Pathogenicity and Genomic Characterization of Vibrio parahaemolyticus VSP1: A Pathogen Linked to Enteritis Outbreak in Shrimp (Penaeus vannamei)

Enteritis is a common and recurrent disease in shrimp aquaculture, causing significant economic losses and management challenges. However, its specific causative pathogen remains unclear. Here, a pathogen strain, <i>Vibrio parahaemolyticus</i> VSP1, was directly isolated from shrimp with enteritis, and its pathogenicity and genomic characteristics were analyzed. Diseased shrimp exhibited lethargy, empty gut, hepatopancreatic atrophy, and severe intestinal damage. The gut bacterial community of diseased shrimp differed significantly from healthy shrimp (PERMANOVA, <i>p</i> < 0.05), with a 129% increase in <i>Vibrio</i> relative abundance. Nine <i>Vibrio</i> operational taxonomic units (OTUs) were enriched in diseased shrimp, and the dominant OTU1 shared 100% 16S rRNA identity with VSP1. VSP1 grew rapidly, utilized diverse carbon sources, and induced enteritis symptoms in over 90% of challenged shrimp. Genome analysis revealed 98.34% average nucleotide identity with <i>V. parahaemolyticus</i> ATCC 17802 and identified 156 putative virulence-related genes, mainly related to adherence, motility, and secretion systems. Unlike the strain ATCC 17802, VSP1 lacks thermostable direct hemolysin (TDH) and type III secretion system 2 (T3SS2), but contains alternative virulence factors such as <i>Yersinia</i>-like type IV pili and lipooligosaccharides, suggesting a distinct virulence strategy. This study identifies the pathogen responsible for shrimp enteritis and provides a foundation for targeted control strategies in aquaculture.