Abstract
To understand the dynamics behind the worldwide geographical spread of the mcr-1 gene, we investigated the population structure and genetic background of 410 Enterobacteriaceae, isolated from human, animal and environmental samples, and their mobile genetic elements carrying the mcr-1 gene.
All available whole genome sequences and MLST profiles of mcr-1-carrying E. coli isolates, along with 6 newly sequenced travel related isolates, were analysed for their phylogenetic relatedness. We show the presence of two clusters of mcr-1-carrying E. coli isolates that are possible reservoirs for the gene that, despite a high overall diversity of the population. One cluster is linked to ST10, a sequence type known for its ubiquity in human- and food-related environments. No clustering by geographical origin or isolation source (humans, animal or environment) could be identified.
The IncI2, IncX4 and IncHI2 plasmid incompatibility types accounted for more than 90% of 219 mobile genetic elements carrying the mcr-1 gene. We found significant geographical clustering consistent with regional spread of IncHI2 plasmids in Europe and IncI2 in Asia.
These findings point towards promiscuous spread of the mcr-1 gene by efficient horizontal gene transfer dominated by a limited number of plasmid incompatibility types.