Occurrence and genetic characteristics of mcr-1-positive colistin-resistant E. coli from poultry environments in Bangladesh

Abstract

Colistin is one of the last-resort antibiotics for the treatment of multidrug-resistant (MDR) Gram-negative bacterial infections. We determined the occurrence and characteristics of mcr-1-producing Escherichia coli obtained from live bird markets (LBMs), rural poultry farms (RPFs) and rural household backyard poultry environments (HBPs) in Bangladesh. We tested 104 extended-spectrum β-lactamase (ESBL)-producing E. coli isolated during 2017–2018 from poultry sources for colistin resistance. We analysed the resistant isolates for the mcr genes and characterized mcr-positive isolates for antibiotic susceptibility, antibiotic resistance genes, transmissible plasmids and clonal diversity. Of 104 isolates, 98 (94%) had MICcolistin ≥4 μg/mL and 14 (13.5%) were positive for mcr-1, of which 10 were from LBMs (n = 10), 3 were from RPFs and 1 was from an HBP. All 14 mcr-1 E. coli were resistant to third-generation cephalosporin and tetracycline, whereas 12 were resistant to fluoroquinolone and sulfamethoxazole, 10 were resistant to aminoglycosides and 3 were resistant to nitrofurantoin. Four isolates carried conjugative mcr-1 plasmid of 23–55 MDa in size. The 55 MDa plasmid found in two isolates carried additional resistant genes including blaCTX-M-group-1 and blaTEM-1 (ESBL), qnrB (fluoroquinolone), and rmtB (aminoglycoside). These plasmids belong to the IncF family with additional replicons: HI1 and N. Enterobacterial repetitive intergenic consensus-polymerase chain reaction revealed a heterogeneous banding pattern of mcr-1-positive isolates. We report a 13.5% prevalence of mcr-1-positive MDR E. coli in poultry faecal samples predominantly from LBMs in Bangladesh accentuating the need for safe disposal of poultry faeces and hygiene practices among people exposed to poultry.

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