Emergence of CMY-2-Producing Escherichia coli in Korean Layer Parent Stock

The use of antimicrobials in food animals is the major determinant for the propagation of resistant bacteria in the animal reservoir. Especially, parent stock (PS) produces thousands of eggs for commercial laying hens and can transfer a variety of viral and bacterial agents to chicks. The objective of this study was to investigate the presence and distribution of third-generation cephalosporin-resistant and extended-spectrum β-lactamase (ESBL)- and plasmid-mediated AmpC (pAmpC)-producing Escherichia coli in the PS level of the layer operation system in Korea. A total of 591 E. coli isolates were tested in this study and resistance to the first-generation cephalosporins ranged from 60.0% to 71.1%, whereas the resistance to the second- and third-generation cephalosporins ranged from 18.3% to 28.9% and from 8.3% to 14.5%, respectively. Of the 65 third-generation cephalosporin-resistant E. coli isolates, 51 (78.5%) showed multidrug resistance and 18 (27.7%) exhibited phenotypic and genotypic characteristics of ESBL/pAmpC-producing E. coli. With regard to ESBL/pAmpC gene prevalence, only the CMY-2 gene was identified in all 18 ESBL/pAmpC-producing E. coli and two isolates possessed both the CMY-2 and TEM-1 genes. Pulsed-field gel electrophoresis (PFGE) analysis of the 18 CMY-2-producing E. coli isolates revealed four PFGE patterns from the same PS farm and flock and accorded both CMY-2 genes and antimicrobial resistance pattern. To the best of our knowledge, this is the first study to investigate the prevalence and characteristics of third-generation cephalosporin-resistant and CMY-2-producing E. coli isolated at the layer PS level; our findings support the critical need for a comprehensive surveillance program to monitor the emergence and dissemination of third-generation cephalosporin resistance.