Clinical emergence of a novel sequence type (ST3672) NDM-1-producing Vibrio parahaemolyticus in foodborne disease

This study characterized a newly identified ST3672-type Vibrio parahaemolyticus (V. parahaemolyticus) strain (VP1434), isolated directly from a patient involved in a food poisoning outbreak, highlighting its rare multidrug resistance (MDR) phenotype. The objectives were to investigate its resistance mechanisms, elucidate its evolutionary relationships, and assess its pathogenicity.

The VP1434 isolate was analyzed as follows: (1) Antimicrobial susceptibility was tested against 29 antibiotics, and plasmid conjugation experiments verified drug resistance in recipient strains post-transfer. (2) Whole-genome sequencing was used to characterize its genomic features, including plasmid sequences and inter-plasmid relationships. (3) Evolutionary tracing of VP1434 and the plasmid pVP1434-NDM was performed by constructing phylogenetic trees. (4) Virulence factors (VFs) were identified via the Virulence Factor Database, and pathogenicity was assessed through mouse infection.

The strain demonstrated a concerning MDR profile, exhibiting resistance to all tested β-lactam antibiotics. Additionally, it displayed resistance to sulfonamides and aminoglycosides, with intermediate susceptibility to tetracyclines. Plasmid conjugation experiments showed the bla _NDM-1-harboring plasmid was transferable to VP0577, and transconjugants also showed MDR. Whole-genome sequencing identified a bla _NDM-1-carrying plasmid harboring multiple resistance genes, which fully explaining its phenotypic resistance to at least four classes of antibiotics. Phylogenetic analysis placed VP1434 on a distinct branch within the maximum-likelihood tree constructed from global V. parahaemolyticus isolates, while the closest relative of the bla_NDM-1 -harboring plasmid was identified in a shrimp-derived V. parahaemolyticus strain. VP1434 was found to harbor 185 VFs, including tlh and trh, but lacked the key pathogenicity determinant tdh. In mouse infection experiments, strain VP1434 (tdh^-/trh⁺ ) exhibited significantly higher lethality than environmental isolates (tdh^-/trh^- ), suggesting TRH plays a significant role in pathogenicity even in the absence of TDH.

This first report of bla _NDM-1-positive clinical V. parahaemolyticus reveals plasmid-mediated MDR emergence in human infections. Its unexpected virulence without classical toxins indicates evolutionary adaptation, necessitating diagnostic updates and strengthened surveillance.