Introduction of the transmissible mobile colistin resistance genes mcr-3 and mcr-9 to the USA via imported seafood

Abstract

Colistin, an important antibiotic, is used to treat certain bacterial infections in humans that can be severe and/or life-threatening. However, these bacteria can acquire the mobile colistin resistance ( mcr ) genes and become resistant to this antibiotic. Plasmid-borne mcr can jump between bacterial species, spreading in bacteria across a variety of hosts and niches. Therefore, monitoring the spread of mcr is critical to maintain the efficacy of colistin. In the USA, the occurrence of mcr in domestically produced food is thought to be limited. In this study, we showed that mcr can be carried into the USA by bacteria on imported seafood. A specific gene, mcr-9 , was located on a plasmid that could be transferred to other bacteria. Therefore, imported seafood can be an overlooked source of mcr in the USA. It is important to monitor and assess mcr in imported seafood to control the proliferation of colistin resistance in the USA.