International journal of antimicrobial agents | 2021
Molecular genetic characteristic of mcr-9-harbouring Salmonella enterica Serotype Typhimurium isolated from raw milk: mcr-9 in Salmonella enterica Serotype Typhimurium from raw milk.
Abstract
Among the 10 reported mcr genes, mcr-9 was firstly identified in Salmonella enterica Serotype Typhimurium, which was a leading cause of foodborne illness worldwide. But information about the prevalence and genetic features of mcr-9 is still lacking, especially among food samples. In this study, we found that mcr-9 had emerged in raw milk samples from China at a low prevalence rate of 0.83% (1/120). The mcr-9 was located on a transferable plasmid, and it was stable in wild-type S. enterica, however, it caused biological fitness cost when transfered to E. coli recipient. WGS revealed that the mcr-9 was located on IncHI2A-type plasmid, and surrounded by IS903B and IS26 in its flanking regions. The mcr-9-carrying S. enterica 19SE belonged to ST26 and presented multi-drug resistance phenotype. It was confirmed that mcr-9 did not mediate colistin resistance in our study, indicating its transfer may not facilitate the dissemination of colistin resistance.