Abstract
Background:
Vibrio parahaemolyticus is a major foodborne pathogen associated with raw or undercooked fish. Hypochlorous acid (HOCl) is a widely used sanitizer; however, its antimicrobial performance may be influenced by formulation components, such as surfactants, that enhance surface penetration.

Aim:
This study aimed to evaluate the short-term antimicrobial efficacy of HOCl combined with different surfactants on Nile tilapia (Oreochromis niloticus) filets contaminated with Vibrio spp. and to assess associated physicochemical changes and virulence gene expression.

Methods:
Nile tilapia filets were screened for Vibrio spp., and V. parahaemolyticus was confirmed using species-specific 16S rRNA and toxR genes. The filets were assigned to four experimental groups: a control group treated with phosphate-buffered saline (G1), and three treatment groups receiving HOCl (20 ppm) combined with polysorbate 80 (0.5%; G2), lecithin (1%; G3), and distilled monoglyceride (1%; G4). Antimicrobial activity was evaluated over a 20-min exposure period by enumerating total Vibrio counts. Physicochemical parameters (pH, electrical conductivity, total dissolved solids, salinity, and residual chlorine) were measured, and toxR gene expression was assessed using quantitative PCR.

Results:
All HOCl–surfactant treatments significantly reduced Vibrio counts compared with the control. The greatest microbial reduction was observed in the monoglyceride group (4.41 log CFU/g), followed by polysorbate 80 (3.90 log CFU/g) and lecithin (3.71 log CFU/g). The treated filets exhibited lower pH values and increased electrical conductivity, total dissolved solids, and salinity, with the highest changes recorded in the monoglyceride group. Residual chlorine levels remained within acceptable limits. Quantitative polymerase chain reaction analysis showed significant downregulation of the toxR virulence gene, with lecithin treatment producing the greatest suppression (0.1377-fold).

Conclusion:
Combining HOCl with lipid-based surfactants enhances its immediate antimicrobial activity against V. parahaemolyticus and reduces virulence gene expression while inducing measurable physicochemical changes in fish filets. These results support the potential application of HOCl–surfactant formulations as short-term decontamination treatments to improve seafood safety. However, further storage studies are required to determine their impact on shelf life.

Key words: Food safety; HOCl; Nile tilapia; Vibrio parahaemolyticus; Virulence gene.