Emergence of colistin-resistant hypervirulent (CoR-HvKp) in China.

Colistin is regarded as a last-resort agent to combat infections caused by multidrug-resistant (MDR) Gram-negative bacteria, especially carbapenem-resistant isolates. In recent years, reports of colistin-resistant (CoRKp) are increasing. However, the molecular mechanism and relevance of colistin resistance and virulence remain unclear. Fourteen CoRKp strains were retrospectively screened from 1884 clinical isolates during 2017-2018 in China. Six CoRKp strains belonging to ST11 were MDR strains. Plasmid-mediated mobile colistin-resistance genes had a low prevalence in CoRKp. Our results revealed that up-regulated expression of two-component systems, especially contributed more to colistin resistance. mutation was the most common molecular mechanism of colistin resistance, caused by either nonsense mutations or insertion sequences, which drove the overexpression of . This study also identified three novel point mutations in system, in which D313N mutation in was proved to increase the MIC to colistin by 16-fold. In addition, 6 out of 14 CoRKP strains independently carried hypervirulence genes. All six strains showed medium-to-high virulence phenotype compared with NTUH-K2044 strain in mice intraperitoneal challenge models. We found that 4 strains were biofilm strong producers and transcriptome analysis revealed that three of them significantly up-regulated expression of type III fimbrial shaft gene . In conclusion, our result revealed the emergence of colistin-resistant and hypervirulent MDR which is a noticeable superbug and could cause a severe challenge to public health.