Multidrug Antimicrobial Resistance and Molecular Detection of mcr-1 Gene in Salmonella Species Isolated from Chicken

Abstract

Colistin (polymyxin E) is widely used in animal and human medicine and is increasingly used as one of the last-resort antibiotics against Gram-negative bacilli. Due to the increased use of colistin in treating infections caused by multidrug-resistant Gram-negative bacteria, resistance to this antibiotic ought to be monitored. The study was undertaken to elucidate the molecular mechanisms, genetic relationships and phenotype correlations of colistin-resistant isolates. Here, we report the detection of the <i>mcr-1</i> gene in chicken-associated <i>Salmonella</i> isolates in Bangladesh and its in-silico functional analysis. Out of 100 samples, 82 <i>Salmonella</i> spp. were isolated from chicken specimens (liver, intestine). Phenotypic disc diffusion and minimum inhibitory concentration (MIC) assay using different antimicrobial agents were performed. <i>Salmonella</i> isolates were characterized using PCR methods targeting genus-specific <i>invA</i> and <i>mcr-1</i> genes with validation for the functional analysis. The majority of the tested <i>Salmonella</i> isolates were found resistant to colistin (92.68%), ciprofloxacin (73.17%), tigecycline (62.20%) and trimethoprim/sulfamethoxazole (60.98%). When screened using PCR, five out of ten <i>Salmonella</i> isolates were found to carry the <i>mcr-1</i> gene. One isolate was confirmed for <i>Salmonella enterica</i> subsp. <i>enterica</i> serovar Enteritidis, and other four isolates were confirmed for <i>Salmonella enterica</i> subsp. <i>enterica</i> serovar Typhimurium. Sequencing and phylogenetic analysis revealed a divergent evolutionary relationship between the catalytic domain of <i>Neisseria meningitidis</i> lipooligosaccharide phosphoethanolamine transferase A (LptA) and MCR proteins, rendering them resistant to colistin. Three-dimensional homology structural analysis of MCR-1 proteins and molecular docking interactions suggested that MCR-1 and LptA share a similar substrate binding cavity, which could be validated for the functional analysis. The comprehensive molecular and in-silico analyses of the colistin resistance <i>mcr-1</i> gene of <i>Salmonella</i> spp. of chicken origin in the present study highlight the importance of continued monitoring and surveillance for antimicrobial resistance among pathogens in food chain animals.