First detection of IncHI2 plasmid carrying blaNDM-5 in Escherichia coli from retail shellfish.

The increasing dissemination of carbapenemase-producing Enterobacterales (CPE) across multiple ecological niches underscores a critical One Health challenge. Despite documentation of CPE contamination in shrimp, the occurrence of CPE within broader aquatic food products remains underexplored. In this study, 262 retail shellfish samples from farmers' markets were screened for blaNDM-producing Gram-negative bacteria. Three Escherichia coli (ST6769, ST10, and ST3871) and five Shewanella algae (unable to assign ST) isolates recovered from eight (3.1%) shellfish samples were identified as carrying blaNDM. Hybrid assembly confirmed the presence of a blaNDM-5-carrying IncHI2 plasmid in one Escherichia coli isolate and blaNDM-1 on untypeable plasmids in Shewanella algae. Both IncHI2 and untypeable plasmids shared highly similar structures with plasmids from various sources in the GenBank database. This is the first study to report the detection of IncHI2 plasmids carrying blaNDM-5 from retail shellfish. The widespread distribution of these plasmids may facilitate the dissemination of blaNDM in aquatic food products.