Protective effects of gallic acid against Vibrio parahaemolyticus-induced translucent post-larvae disease in Litopenaeus vannamei: insights into antibacterial and anti-virulence mechanisms.

Translucent post-larvae disease (TPD) is a lethal syndrome causing high mortality in post-larvae of Litopenaeus vannamei. This study investigated the protective efficacy of gallic acid (GA), a non-antibiotic compound, against TPD induced by a field isolate Vibrio parahaemolyticus TS-GE (V. para. TS-GE). Immersion challenge assays confirmed the high virulence of V. para. TS-GE, as it caused 100 % mortality in post-larvae within 24 h at 2.82 × 107 CFU/mL. Whole-genome sequencing revealed its genome comprised two chromosomes (3.50 Mb and 1.92 Mb) and three plasmids (69.7 kb, 60.7 kb, 60.5 kb). The 69.7-kb plasmid harbored TPD-associated virulence genes vhvp1 and vhvp2, while chromosomal genes encoded 40 type III secretion system components and thermolabile hemolysin. Pangenome analysis revealed the open genome nature of V. parahaemolyticus strains. Multi-locus sequence typing identified V. para. TS-GE as ST2621. In vitro, GA exhibited growth-inhibitory activity against V. para. TS-GE. In vivo, 200 μg/mL GA significantly reduced cumulative mortality (P < 0.01) from 100 % to 18.3 %, preserving hepatopancreatic epithelium and midgut structure in V. para. TS-GE infected post-larvae. Mechanistic investigations revealed GA disrupted bacterial cell wall/membrane integrity, inhibited swimming motility, and suppressed biofilm formation. Molecular docking simulations predicted favorable binding of GA to virulence proteins VHVP1 (-6.3 kcal/mol) and VHVP2 (-7.8 kcal/mol), suggesting dual antibacterial and anti-virulence activities. These findings highlight GA as a promising antibiotic alternative for TPD control. Genomic data provide insights into the pathogenic adaptation of V. para. TS-GE in aquaculture.