Salinity-induced virulence alteration of Aeromonas hydrophila isolated from Scatophagus argus: insights from...

The emerging foodborne pathogen, Aeromonas hydrophila, co-infects humans and animals, especially fish, threatening aquacultural production and public health. Previously, we found that Scatophagus argus, a widely cultivated fish species with high economic value, exhibited enhanced growth but increased susceptibility to A. hydrophila infection under freshwater conditions compared to seawater conditions. However, the exact mechanisms involved remain unclear.

Our study demonstrated that the enhanced virulence of A. hydrophila 201416, isolated from S. argus, in response to increasing salinity was associated with altered quorum sensing-related gene expression and regulated behaviors. Results from virulence assays incorporating phenotypic characterization indicated that elevated salinity levels (from 0 to 35‰) significantly hindered Ah201416 infection of S. argus. This trend correlated with increased biofilm mass and swimming motility, yet was inversely related to bacterial growth. RNA-sequencing and quantitative reverse transcriptional PCR analysis confirmed significant upregulation of genes related to flagellar assembly (flgB, flgH, flgC, flgI, flhA, and fliA), bacterial secretion (HlyD and Ahh1), and quorum sensing (AhyR, LuxO, and LuxE) of Ah201416 in response to elevated salinity. These findings suggested that increased salinity not only enhanced the virulence of Ah201416 but also bolstered the resistance of S. argus, thereby mitigating its susceptibility.

This study provides deeper insights into the microbial risks associated with A. hydrophila in aquacultural production, which is critical to developing effective prevention and control strategies and ensuring a safe seafood supply.

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