Decoding the origins, spread, and global risks of mcr-9 gene

Area of Science:

• Microbiology
• Genetics
• Epidemiology

Background:

• The plasmid-mediated mobilized colistin resistance (mcr) gene family threatens last-line antibiotic defense.
• mcr-9 is the second most prevalent variant, following mcr-1.

Purpose of the Study:

• To reconstruct the historical trajectory and transmission dynamics of the mcr-9 gene.
• To investigate the host tropism and plasmid-based transmission mechanisms of mcr-9.
• To assess the global dissemination and clinical implications of mcr-9.

Main Methods:

• Compiled a dataset of 698 mcr-9-positive isolates from 44 countries.
• Utilized Bayesian analysis to reconstruct the historical spread of mcr-9.
• Employed effective reproduction number to analyze transmission dynamics.

Main Results:

• mcr-9 originated in the 1960s, expanding globally from Western Europe.
• mcr-9 exhibits a preference for transmission within Enterobacter, potentially driven by plasmid codon usage bias.
• Low colistin resistance of mcr-9 facilitated silent global spread, but high-expression strains are emerging.

Conclusions:

• The adaptability and dissemination potential of mcr-9 present a significant challenge to antimicrobial resistance control.
• Clinical emergence of high-expression mcr-9 strains necessitates urgent attention within the One Health framework.