Prevalence Of mcr-1 Among Cefotaxime-Resistant Commensal Escherichia coli In Residents Of Vietnam

Purpose: The dissemination of colistin-resistant bacteria harboring the colistin-resistance gene mcr-1 in developing countries has recently entered the spotlight as an emerging public health threat, which is attributed to the abuse of colistin use in these countries. However, the prevalence of these bacteria in developing countries has not been extensively investigated. Therefore, in the present study, we examined the prevalence of cefotaxime-resistant commensal Escherichia coli harboring mcr-1 among residents of a representative Vietnamese village and assessed the characteristics of these isolates. Materials and methods: The stool samples, one stool sample per resident, of 612 residents were cultured on MacConkey agar with cefotaxime. Resulting E. coli-like colonies were isolated and examined further for the presence of colistin-resistant extended-spectrum beta-lactamase (ESBL)-producing E. coli with mcr-1. Antibiotic susceptibility tests were performed, and clonal relationship among colistin-resistant isolates was assessed. Results: Thirty-one of the 451 cefotaxime-resistant E. coli isolates were resistant to colistin and the majority possessed mcr-1, bla(CTX)(-M), and/or bla(TEM), except for two isolates that produced the AmpC beta-lactamase. All mcr-1 ESBL-producing E. coli isolates were multidrug-resistant (5-11 antibiotics). The isolates contained various plasmid replicon types, including the most prevalent types IncHI2 (54.8%), IncFIB (48.4%), and IncN (41.9%). In addition, 83.9% of the mcr-1 ESBL-E. coli isolates possessed a transposon ISApl1-mcr-1 segment. Furthermore, 77.4% of the mcr-1 ESBL-E. coli isolates belonged to phylogenetic group A. Pulsed-field gel electrophoresis analysis indicated limited clonal expansion of a specific strain. Conclusion: These results demonstrate the wide dissemination of colistin-resistant ESBL-E. coli harboring mcr-1 among commensal bacteria of rural residents in Vietnam, suggesting possible mobilization of the mcr-1 gene among ESBL-producing microbiota, which is a great public health concern.