) and hospitalized patients (87.8%, 122/139 and 69.1%, 96/139). The bla(TEM) was the most prevalent β-lactamase gene observed in isolates from pigs (98.5%, 135/137). The gene bla(CMY-2) was also predominant among isolates from chickens (20.2%, 40/198). The bla(LAP-1) gene was first detected in one strain from chickens and humans (pig farm workers) in China. Only one strain from hospitalized patients was found to possess bla(SHV). The rmtB was the most prevalent 16S rRNA methylase gene detected in isolates from chickens (19.7%, 39/198) and hospitalized patients (15.8%, 22/139). To our knowledge, this is the first report of the detection of the qnrD gene in E. coli from chickens and pigs in China. The qnrC and bla(KPC) genes were not detected in any of the isolates. Results of southern hybridization revealed that PMQR determinants, β-lactamases, and 16S rRNA methylase genes were located on the same plasmid in E. coli strains derived from patients. Also, PMQR determinants and β-lactamase genes were localized on the same plasmid in an E. coli strain of animal origin. Results of conjugation experiments revealed that all of these plasmid-based resistance genes can be transferred by conjugation through horizontal transmission.