Phage controlling method against novel freshwater-derived Vibrio parahaemolyticus in ready-to-eat crayfish (Procambarus clarkii)

Vibrio parahaemolyticus is a halophilic foodborne pathogen majorly isolated from seafood, threatening public health worldwide. However, our recent study reported the presence of this bacterium in freshwater crayfish, which were rarely identified and investigated. Its pathogenicity and genomic features remain unclear, and the controlling method to inhibit this bacterium in ready-to-eat (RTE) crayfish is not developed. Compared with a clinical strain (ATCC17802), the representative strain (LVP1) from freshwater crayfish showed higher pathogenicity in a zebrafish model, indicating its hypervirulence and foodborne infection risk. Unlike most clinical V. parahaemolyticus isolates that carried tdh and (or) trh, two classic virulence factor genes associated with clinical infections, the hypervirulent LVP1 lacked these two genes, indicating it is a novel strain and other unknown virulence factors play key roles in its pathogenicity. Genomic and phylogenetic analyses demonstrated this strain is V. parahaemolyticus, while it is phylogenetically distant from other global isolates. Therefore, LVP1 is considered a novel V. parahaemolyticus strain from freshwater crayfish, being hypervirulent, and lacking virulence marker genes. The antimicrobial resistant genes drfA6 and qnrV1 were unique in LVP1 and absent in other reference V. parahaemolyticus strains. Antimicrobial susceptibility testing confirms it as multidrug resistance, with resistance to ampicillin, amoxicillin/clavulanate, trimethoprim, and colistin. To control this novel and multidrug-resistant V. parahaemolyticus strain in food production chains, we developed a phage cocktail and applied it to the surface of RTE crayfish meat, resulting in a significant decrease in the bacterial load by 2.36 log10 CFU/mL. These data highlight freshwater food products pose threats to public health through 'farm-to-fork' transmission of hypervirulent V. parahaemolyticus and reveal the phage cocktail as a promising method to attenuate this bacterium in RTE food, emphasizing the necessity to prevent food contamination caused by this bacterium from freshwater products.