Acquisition of Plasmid-Mediated Colistin Resistance Gene <i>mcr-1</i> in <i>Escherichia coli</i> of Livestock Origin in Bangladesh

<b><i>Aims:</i></b> To investigate plasmid-borne colistin resistance mechanism (plasmid-mediated colistin resistance [<i>mcr-1</i>]) in <i>Escherichia coli</i> of human, veterinary, and environmental origin in Bangladesh. <b><i>Materials and methods:</i></b> A total of 810 samples were collected from different sources. Isolation and identification of <i>E. coli</i> was performed using classical bacteriology and then tested for antimicrobial susceptibility. Colistin-resistant isolates were further analyzed for <i>mcr-1</i> gene using PCR. Minimum inhibitory concentration (MIC) was determined using microbroth dilution technique. After sequencing of <i>mcr-1</i> gene, phylogenetics was conducted to see the relationship with other <i>mcr-1</i> gene sequences. <b><i>Results:</i></b> A total of 358 <i>E. coli</i> were isolated from 810 samples of humans, animals, environment, and food in Bangladesh. Of them 49 (15.9%) isolates were phenotypically resistant to colistin and 254 (70.9%) were resistant to multiple antimicrobials. <i>mcr-1</i> gene was detected in three <i>E. coli</i> isolates of poultry source. For the three <i>mcr-1</i> positive isolates the MIC of colistin sulfate was 4, 8, and 128 μg/mL. Gene sequencing of two of the three <i>mcr-1</i> positive isolates and phylogenetic analysis showed close similarities of one isolate to other <i>mcr-1</i> sequences available at GenBank while the other appeared to have evolved locally. <b><i>Conclusion:</i></b> First-ever report on circulation of <i>mcr-1 E. coli</i> of livestock origin in Bangladesh.