Predominance of blaCTX-M-65 and blaCTX-M-55 in extended-spectrum β-lactamase-producing Escherichia coli from raw retail chicken in South Korea

Objectives: Extended-spectrum beta-lactamase-producing Escherichia coli (ESBL-EC) are a serious public health concern worldwide. The aim of this study was to characterise ESBL-EC isolated from raw retail chicken in South Korea. Methods: The antimicrobial resistance, phylogenetic group and virulence gene prevalence of 67 ESBL-EC isolated from retail chicken in South Korea were investigated. Results: All of the isolates possessed bla(CTX-M) genes, predominantly bla(CTX-M-65) (52.2%) and bla(CTX-M-55) (25.4%), and three isolates harboured both bla(CTX-M-65) and bla(CTX-M-55). More than one-half of the ESBL-EC strains also carried bla(TEM). Antimicrobial susceptibility testing revealed that 98.5% of the strains were multidrug-resistant (MDR). Phylogenetic analysis showed that group A was predominant (56.7%), followed by B1 (19.4%), E (8.9%), B2 (6.0%) and D (6.0%). Virulence genes associated with extraintestinal pathogenic E. coli (ExPEC) were frequently detected in isolates of phylogenetic groups B1, B2, D and E. Conclusion: The results in this study demonstrate that retail chicken in South Korea is highly contaminated with MDR ESBL-EC and may serve as a reservoir for transmitting ExPEC to humans. (C) 2019 The Authors. Published by Elsevier Ltd on behalf of International Society for Chemotherapy of Infection and Cancer.