High occurrence of colistin- and multidrug-resistant strains carrying mcr-1 or an underestimated mcr-1.26 allelic variant along a large Brazilian river

Plasmid-mediated colistin resistance genes (mcr) are widely dispersed in different Enterobacterales species and niches, raising concerns about colistin use. The mcr-1.1 allele is globally distributed at the expense of an epidemic IncX4 plasmid circulating efficiently between humans and foodborne animals [1]. Much less is known regarding the contribution of natural environments to mcr spread, especially in countries with poor sewage treatment systems and high rates of antimicrobial-resistant bacteria such as Brazil [2]. We hereby performed a detailed whole genome analysis on colistin-resistant strains recovered along one of the largest rivers in the Ribeirão Preto mesoregion in Brazil.