Influence of environmental parameters on total and pathogenic Vibrio parahaemolyticus isolated from mussels and clams.

Bivalve consumption presents a public health risk due to contamination with Vibrio parahaemolyticus, a leading cause of seafood-borne gastroenteritis. This study assessed the occurrence, pathogenicity, antimicrobial resistance, and biofilm-forming ability of V. parahaemolyticus in mussels and clams collected from the Aegean, Marmara, and Black Seas in Türkiye between May 2021 and May 2022. A total of 255 samples (135 mussels, 120 clams) were analyzed. The bacterium was detected in 32.2% of samples, with the highest occurrence (52.5%) observed in the low-salinity Black Sea. Pathogenic strains, carrying the trh gene, constituted 5.9% of all strains and were more frequently found in clams and during winter. All strains exhibited multidrug-resistance (MDR), showing resistance to at least four antimicrobial classes; notably, all were resistant to piperacillin and tetracycline. Biofilm formation assays revealed significant effects of temperature and incubation time: maximum biomass was observed at 25 °C after 48 h, while lower or higher temperatures, as well as shorter incubation, inhibited formation. Moderate biofilm production was observed only in clam-derived strains (7.1%). These findings demonstrate the influence of environmental and host-related factors on V. parahaemolyticus ecology and stress the need for species-specific monitoring strategies to safeguard seafood safety.