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. Plain Language Summary: 1. Colistin resistant Enterobacteriaceae isolates were identified in urban sewage. 2. The common genotypes revealed were mcr-1 and mcr-10 . 3. Urban sewage may serve as a reservoir for antibiotic resistance genes, presenting a significant risk to public health.