ABSTRACT
Currently, few studies have investigated the mechanisms of resistance to colistin in Iran. The aim of this study was to investigate mcr-harbouring Escherichia coli dissemination in livestock and sewage in Iran. A total of 115 samples from cows (n = 38), chickens (n = 47) and urban sewage samples (n = 30) were collected. The presence of genes including mcr1-6 and ampC ß-lactamase (bla MOX, bla CIT, bla DHA, bla ACC, bla EBC, bla FOX) for colistin-resistant isolates was investigated by multiplex PCR method. Genetic association of colistin-resistant strains was also evaluated by ERIC PCR. Sixty-five isolates were identified as E. coli. Meaningless were resistant to colistin. The highest (26.1%) and lowest (3.07%) resistance were shown to ampicillin and meropenem respectively. Among the three colistin-resistant isolates, 2 (66%) were multidrug resistant, with one of them being mcr-1 positive and the other one positive for DHA ampC ß-lactamase gene. No mcr2-6 genes were found. Minimum inhibitory concentration of mcr-producing isolate was 4 mg/L by microbroth dilution. This study reports, first the detection of mcr-1 in E. coli from farm animals in Iran, a finding that is indicative of a global distribution of this plasmidic element and threatning the use of colistin as a last resort antibiotic. No clonal relationship was observed between the colistin-resistant E. coli isolates by ERIC-PCR. Monitoring the presence of these strains in animal sources help as to controlling the spread of resistance genes from animal to human is vital.