The first report of the mobile colistin resistance gene, mcr-10.1, in Kenya and a novel mutation in the phoQ gene (S244T) in a colistin-resistant Enterobacter cloacae clinical isolate.

Abstract

This study describes the identification of the mcr-10.1 gene in a clinical isolate of an ST1 Enterobacter cloacae isolate cultured in 2015 in Kenya. The isolate was multidrug resistant, phenotypically non-susceptible to various antibiotics, including colistin. Whole genome sequence analyses indicated carriage of chromosomally encoded antimicrobial resistance genes and the colistin-resistant gene mcr-10.1 located on a 72-kb plasmid designated pECC011b with an IncFIA(HI1) replicon directly adjacent to tyrosine recombinase gene, xerC, and downstream of an ISKPn26 insertion sequence. Studies have shown that expression of mcr-10.1 may not be sufficient to confer colistin resistance, but a novel non-synonymous mutation (S244T) was identified in the phoQ gene known to influence colistin resistance within lipid modification pathways, which could have complemented the mcr-10.1 resistance mechanism. In silico analysis of the mutant phoQ protein shows the location of the mutation to be at the Histidine kinases, Adenyl cyclases, Methyl-accepting proteins and Phosphatases (HAMP) region, which plays a crucial role in the protein's activity. This study and our previous report of mcr-8 in Klebsiella pneumoniae indicate the presence of mobile mcr genes in the Enterobacterales order of bacteria in Kenya. The study points to the importance of regulation of colistin in the animal industry and enhancing surveillance in both human and animal health to curb the spread of mcr genes and accurately assess the risks posed by these mobile genetic elements in both sectors.IMPORTANCEThis paper reports the detection of new colistin resistance mechanisms in Kenya in a clinical isolate of Enterobacter cloacae in a patient with a healthcare-associated infection. The plasmid-mediated resistance gene, mcr-10.1, and a novel amino acid mutation S244T in the phoQ gene, located in a region of the protein involved in membrane cationic stability contributing to colistin resistance, were detected. Colistin is a critical last-line drug for multidrug-resistant (MDR) gram-negative human infections and is used for treatment and growth promotion in the animal industry. The emergence of the resistance mechanisms points to the potential overuse of colistin in the animal sector in Kenya, which enhances resistance, threatens the utility of colistin, and limits treatment options for MDR infections. This study highlights the need to enhance surveillance of colistin resistance across sectors and strengthen One Health policies that ensure antimicrobial stewardship and implementation of strategies to mitigate the spread of antibiotic resistance.