Unravelling the pathogenesis of Vibrio parahaemolyticus infection: impacts on antioxidant and innate immunity gene responses in Scylla paramamosain

This study investigated the etiology of Vibrio parahaemolyticus in mud crabs (Scylla paramamosain), a pivotal species in China's aquaculture industry. The results demonstrate that the V. parahaemolyticus strain LG2206 poses a significant threat to mud crabs by inducing oxidative stress and impairing their non-specific immune response. A 7-day immersion contagion test was conducted to determine the lethal dose 50 (LD50) of LG2206 for the mud crabs, which was established at 3.16 × 10⁵ CFU/mL. The findings indicate that LG2206 can infiltrate multiple tissues of the mud crab, with the gills being the initial and primary site of invasion, followed by the hepatopancreas, midgut, and muscle. Throughout the infection period, an increasing LG2206 count across sampled tissues led to tissue damage and cell death, with the gills, hepatopancreas, midgut, and muscle affected in sequence. The modulation of various enzymatic and genetic responses to LG2206 incubation was also investigated. Notably, superoxide dismutase (SOD) and glucocorticoid reductase (GR) were upregulated in the gill tissue. Phenoloxidase (PO) and lysozyme (LZM) exhibited a transient surge on the first day post-infection, followed by a decline. Enzymatic activity in other tissues followed a pattern of initially increasing, peaking, and then gradually declining, with the gills, hepatopancreas, midgut, and muscle following this trend sequentially. Additionally, the expression patterns of heat shock protein 70 (HSP70) and CASP-3 genes mirrored this trend, with their peaks occurring at different times across the various tissue types. In summary, this study sheds light on the pathogenic process of LG2206 in mud crabs, revealing that V. parahaemolyticus initially adheres to and compromises gill tissue before spreading through the circulatory system to other organs, with a preference for the hepatopancreas. This work enhances our understanding of the effects of V. parahaemolyticus on mud crab farming and proposes potential intervention strategies to mitigate its harmful impacts.