Diverse prevalence of 16S rRNA methylase genes armA and rmtB amongst clinical multidrug-resistant Escherichia coli and Klebsiella pneumoniae isolates

In this study, 112 Escherichia coli and 55 Klebsiella pneumoniae isolates with a multidrug-resistant (MDR) phenotype were collected from 2007 to 2009. All isolates simultaneously exhibited resistance to cefotaxime (or ceftazidime), ciprofloxacin (or levofloxacin) and amikacin. Plasmid-mediated 16S rRNA methylases, including armA, rmtA, rmtB, rmtC, rmtD, rmtE and npmA, were detected by polymerase chain reaction (PCR) amplification. Common β-lactamase genes, including blaTEM, blaSHV, blaCTX-M, blaPER, blaVEB, blaGES and blaOXA, as well as plasmid-mediated blaAmpC and plasmid-mediated quinolone resistance (PMQR) determinants, including qnrA, qnrB, qnrS, qepA and aac(6′)-Ib-cr, were also screened. The transferable capacity of resistance plasmids was established by conjugation testing. The genetic relatedness of isolates was analysed by pulsed-field gel electrophoresis (PFGE). Only armA and rmtB genes were detected in this study. Data showed that 93.8% of MDR E. coli and 94.5% of MDR K. pneumoniae carried at least one of armA or rmtB. The armA and rmtB genes were present in 11.6% and 82.1% of MDR E. coli, respectively. In parallel, 58.2% and 40.0% of MDR K. pneumoniae were armA- and rmtB-positive, respectively. Furthermore, the qepA gene was present in 66.3% of rmtB-carrying MDR E. coli, but it was rarely detected in MDR K. pneumoniae. Approximately 71.9% of armA-positive MDR K. pneumoniae simultaneously co-carried qnrB and blaDHA. Moreover, 78.1% and 63.6%, respectively, of armA-positive and rmtB-positive MDR K. pneumoniae strains harboured qnr alleles and 53.1% and 59.1% harboured aac(6′)-Ib-cr. In addition, MDR E. coli strains exhibited a low prevalence of qnr alleles and aac(6′)-Ib-cr. PFGE analysis revealed divergent genetic relatedness, suggesting horizontal dissemination of armA and rmtB along with common β-lactamases and PMQR determinants amongst clinical MDR E. coli and K. pneumoniae isolates.