Isolation of mobile colistin-resistance (mcr) gene-harboring Escherichia coli from chicken droppings in Dhaka

Abstract

The use of antibiotics in poultry industries across the low and middle-income countries is increasing rapidly, contributing to emergence of resistance against the last line of drug like colistin causing public health threat. Therefore, this study aimed to investigate the prevalence of Mobile Colistin Resistance (mcr) genes in E. coli isolated from the fecal samples of broiler chickens in Dhaka city. A total of 50 fecal samples were collected from food markets and residential areas of Dhaka city. The samples were processed and streaked onto selective media to presumptively isolate E. coli. The isolates were further confirmed by polymerase chain reaction (PCR) analysis, targeting 16s rRNA regions. Detection of mcr genes was performed by employing multiplex PCR of mcr-1 to mcr-5 and mcr-6 to mcr-9, while mcr-10 gene was amplified by singleplex standard PCR. Lastly, phenotypic expression was assessed by the broth microdilution method (BMD) to determine the minimum inhibitory concentration (MIC). A total of 47 E. coli isolates were presumptively isolated from selective media and subsequently 41 confirmed by PCR followed by plasmid-mediated detection of mcr resistance genes. Among E. coli isolates, 3 carried mcr-1 (7.3%), 33 mcr-3 (80.5%), 12 mcr-6 (29.3%), 2 mcr-7 (4.9%) 28 mcr-8 (68.3%) and 1 mcr-9 (2.4%), mcr-2, mcr-4, and mcr-10 were not detected in any of the isolates of E. coli. Phenotypic susceptibility testing of the isolates were carried out by using BMD method, revealing that most of the isolates harboring mcr genes are resistant to colistin at MIC up to 4 ug/mL. The high prevalence of various mcr genes, notably mcr-3 and mcr-8, indicated that colistin resistance had been extensively disseminated in bacteria from chickens. Such findings indicate industrial poultry chicken as a potential source of multidrug-resistant pathogens. 5