Profiling of antimicrobial resistance and plasmid replicon types in beta-lactamase producing Escherichia coli isolated from Korean beef cattle

ABSTRACT

In this study, 78 isolates of Escherichia coli isolated from Korean beef cattle farms were investigated for the production of extended-spectrum beta-lactamase (ESBL) and/or AmpC beta-lactamase. In the disc diffusion test with ampicillin, amoxicillin, cephalothin, ceftiofur, cefotaxime, ceftazidime, and cefoxitin, 38.5% of the isolates showed resistance to all of ampicillin, amoxicillin, and cephalothin. The double disc synergy method revealed that none of the isolates produced ESBL or AmpC beta-lactamases. DNA sequencing showed that all isolates encoded genes for TEM-1-type beta-lactamase. Moreover, 78.2% of the isolates transferred the TEM-1-type beta-lactamase gene via conjugation. In plasmid replicon typing of all donors, IncFIB and IncFIA were identified in 71.4% and 41.0% of plasmids, respectively. In transconjugants, IncFIB and IncFIA were the most frequent types detected (61.5% and 41.0%, respectively). Overall, the present study indicates that selection pressures of antimicrobials on beta-lactamases in beef cattle may be low relative to other livestock animals in Korea. Moreover, to reduce selection pressure and dissemination of beta-lactamase, the long-term surveillance of antimicrobial use in domestic beef cattle should be established.