Companion animals as sources of hazardous critically important antimicrobial-resistant Escherichia coli: Genomic surveillance in Shanghai.

This study provides the first comprehensive genomic surveillance of critically important antimicrobial (CIA)-resistant Escherichia coli in companion animals, addressing gaps in the understanding of antimicrobial resistance (AMR) transmission dynamics and the environmental dissemination of hazardous resistance genes within urban ecosystems. A total of 244 CIA-resistant Escherichia coli (CIA-EC) isolates were obtained from 730 anal swabs collected across 11 pet hospitals in Shanghai. High-risk zoonotic clones, such as ST410 and ST405, were identified across multiple districts, with blaNDM-5-positive IncX3 plasmids demonstrating exceptional stability, efficient conjugation, and broad host adaptability. These plasmids significantly amplify the global risk of cross-species blaNDM-5 dissemination. Mobile genetic elements (ISKox3, IS5, ISAba125) further facilitated blaNDM-5 transfer, enhancing the persistence and adaptability of these zoonotic pathogens. Additionally, novel sequence types (ST87, ST12624) exhibited resistance to last-resort antimicrobials, including tigecycline (tet(X4)), exacerbating the public health risks. The findings demonstrate that companion animals serve as critical reservoirs at the human-animal-environment interface, facilitating the environmental spread of hazardous resistance elements such as blaNDM-5-positive IncX3 plasmids. Integrating companion animals into One Health AMR surveillance and implementing antimicrobial stewardship are crucial to mitigating the spread of CIA-resistance determinants and preserving the efficacy of last-resort antimicrobials.