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

Extended-spectrum -lactamase (ESBL)-producing is emerging as a worldwide public health concern. In this study, we aimed to investigate the antimicrobial resistance profiles and molecular characteristics of ESBL-producing serovar Typhimurium ( Typhimurium). We obtained a total of 995 Typhimurium isolates from the feces and carcasses of pigs ( = 678), chickens ( = 202), and cattle ( = 115) during 2010-2021 in Korea. We found that 35 Typhimurium isolates (3.5%) showed resistance to ceftiofur: pigs (51.4%, 18/35) and cattle (42.9%, 15/35). All of the ceftiofur-resistant Typhimurium isolates demonstrated multidrug resistance. Moreover, ceftiofur-resistant Typhimurium isolates displayed significantly higher rates of resistance to chloramphenicol and trimethoprim/sulfamethoxazole than ceftiofur-susceptible Typhimurium isolates ( < 0.05). The ceftiofur-resistant Typhimurium isolates produced four different CTX-M-type -lactamase, comprising in 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-resistant Typhimurium isolates, 16 -positive isolates and one -positive isolate were transferred to recipient RG488 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-resistant Typhimurium 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 -harboring Typhimurium that can potentially be spread to humans.