PLASMID MEDIATED COLISTIN RESISTANCE IN ENTEROBACTERIACEAE ISOLATED FROM FECES OF BROILER CHICKEN IN THE UNITED ARAB EMIRATES

Although human infections with colistin-resistant Mcr-producing Enterobacteriaceae have been reported from the Arabian Peninsula, the presence of mcr gene in strains of animal origin has not been studied. Ten composite faecal samples were collected in each of four geographically distant poultry farms in Abu Dhabi Emirate. Ten colonies from McConkey agar containing 1 mg/L colistin from each sample were PCR-screened for mcr-1, mcr-2, MCR-3, mcr-4, mcr-5. Of the positive ones, one isolate representing each distinct plasmid profile was selected for susceptibility testing and for whole-genome sequencing (WGS). Transfer of the MCR-1 gene into Escherichia coli K12 was attempted. Plasmids were first compared by restriction fragment length polymorphism (RFLP). Representatives of plasmids with distinct RFLP profiles were sequenced and their incompatibility type was determined. MCR-1 positive colonies were identified in 36 of the 40 samples. The 40 isolates selected were resistant to ampicillin and colistin (MIC range 4-\u3e256 mg/L) with variable resistance to 3rd generation cephalosporins, tetracyclines, quinolones, cotrimoxazole and aminoglycosides. Thirty-five Escherichia coli, two Escherichia albertii, two Klebsiella pneumonia and one Salmonella Minnesota were identified based on their whole genomes. They represented a remarkable variety of sequence types and in the case of E. coli core genome multi-locus sequence types. Beyond MCR-1, all strains carried at least one beta-lactamase, and aminoglycoside, tetracycline, and co-trimoxazole resistance genes, seven of them ESBL genes and one blaCMY-2. Transfer of the MCR-plasmid was successful in the case of 6 IncHI2, 26 IncI2 and 4 IncX4 plasmids, respectively. Co-transfer of ampicillin, chloramphenicol, and tetracycline resistance with the MCR-1 gene was observed in the case of the IncHI2 plasmids. From the four chicken farms, multiple species of Enterobacteriaceae exhibiting a variety of MLST and cgMLST patterns, carrying the MCR-1 gene on plasmids of three different incompatibility types were isolated. Similar strains and similar plasmids were present in multiple farms. These data show that the farms are heavily infested with MCR-1 carrying strains with the possibility to transfer it, via the food chain, to humans