Yujing Zhang,1– 3 Jiajie Chen,1– 3 Xinyu Yang,1– 3 Yangshiyu Wu,1– 3 Zhenyu Wang,1– 3 Yawen Xu,4 Le Zhou,4 Jing Wang,1– 3 Xinan Jiao,1– 3 Lin Sun1– 3 

1Jiangsu Key Laboratory of Zoonosis, Yangzhou University, Yangzhou, People’s Republic of China; 2Jiangsu Co-Innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou University, Yangzhou, People’s Republic of China; 3Key Laboratory of Prevention and Control of Biological Hazard Factors (Animal Origin) for Agrifood Safety and Quality, Ministry of Agriculture of China, Yangzhou University, Yangzhou, People’s Republic of China; 4Yangzhou Center for Disease Control and Prevention, Yangzhou, People’s Republic of China

Correspondence: Xinan Jiao, Email jiao@yzu.edu.cn; Lin Sun, Email sunlin@yzu.edu.cn

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.

Keywords: mcr, Enterobacteriaceae, urban sewage, antibiotic resistance, whole genome sequencing