Emerging Mobile Colistin Resistance Gene Mcr-1 and Mcr-10 in Enterobacteriaceae Isolates From Urban Sewage in China.

Purpose: This study aimed to investigate the epidemiology and dissemination of mcr-positive Enterobacteriaceae in urban sewage in Yangzhou, China.

Methods: A total of 366 sewage samples were collected from the Yangzhou Wastewater Treatment Plant in Jiangsu Province. Colistin-resistant Enterobacteriaceae was identified through PCR targeting mcr-1 to mcr-10 genes. The isolates underwent antimicrobial susceptibility testing, and whole-genome sequencing was performed to analyze their genomic features. Additionally, conjugation experiments were conducted to assess the transferability of mcr-positive plasmids.

Results: Three mcr-positive Enterobacteriaceae isolates were identified, representing an isolation rate of 0.82%. These included one mcr-1-positive Escherichia coli (ST167) and two mcr-10-positive Klebsiella pneumoniae complex strains with novel sequence types ST6801 and ST6825. The mcr-1 gene was located on an IncI2 plasmid (pYZ22WS208_3) and successfully transferred to recipient strains. In contrast, the mcr-10 gene was carried on IncF plasmids (pYZ22WS067_1 and pYZ22WS223_1) but was not transferable in this study. Phylogenetic analysis revealed that the mcr-1-positive E. coli strain clustered within Clade II, alongside strains from various countries and sources. Phylogenomic analysis of mcr-10-positive isolates showed their sporadic distribution across 13 countries, with associations to diverse hosts and environments, indicating potential for widespread transmission.

Conclusion: This study demonstrates the presence of mcr-1 and mcr-10-positive Enterobacteriaceae in wastewater, emphasizing the importance of wastewater surveillance for tracking antibiotic resistance. The horizontal transfer of mcr-1 and potential spread of mcr-10 across various hosts underscore the need for ongoing monitoring and preventive measures.