Abstract: 【Objective】 The experiment was aimed to investigate the effects of sodium butyrate on the growth and virulence of Aeromonas hydrophila, to assess the antibacterial activity of sodium butyrate against Aeromonas hydrophila, and to explore its mechanism of action.【Method】 The minimum inhibitory concentration (MIC) of sodium butyrate on Aeromonas hydrophila was determined by micro-broth dilution method, the effect of sodium butyrate on the motility of Aeromonas hydrophila was examined by swimming and cluster motility assay, the effect of sodium butyrate on lipase, protease and hemolysis of Aeromonas hydrophila was examined by using enzyme activity and hemolysis assay, the effect of sodium butyrate on the biofilm of Aeromonas hydrophila was examined by biofilm assay, and the fluorescence quantitative PCR was used to detect the effect of sodium butyrate on the virulence of Aeromonas hydrophila and the expression of genes related to the population sensing system.【Result】 The MIC of sodium butyrate was >512 mg/L for all three strains of Aeromonas hydrophila, and the growth of the three strains of Aeromonas hydrophila was not affected when the concentration of sodium butyrate was ≤ 512 mg/L.When the concentration of sodium butyrate was ≥ 64 mg/L, the growth of the three strains of Aeromonas hydrophila was not affected.When the concentration of sodium butyrate was ≥ 64 mg/L, it significantly inhibited the motility of the three Aeromonas hydrophila strains (P<0.05), except for the cluster motility of GZ-SS2019 (P>0.05), which also significantly inhibited the biofilm formation of the three Aeromonas hydrophila strains at this concentration (P<0.05).At the concentration of 128 mg/L, sodium butyrate had less effect on the lipase activity of the three Aeromonas hydrophila strains (P>0.05), but significantly inhibited the protease activity of the three Aeromonas hydrophila strains (P<0.05). When the concentration of sodium butyrate was ≥ 32 mg/L, it significantly reduced the hemolysis rate of the remaining two Aeromonas hydrophila strains(P<0.05), except for the inhibition of GZDX-01, which was not significant (P>0.05).The fluorescence quantitative PCR results showed that when the concentration of sodium butyrate ≥ 128 mg/L, it significantly reduced the expression of luxS and ahyR genes in the population induction system (P<0.05), the expression of aerA, ompW, ompA and fur genes were also significantly reduced (P<0.05).【Conclusion】 It was shown that sodium butyrate with the concentration was ≤ 512 mg/L did not affect the growth of Aeromonas hydrophila, but could effectively interfere with the motility status, protease activity, hemolysis, and biofilm formation and expression of virulence genes and population sensing system of Aeromonas hydrophila, and when the concentration was ≥ 128 mg/L, it was more effective.

Key words: sodium butyrate; Aeromonas hydrophila; biofilm; hemolysis; protease activity