NMCR-6, a novel nonmobile colistin resistance gene in Vibrio bacteria: full characterization and global perspective

Amid rising bacterial resistance, polymyxins are a critical last resort against multidrug-resistant Gram-negative infections. Understanding and predicting the emergence of novel, nonmobile colistin resistance (NMCR) genes are essential to preserving their efficacy and preventing potential resistance crises. Following the discovery of a high-level polymyxin B-resistant Vibrio harveyi strain WHSS0915, which exhibited antimicrobial resistance, we characterized the chromosomally encoded polymyxin-resistance protein NMCR-6 (WHSS0915). Through BLASTP searches against the Pan-Vibrio protein database, we identified the chromosomal eptA in Vibrio species as a NMCR (NMCR-6). We then investigated its global epidemiology and the potential determinants contributing to the spread of NMCR-6-bearing Vibrio strains. We identified and characterized the NMCR-6 protein in the V. harveyi strain WHSS0915. BLASTP searches based on the protein sequence revealed 14 158 sequences with over 60% homology to NMCR-6. Thirteen subtypes, named NMCR-6.1 to NMCR-6.13 according to the year of their earliest publication were classified. Phylogenetic analyses showed NMCR-6 variants form a distinctive branch among other mobile colistin resistance (MCR)/NMCR proteins. Statistical analysis of pathogenic Vibrio hosts carrying NMCR-6 revealed a broad distribution across different sample sources, detecting it in 7 clinically significant Vibrio species, notably V. parahaemolyticus . A global geographical analysis of NMCR-6 Vibrio hosts suggested that coastal extent, latitude, and temperature influence the distribution of NMCR-6 harboring Vibrio hosts. Our research defined and evaluated the global epidemiology of NMCR-6 in Vibrio species, revealing the dissemination of resistance genes within pathogenic Vibrio and the associated public health risks. This knowledge will aid in predicting the emergence of new mobile colistin resistance genes. • Dissemination of resistance genes among pathogenic Vibrio strains was studied. • Vibrio chromosome eptA gene was identified as nonmobile colistin resistance determinant 6 (NMCR-6). • Thirteen variants of NMCR-6 proteins were identified and named. • NMCR-6 displayed unique evolutionary characteristics with other MCR/NMCR variants. • Spatiotemporal distribution of NMCR-6 in its host Vibrio species was elucidated.