Outbreak of vibriosis associated with Vibrio parahaemolyticus in the mud crab Scylla paramamosain cultured in China.

In this study, a Gram-negative bacterium was isolated from diseased Scylla paramamosain and tentatively named strain QX17. The bacterial isolate was identified as Vibrio parahaemolyticus based on morphological and biochemical characteristics and molecular identification with the 16S rRNA and HSP60 genes. In the challenge experiment, S. paramamosain injected intramuscularly with the V. parahaemolyticus isolate developed pathological signs similar to the naturally diseased mud crabs. The infection experiment also showed that the median lethal dosage (LD50) for QX17 was 4.79 × 102 CFU g-1 (crab weight). Histopathological analysis of the diseased mud crabs infected with V. parahaemolyticus showed deformation and basement membrane rupture of hepatopancreatic tubules in the hepatopancreas, and disordered and broken muscle fiber in the muscle. Antimicrobial susceptibility tests revealed that QX17 was highly sensitive to most of the tested aminoglycosides, tetracyclines, and quinolones. To the best of our knowledge, this is the first study reporting isolation and antibiotic sensitivities of V. parahaemolyticus from cultured mud crabs. The discovery of V. parahaemolyticus in cultured mud crabs not only adds to the growing list of emerging pathogens in crab aquaculture in China, but also highlights the necessity of developing early detection strategies and appropriate interventions to reduce the damage caused by V. parahaemolyticus in mud crab aquaculture.