Anti-Pressure Mechanism Of Pressure-Resistant Strains Of Vibrio Parahaemolyticus

V. parahaemolyticus is one of the main pathogens in seafood. High pressure could be used to control V. parahaemolyticus. Although a>250MPa pressure can kill the pathogen, it adversely affects seafood texture. Pressures which lower than this level have been shown to be ineffective in eliminating pressure-resistant V. parahaemolyticus from seafood.The mechanism of microbial resistance to high hydrostatic pressure by V. parahaemolyticus was studied in this paper. The pressure-resistant V. parahaemolyticus strains were separated and obtained by repeatly high hydrostatic pressure from80-250MPa. The survival rate, the permeability of membrane, the activity of ATPase, the components of soluble protein in cell membrane and the content of ion in cell both in pressure-sensitive and pressure-resistant V. parahaemolyticus were detected. Three intracellular antioxidant enzyme activities were also determined at the same high hydrostatic pressures; furthermore, fatty acid composition was analysed by GC-MS method, the differences in gene expression were detected by quantitative real-time PCR thus to reveal the pressure resistant mechanism at molecular level. The results are as follows:When exposed to a pressure of250MPa culturable cell counts of pressure-resistant strains was ca.3logs higher than that of pressure-sensitive strains.The pressure-resistant strains appeared to have a greater amount of soluble cell membrane protein of36KDa.The activity of Na+K+ATPase was83.3%more active than that of pressure-sensitive strains.The contents of potassium, sodium, calcium and magnesium ions were higher in pressure-sensitive strains compared with pressure-resistant strains, while the content of zinc ion was higher in pressure-resistant strains.After same pressure treatment, the activity of intracelluar enzyme decreased sharply in pressure-sensitive strains while smoothly in pressure-resistant strains.The ratio of unsaturated vs. saturated fatty acids of cell membranes was1.06in pressure-sensitive strains comparing to1.18in pressure-resistant strains, which was beneficial to cell complecity when exposed to high hydrostatic pressure with increased membrane fluidity.Subsequent qRT-PCR result showed that the expression of delta-9fatty acid desaturase increased in pressure-resistant strains, which was in accordance with the GC-MS analysis result.Results suggest that pressure-resistant V. parahaemolyticus may have survived the pressure treatments through the changes in the cell membrane composition and intracellular components.