Study On The Resistance Of Staphylococcus Aureus To High Hydrostatic Pressure After Some Different Sublethal Stresses

The study target of this paper were strain of Staphylococcus aureus ATCC 6538,with the purpose of studying the development of resistance responses in ATCC6538 to high hydrostatic pressure(HHP)treatment after the exposure to different stressful conditions such as excessive temperatures,acid and alkaline pH and disadvantageously osmotic stress.The feasibility of application of stress can effectively induced cross protection to HHP was evaluated.On the basic of above studies,the resistance models of ATCC6538 was established and the mechanism of stress induced resistance to HHP in the level of membrane fatty acid and the membrane F1F0-ATPase activity was discussed,which provided credible theroy evidence for control of ATCC6538 in High-pressure Technology on Food Sterilization.First of all,the resistance data of ATCC6538 incubated at different temperatures was obtained under the conditions of the pressures from 100 MPa to 500 MPa.Then Linear,Weibull,and Gompertz models were selected to fit the curves of resistance to HHP of ATCC6538.Regression coefficients(R2),root mean square error(RMSE),accuracy factor(At)and bias factor(Bf)were used to evaluate the goodness of fit for the three models.Results showed that the Linear model provided a poor fit for the data,which has minimum R2(0.8870),and Weibull model and Gompertz model showed suitable goodness-of-fit at five pressure levels between 100 MPa to 500 MPa(R2>0.9467).The Weibull model,which has maximum R2(0.9956)and minimum RMSE(0.0312),could be fitted perfectly to the curves of resistance to HHP in the three models.In conclusion,Weibull model showed ideal goodness-of-fit to the curves of resistance to HHP inactivation of ATCC6538.Resistance of ATCC6538 to HHP has varying degrees of increase after treatment of different sublethal stress.First,with increasing growth temperatures from 15℃ up to 45℃,the experimental results showed that the pressure resistance of ATCC6538 increased markedly(P>0.05).The pressure resistance of ATCC6538 under high temperature(45℃)is 2.6 times the size of the pressure resistance of ATCC6538 under low temperature(15℃).Second,the findings of our study indicate that the development of cross resistance to HHP resulted in an increasing trend with the increase of NaCl concentrations.Finally,conditions resulting in the maximum development of pressure resistance were pH 5.5 and pH 9.5.When ATCC6538 cells were exposed elevated acid or alkali stress(pH 2.5 or 12.5)failed to provide them with cross-protection against HHP.The aim of this work was to determine the alteration of the membrane fatty acid profile as an adaptive mechanism of the ATCC6538 cells to HHP stress.Gas chromatography(GC)and differential scanning calorimetry(DSC)were applied in this work.Analysis of the relationship between the membrane phospholipids melting point(Tm),the membrane flow index(FI)and the parameters(δ)of resistance to HHP of the ATCC6538 cells.The results showed that when the membrane phospholipids melting point decreased,the membrane flow index increased.With parameters of resistance to HHP in ATCC6538 after treatment of different temperatures,different concentrations of sodium chloride and different pHs increasing,the membrane flow index increased as well.Study the alteration of the membrane enzyme activity of the ATCC6538 cells to HHP stress after treatment of different temperatures,different concentrations of sodium chloride and different pHs.Analyze the relationship between membrane enzyme activity and pressure resistance of ATCC6538.The results showed that the pressure resistance of ATCC6538 under high temperature(45℃)increased markedly and Na+K+-ATPase,Ca2+Mg2+-ATPase and F1F0-ATPase activities of membrane of the ATCC6538 cells under high temperature(45℃)increased as well(P<0.05).The findings of our study indicate that the development of pressure resistance of ATCC6538 resulted in an increasing trend with the increase of NaCl concentrations.Na+K+-ATPase and Ca2+Mg2+-ATPase activities of membrane of the ATCC6538 cells increased(P<0.05).At the same time,F1F0-ATPase activities of membrane of the ATCC6538 cells increased first and then recovered to the normal level.Conditions resulting in the maximum development of pressure resistance were pH 5.5 and pH 9.5.When ATCC6538 cells were exposed elevated acid or alkali stress(pH2.5 or 12.5)failed to provide them with cross-protection against HHP.The results showed that Na+K+-ATPase and Cat+Mg2+-ATPase activities of membrane of the ATCC6538 cells increased(P<0.05)after treatment of pH 5.5 and pH 9.5 and decreased after treatment of pH 2.5 and pH 12.5.The activity of F1F0-ATPase of the ATCC6538 under pH 7.5 was used as control and discovered that the activity of FiF0-ATPase was increased(P<0.05)with the decrease of pH value and increased first and then decreased with the increase of pH value.