Edible river fish-derived extended-spectrum β-lactamase (ESBL)-producing Enterobacterales harboring transferable plasmids encoding blaCTX-M-15, blaCTX-M-27, and blaCTX-M-55

Transmission of extended-spectrum beta-lactamase (ESBL) genes has increased the global prevalence of ESBL- producing bacteria, especially in developing countries. Human infection with these bacteria may be food- mediated but has not been fully elucidated. Therefore, we aimed to examine ESBL-producing bacteria in edible river fish and elucidate their potential for horizontal gene transfer. A total of 173 ESBL-producing Enterobacterales were isolated (Escherichia coli [n =87], Klebsiella pneumoniae [n =52], Enterobacter cloacae complex [n =18], Citrobacter freundii complex [n =14], Atlantibacter hermannii [n =1] and Serratia fonticola [n =1]) from 56 of 80 fish intestinal contents sampled. Among the bacterial bla(CTX-M) genotypes, bla(CTX-M-55) was the most predominant, followed by bla(CTX-M-15), bla(CTX-M-27), and bla(CTX-M-65). Furthermore, we found that ESBL- producing Enterobacterales were able to transfer their bla(CTX-M) genes to E. coli. In summary, our results suggest that ESBL-producing Enterobacterales transfer bla(CTX-M) to indigenous gut E. coli in humans, following the consumption of contaminated fish.