A variant of the multidrug-resistant gene MCR-1 was detected in a Salmonella typhimurium serovar, in a healthy patient in China. The MCR-1 gene plays a key role in bacterial ability to resist colistin. Colistin is one of the last-resort antibacterial drugs and is increasingly used for treating carbapenem-resistant Enterobacteriaceae. The MCR-1 enzyme modifies the chemical structure of lipid A moiety on bacterial LPS by the addition of phosphoethanolamine, which in turn reduces the binding affinity to colistin (i.e., producing the colistin resistance).
This is the first time an MCR-1 gene has been found in Salmonella in a healthy carrier. The reaserchers called the gene MCR-1.3 as it is a variant on MCR-1, a gene discovered in 2015 in China.