Potential transmission opportunity of CTX-M-producing Escherichia coli on a large-scale chicken farm in Vietnam

•ESBL-producing Escherichia coli were detected in 83.3% of Vietnamese chicken farm workers.•The rate of ESBL-producing E. coli in a chicken farm was higher than in the community.•Clonal distribution of ESBL-producing E. coli was observed only on the chicken farm. Extended-spectrum β-lactamase (ESBL)-producing Escherichia coli have disseminated worldwide. This study investigated blaCTX-M-positive E. coli on a large-scale Vietnamese chicken farm and analysed whether there was any difference in prevalence and molecular characteristics of blaCTX-M-positive E. coli between the farm and the Vietnamese community. Faecal samples were collected from 24 human individuals and 38 chickens from the large-scale chicken farm as well as 51 humans and 36 chickens from the community. All samples were collected between June 2013 and June 2014 in Bavi Province in the Red River Delta region of Vietnam. Molecular characterisation of CTX-M-producing E. coli and genetic relatedness among the isolates were evaluated by conventional typing methods. Antimicrobial susceptibility of the isolates was evaluated by the disk diffusion method. The prevalence of blaCTX-M-positive E. coli was 83.3%, 71.1%, 54.9% and 13.9% in farm workers, farm chickens, community individuals and community backyard chickens, respectively. On average, blaCTX-M-positive E. coli isolates from farm chickens were resistant to 8.3 different antibiotics. The average number of detected aminoglycoside-modifying enzyme genes (3.4 genes) and the detection rate of the plasmid-mediated colistin resistance gene mcr-1 (33.3%) were higher in blaCTX-M-positive E. coli isolated from farm chickens compared with other sampling groups. In addition, two types of indistinguishable pulsed-field gel electrophoresis (PFGE) patterns were observed in six blaCTX-M-65-positive E. coli and three blaCTX-M-55-positive E. coli from farm chickens. These results suggest a more frequent transmission opportunity of blaCTX-M-positive E. coli on the large-scale Vietnamese chicken farm.