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

Transmission of extended-spectrum β-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.