Epidemiology, genetic dynamics, and transmission of the <i>mcr-1</i> gene in China

Colistin is a broad-spectrum antibiotic that kills bacteria through the disruption of the cell membrane, making it effective against various bacterial infections. Since the first global report of <i>mobile colistin-resistant</i> (<i>mcr-1</i>)-positive bacteria, which were discovered and described by Chinese scientists in 2015, monitoring and research on these bacteria have continuously been conducted. In this study, we analyzed 70 <i>mcr-1</i>-positive strains detected by surveillance hospitals across three different provinces of China, as well as 671 strains screened from the NCBI database that contain the <i>mcr-1</i> gene. The epidemiological analysis indicated that the <i>mcr-1</i> gene had circulated undetected in China for over three decades prior to its first report in 2015 and extensive agricultural use of polymyxins likely initiated the emergence of <i>mcr-1</i> and <i>bla</i>_NDM co-harbouring strains in poultry and livestock, with subsequent fecal-environmental transmission leading to human infections. The genetic dynamics and transmission analysis provides the first detailed elucidation of the adaptive evolutionary migration of <i>mcr-1</i>, which enhanced its dissemination across diverse bacterial hosts and facilitated the emergence of super-resistant <i>Enterobacterales</i> strains and IncHI2(A) super-plasmids co-harbouring <i>mcr-1</i> and <i>bla</i>_NDM.