Investigation of the presence of plasmid-mediated MCR gene regions in clinical E. Coli isolates and determination of close relationships of these genes

E. coli is one of the most commonly isolated gram-negative bacteria in hospital-acquired infections. In addition to being a member of the normal flora, it is also known for causing systemic infections. The main factor that makes these infections significant is the resistance developed by the bacteria to antibiotics commonly used in routine treatment. Colistin is one of the last-resort antibiotics used against gram-negative bacteria. Although its use is restricted due to nephrotoxicity and neurotoxicity, it has regained importance in recent times, especially with the emergence of strains that have developed multidrug resistance. However, the indiscriminate use of colistin has also led to the development of resistance to this antibiotic. Until now, it was believed that the colistin resistance was only due to mutations in intrinsic genes. However, with the discovery of mobile colistin resistance (mcr) genes, it was revealed that colistin resistance can be transferred between strains via plasmids. There are 10 different alleles of these genes. In our study, we aimed to investigate the presence of all mcr alleles identified on plasmids in order to determine the prevalence of plasmid-mediated resistance in our region and to explore the relationships between the detected genes. For this purpose, 26 clinical E. coli strains, isolated and consecutively selected from the Department of Medical Microbiology at Çukurova University Faculty of Medicine, were included in the study. Two of these isolates were resistant (%7.69) to colistin. After the 26 E. coli strains were confirmed using conventional methods, their colistin resistance profiles were validated by a broth microdilution test. Plasmids were isolated from the strains using a kit, and the presence of mcr gene regions was investigated by real-time PCR. The mcr-1 gene was detected in one resistant isolate, while no other mcr alleles were found in any of the isolates. As a result of the study, the ratio of mcr-1 positive isolates was found to be 3.8% (1/26), and the ratio among resistant strains was 50% (1/2). Due to the absence of any other mcr alleles besides mcr-1 in the isolates, the relationships between the genes could not be determined. The low prevelance of colistin resistance and the absence of mcr genes other than mcr-1 in the colistin-resistant isolate suggest that the risk of antibiotic resistance in our region is still low. Our study is also the first to examine all plasmid-mediated mcr alleles in E. coli isolates in our region.