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

Colistin is one of the last-resort antibiotics for treatment of multi-drug resistant (MDR) Gram negative bacterial infections. We determined occurrence and characteristics of mcr-1-producing E. coli obtained from live bird markets (LBM), rural poultry farms (RPF) and rural household backyard poultry (HBP) in Bangladesh.

We tested 104 extended-spectrum β-lactamase (ESBL)-producing E. coli isolated during 2017-2018 from poultry sources for colistin resistance. We analyzed the resistant isolates for mcr gene 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 LBM (n = 10), 3 from RFP and 1 from HBP. All 14 mcr-1 E. coli were resistant to third generation cephalosporin and tetracycline, while 12 were resistant to fluoroquinolone and sulphamethoxazole, 10 were to aminoglycosides and 3 were to nitrofurantoin. Four isolates carried conjugative mcr-1 plasmid of 23 to 55 MDa in size. The 55 MDa plasmid found in 2 isolates carried additional resistant genes including blaCTX-M-group-1 and blaTEM-1 (ESBL), qnrB (fluoroquinolone) and rmtB (aminoglycoside). These plasmids belong to IncF family with additional replicons: HI1 and N. ERIC-PCR 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 fecal samples predominantly from LBMs in Bangladesh accentuating the need for safe disposal of poultry feces and hygiene practices among people exposed to poultry.