Combined effects of polyamide microplastics and the pathogenic bacterium Vibrio parahaemolyticus on the immune parameters of Mytilus coruscus

The thick-shelled mussel, Mytilus coruscus, plays a vital role in marine ecosystems but is vulnerable to pollutants. Polyamide microplastics (PA-MPs), such as nylon, can adsorb harmful bacteria like Vibrio parahaemolyticus, posing threats to bivalves and economic risks to aquaculture. In this study, M. coruscus was exposed to four treatments over 14 days: (1) control, (2) PA microplastics (50 particles/L), (3) V. parahaemolyticus (10¹¹ CFU/L), and (4) combined PA and V. parahaemolyticus. Evaluations included gill tissue pathology, bacterial loads in mussel tissues, and antioxidant and immune enzyme activities in hemolymph. Results showed that co-exposure to PA microplastics and V. parahaemolyticus led to gill tissue damage, such as decreased gill epithelial thickness and hemocytic infiltration. In addition, mussels exhibited elevated oxidative stress in the hemolymph, as indicated by increased levels of hydrogen peroxide (H₂O₂), superoxide anion (O₂^·-), and malondialdehyde (MDA). Concurrently, immunological activity was suppressed, as evidenced by reduced activities of alkaline phosphatase (AKP), acid phosphatase (ACP), and lysozyme (LZM). Notably, PA microplastics appeared to facilitate the clearance of V. parahaemolyticus by the mussels. These findings contribute to sustainable aquaculture and shellfish safety strategies.