Dissemination of IncF group F1:A2:B20 plasmid-harbouring multidrug-resistant Escherichia coli ST131 before the acquisition of blaCTX-M in Japan

Objectives: The Escherichia coli O25-ST131 clone is responsible for global dissemination of the bla(CTX-M) gene. However, the prevalence of this clone in the digestive tract, devoid of antimicrobial selection, and its molecular epidemiology remain unclear. In this study, we examined the origin of bla(CTX-M)-positive E. coli O25-ST131 and its distribution. Methods: We separately sequenced the chromosomal and plasmid genomes of 50 E. coli O25 isolates obtained from faecal samples of patients with diarrhoea in Japan. Results: Although 36 (72%) of 50 E. coli O25 isolates were ST131, only 6 harboured bla(CTX-M). According to thefimH and ybbW sequences and fluoroquinolone susceptibility, H30R1 isolates were dominant (27/36; 75%) and possessed IncFll-FIA-FIB with FAB formula subtype F1:A2:620 plasmids at a high frequency (24/27; 89%). The F1:A2:620 plasmids possessed more resistance genes such as bla(TEM-1), aminoglycoside resistance genes and trimethoprim/sulfamethoxazole resistance genes compared with non-F1:A2:620 plasmids. In contrast, only one bla(CTX-M-14) gene was located on the F1:A2:620 plasmids, whereas the other three were located on IncEll (F4:A-:B-) (n =1) and IncZ (n = 2) plasmids. Two H30Rx-ST131 isolates harboured bla(CTX-M-15): one was on the chromosome and the other on the IncFIA-R plasmid. The stability and conjugation ability of the F1:A2:620 plasmids were compared with those of non-F1:A2:620 plasmids, which revealed higher stability but lower conjugative ability. Conclusions: These results suggest that E. coli H3OR1-ST131 is a multidrug-resistant clone containing several resistance genes in the F1:A2:620 plasmid, which were widely distributed before the acquisition of bla(CTX-M). (C) 2020 The Author(s). Published by Elsevier Ltd on behalf of International Society for Antimicrobial Chemotherapy.