Molecular characteristics of extended-spectrum and plasmid-mediated AmpC β-lactamase-producing Escherichia coli isolated from commercial layer in Korea

In the poultry industry, commercial layer farms play an important role in meeting the protein demand through the supply of eggs. However, the risk of contamination by beta-lactamase-producing Escherichia coli in eggs laid by commercial chickens is significant. In this study, we investigated the rate of extended-spectrum beta-lactamase (ESBL) and plasmid-mediated AmpC (pAmpC) beta-lactamase-producing E. coli isolated from layer hens and characterized their molecular background. Among the 92 cefotaxime-resistant E. coli isolates, 66 (71.7%) were identified as multidrug resistant and 29 showed phenotypic and genotypic characteristics of beta-lactamase-producing E. coli. The ESBL/pAmpC genes bla(CTX-M-1), bla(CTX)-(M-14),bla(CTX-M-15), and bla(CMY-2) were detected in 1, 6, 5, and 4 isolates, respectively. The non-ESBL/pAmpC gene bla(TEM-1) was found in 16 isolates. Three isolates harbored both bla(TEM-1)and bla(CTX-M-14) genes. A total of 12 isolates also carried class 1 integrons, with 3 different gene cassette arrangements found in 8 of these isolates. A pulsed-field gel electrophoresis (PFGE) analysis of the 29 beta-lactamaseproducing E. coli isolates revealed that 4 PFGE patterns were consistent with the beta-lactamase gene and layer farm origin, and showed a similar antibiotic resistance pattern. Our results suggest that comprehensive surveillance and more prudent use of third-generation cephalosporins in commercial layer farms is necessary to prevent the dissemination of ESBL/pAmpC-producing E. coli.