Distribution and characteristics of extended spectrum β‑lactamase-producing Escherichia coli in stages of integrated broiler production in Korea.

Extended-spectrum β-lactamase (ESBL)-producing Escherichia coli (E. coli) are a major public health concern owing to their multidrug resistance and potential for transmission through the food chain. The broiler industry is operated as a vertically integrated system; therefore, the ESBL-producing E. coli can easily disseminate across production stages. The objective of this study was to provide the distribution and characteristics of ESBL-producing E. coli in each production stage of three integrated broiler operations in Korea, from breeder hatcheries to commercial broiler farms. The prevalence of ESBL-producing E. coli isolates was significantly highest in commercial broiler hatcheries (36.8 %-38.1 %), followed by broiler breeder farms (15.4 %-26.9 %), commercial broiler farms (2.8 %-18.2 %), and breeder hatcheries (9.8 %-12.8 %) (p < 0.05). Moreover, ESBL-producing E. coli isolates exhibited higher MIC50 values ranging from 16 to >512 μg/mL against 3rd- or 4th-generation cephalosporins, higher multidrug resistance prevalence (94.6 %-100 %) and co-resistance to more antimicrobial classes than non-ESBL-producing E. coli isolates at all stages of broiler production. The most prevalent ESBL gene was blaCTX-M-55 (80.0 %-100.0 %) by production stages of integrated broiler operations (p < 0.05), and class I integrons were detected in 25.5 %-33.3 % of isolates, but only 10 (6.2 %) isolates harbored gene cassettes. Phylogenetic group B1 (59.4 %-65.5 %) was the most significantly prevalent, and combination of IncFIB and IncFII plasmids (46.4 %-53.6 %) were the most common replicon types across production stages (p < 0.05). Moreover, a total of 136 (81.2 %-90.0 %) isolates showed transferability of ESBL genes, and most (91.9 %-100.0 %) of ESBL-producing E. coli isolates form biofilm. However, weak biofilm producers (54.5 %-71.0 %) were significantly prevalent than moderate or strong producers (p < 0.05). These findings support that it is necessary to establish stringent strategies for the use of ceftiofur, 3rd-generation cephalosporin, in broiler production in Korea, as demonstrated in Japan and Canada, where the prevalence of ESBL-producing E. coli decreased after the cessation of ceftiofur use in hatcheries.