Characteristics of the extended-spectrum-β-lactamase-producing Escherichia coli isolated from diseased livestock and poultry in Taiwan

A total of 297 Escherichia coli isolates from diseased livestock with diarrhea and 269 isolates from poultry affected by colibacillosis were assessed for extended-spectrum-β-lactamase (ESBL) production. In livestock, 36 isolates (12.1%) were ESBL-producing, with pigs (52.8%), cattle (30.5%), and goats (16.7%) being the most affected. Poultry exhibited 22 ESBL-producing strains (8.6%), with distribution among species: chicken (36.3%), duck (22.7%), goose (22.7%), and others (18.2%). ESBL-producing E. coli demonstrated higher drug resistance, except for amoxicillin/clavulanic acid, while all isolates were susceptible to imipenem. The bla_CTX-M-55 gene, from the bla_CTX-M-1 group, was prevalent in the ESBL-producing E. coli from livestock and poultry. Multilocus sequence typing (MLST) identified distinct sequence types (STs) for 58 ESBL-producing E. coli, except for ST162 and ST1196, detected in both sources. Livestock yielded one ST10 and two ST38 isolates, while poultry exhibited two ST69 and one ST617 isolates, recognized as common extraintestinal pathogenic E. coli (ExPEC) types. In conjugation assays, all ESBL-producing E. coli successfully transferred bla genes to the recipient E. coli J53 strain. The findings underscore food-producing animals as significant ESBL reservoirs, emphasizing the crucial role of judicious antimicrobial use on farms.