The Emergence of CTX-M-55 in Extended-Sectrum β-Lactamase-Producing Escherichia coli from Vegetables Sold in Local Markets of Northern Thailand.

Extended-spectrum β-lactamase (ESBL)-producing Escherichia coli is spreading worldwide and poses a public health issue. Assessing their presence in the environment and food chain products would elucidate the pathway of their foodborne transmission. Here, we investigated the prevalence of ESBL-producing E. coli in fresh vegetables purchased from fresh markets in Chiang Rai, Thailand. Overall, 8.8% of the samples collected contained ESBL-producing E. coli, of which 81.3% were multidrug-resistant. All isolates carried blaCTX-M-55, and 10 isolates contained ISEcp1. One E. coli strain harbored blaCTX-M-55 co-occurring with blaTEM-1. Furthermore, 13 different sequence types (ST48, ST101, ST155, ST165, ST398, ST414, ST457, ST515, ST542, ST1081, ST3045, ST7538, and ST10651) were identified. One E. coli strain belonged to ST101, which is prevalent among human isolates. Thus, our study demonstrated the spread of CTX-M-55 on non-ST131 vegetable isolates that are not global pandemic strains and suggests that they may be a source of antibiotic resistance gene transfer from agricultural foods to humans. Further studies are needed to investigate whether the ESBL-producing E. coli transfer resistance genes to commensal E. coli and cause severe disease.