Abstract:In order to reveal the mechanisms underlying the antibacterial function of protocatechuic acid (PCA), the antimicrobial activity and virulence-attenuating effect of PCA was investigated. To evaluate the antibacterial activity of PCA against Vibrio parahaemolyticus and its effect on the integrity and permeability of cell membranes, the minimal inhibitory concentration (MIC), growth curve, nucleotide and protein leakage, and malondialdehyde (MDA) content were measured, and the morphological changes of V. parahaemolyticus were examined by scanning electron microscopy. Meanwhile, the virulence-attenuating effect of PCA against V. parahaemolyticus was further investigated through detecting the effects of PCA at sub-inhibitory concentrations (SICs) on the synthesis of virulence factors of V. parahaemolyticus. The experimental results showed that the MIC of PCA against V. parahaemolyticus was 2 mg/mL. After the treatment with PCA at MIC, V. parahaemolyticus was severely invaginated and ruptured. The contents of nucleic acid, protein, and MDA in the supernatant were 2.65 times, 1.94 times, and 10.05 times those of the control group, respectively. In addition, the inhibition rates of PCA against extracellular polysaccharides, extracellular proteases, and biofilms were 40.57%, 19.79%, and 26.04%, respectively, at a PCA concentration of 1/4 MIC, and 52.85%, 28.38% and 34.69%, respectively, at a PCA concentration of 1/2 MIC. PCA mainly acted on cell membrane, inhibited the growth of V. parahaemolyticus through affecting the integrity and permeability of the cell membrane, and at sub-inhibitory concentrations reduced effectively the virulence of V. parahaemolyticus.
