Investigation of Phenotypic and mcr-1-Mediated Colistin Resistance in Escherichia coli

This study aimed to investigate colistin resistance in Escherichia coli isolated from a total of 166 stool samples that were obtained from chickens shipped to slaughter in Turkey and the presence of the mcr-1 gene, which has been recently discovered and is one of many genes causing plasmid-mediated colistin resistance. To this end, 200 E. coli isolates were collected and identified from feces obtained from intestinal samples of the broiler chickens included in this study. To reveal the phenotypic colistin resistance profile, the minimum inhibitory concentration of colistin for each isolate was determined using the cation-adjusted broth microdilution method. Phenotypic colistin resistance was observed in 15 (7.5%) out of 200 E. coli samples obtained from 7 different poultry slaughterhouses. The presence of the mcr-1 gene, which provides plasmid-mediated colistin resistance, was investigated by the polymerase chain reaction method to detect genotypic colistin resistance. The mcr-1 gene was not detected in any of the studied samples, including isolates that exhibited phenotypic colistin resistance. The absence of the plasmid-mediated mcr-1 gene, although colistin resistance was detected, suggested that the resistance was of chromosome origin or that there were other genes responsible for resistance. However, it is thought that it is necessary to conduct new studies that will investigate the newly emerging plasmid-mediated genes in the future