Antimicrobial Resistance Profiles and Molecular Characteristics of Extended-Spectrum-Lactamase-ProducingSerovar Typhimurium Isolates from Food Animals During 2010-2021 in South Korea.

Abstract

Extended-spectrum-lactamase (ESBL)-producingis emerging as a worldwide public health concern. In this study, we aimed to investigate the antimicrobial resistance profiles and molecular characteristics of ESBL-producingserovar Typhimurium (Typhimurium). We obtained a total of 995Typhimurium isolates from the feces and carcasses of pigs (= 678), chickens (= 202), and cattle (= 115) during 2010-2021 in Korea. We found that 35Typhimurium isolates (3.5%) showed resistance to ceftiofur: pigs (51.4%, 18/35) and cattle (42.9%, 15/35). All of the ceftiofur-resistantTyphimurium isolates demonstrated multidrug resistance. Moreover, ceftiofur-resistantTyphimurium isolates displayed significantly higher rates of resistance to chloramphenicol and trimethoprim/sulfamethoxazole than ceftiofur-susceptibleTyphimurium isolates (< 0.05). The ceftiofur-resistantTyphimurium isolates produced four different CTX-M-type-lactamase, comprisingin the majority (51.4%, 18/35), followed by(28.6%, 10/35),(17.1%, 6/35), and(2.9%, 1/35). Among the 35 ceftiofur-resistantTyphimurium isolates, 16-positive isolates and one-positive isolate were transferred to recipientRG488 by conjugation. The predominantly found transposable units were-(45.7%, 16/35), followed by-IS(28.6%, 10/35) and-IS(17.1%, 6/35). Ceftiofur-resistantTyphimurium represented 19 types, with types P1-19 (22.9%, 8/35) and P12-34 (22.9%, 8/35) making up the majority and being found in most farms nationwide. Sequence types (STs) were different by animal species: ST19 (48.6%, 17/35) and ST34 (42.9%, 15/35) were mostly found STs in pigs and cattle, respectively. These findings showed that food animals, especially pigs and cattle, act as reservoirs of-harboringTyphimurium that can potentially be spread to humans.