Phenotypic characterization of the resistance of Salmonella – Shigella isolates to colistin and detection of mcr1/2 genes

Objective: Colistin is one of the latest line of therapeutics used in the management of infections due to multiresistant Gram-negative bacteria. The current emergence of colistin resistance, in particular through the mediation of plasmid resistance genes (mcr1 and mcr2) in intestinal bacteria is a worldwide concern. The objective of this study is to evaluate the sensitivity of Salmonella and Shigella strains to colistin and the detection of mcr1 and mcr2 genes within these strains. Methodology and Results: The colistin sensitivity profile of 30 Salmonella strains and 5 Shigella strains was determined using the Minimum Inhibitory Concentrations in liquid medium of Mueller Hinton and the results were interpreted in accordance with the standards of the European Committee on Antimicrobial Susceptibility Testing Epidemiological cut-off 2020 version 10.0. Finally, the mcr1 and mcr2 genes were detected by a conventional PCR. Overall, a phenotypic resistance rate of 20% was recorded for Salmonella-Shigella pathogens, with a frequency of 17.1% for Salmonella and 2.9% for Shigella. Molecular screening of these isolates revealed a lack of detection of the mcr1 and mcr2 genes in their genetic heritage. Conclusion and application of results: this study shows that Salmonella and Shigella strains are resistant to colistin, however the mcr 1 and 2 genes have not been amplified. To this end, the rational use of colistin must be applied in the human and animal field in order to curb the increase and spread of resistance to this molecule. Keywords: Colistin, Gabon, mcr, resistance, Salmonella-Shigella