Detection of plasmid mediated colistin resistance mcr-1 gene in ESBL producing Escherichia coli isolated from raw milk hard cheese in Egypt

The mcr-1 gene in 125 ESBL-producing Gram-negative bacteria obtained from animal products was screened and the location and transferability of the mcr-1 gene were examined. The mcr-1 gene was detected by PCR in one Escherichia coli isolate (RC263) obtained from hard cheese made from raw milk. Antimicrobial susceptibility test showed that the strain RC263 was phenotypically multidrug-resistant with colistin and nine other antimicrobials. Further genetic analysis indicated that this isolate also harboured the blaTEM and blaCTX-M-9 genes. S1-PFGE followed by Southern blotting verified that the mcr-1 gene was located on an approximately 153 kb plasmid. The plasmid was transferred to a recipient E. coli strain by conjugation, suggesting that the mcr-1 gene may spread to other Gram-negative bacteria. In conclusion, ESBL-producing E. coli carrying a transferable plasmid with mcr-1 gene was present in hard cheese in Egypt.