Effects Of Temperature On Inactivation Heterogeneity And Biofilm Heterogeneity Of Foodborne Pathogens

Microbial risk assessment is one of the most important scientific tools to ensure food safety.It is crucial for the development of food safety policies,regulations and standards.Strain heterogeneity diversity is the inherent characteristic of microorganisms,which is prevalent in various pathogens,affecting the accuracy and uncertainty of microbiological risk assessment.Little information is available on the concrete influence of strain heterogeneity diversity of foodborne pathogen to microbial risk assessment.Strain heterogeneity diversity was firstly proposed and its main types were summarized which include growth and death heterogeneity,biofilm heterogeneity,virulence heterogeneity and antibiotic resistance heterogeneity.In food processing and storage,temperature has a great influence on the strain heterogeneity,especially on the growth and death heterogeneity,biofilm heterogeneity.Therefore,To study the effect of temperature on inactivation heterogeneity and biofilm heterogeneityof food-borne pathogenic bacteria,were expected to weakening the influence of heterogeneity diversity and improving the accuracy and uncertain of microbial risk assessment.In this study,food-borne pathogenic bacteria(Vibrio parahaemolyticus,Listeria monocytogenes and Escherichia coli)were used.Firstly,the inactivation heterogeneity of Vibrio parahaemolyticus was analyzed under the conditions of sterilization(65?)and storage temperature(10?);Secondly,the changes of the pre-formed biofilm of Vibrio parahaemolyticus at low temperature(4? and 10?)were investigated;Finally,the changes of biofilm pre-formed of Listeria monocytogenes and Escherichia coli at low temperature(4? and 10?)were investigated,and the pre-formed biofilm heterogeneity of three food-borne pathogens was analyzed.The main contents of this study were summarized as follows:1.Study on the inactivation variability of Vibrio parahaemolyticus under sterilization and storage temperature in food industryThis paper studies inactivation variability of 19 Vibrio parahaemolyticus in the food industry at pasteurization temperature(65°C)and cold chain temperature(10°C),fit data with the Weibull model,receive the inactivation parameters(t_R),explore the inactivation variability among the different strains.Results show that under the condition of 65°C,the t_R values of 19 Vibrio parahaemolyticus between22.619~67.229 s,VPC-1 was the most heat resistant strains,VPC-10 was the least heat resistant strains,the optimum probability distribution of heat inactivation t_R values was Normal(44.817,12.266).Under the cold inactivation condition of 10°C,the t_R values between 113.954~371.383 h,VPC-3 was the cold resistant strains,VPC-2 was the least cold resistant strains,the optimum probability distribution of cold inactivation t_R values was LogLogistic(51.450,148.88,4.6648).The results of this study showed that there was no significant correlation between thermal inactivation and cold inactivation of Vibrio parahaemolyticus,the inactivation variability of the bacterial strain was widely existed in Vibrio parahaemolyticus,and the present inactivation model was only based on a single strain,so it was difficult to describe the overall inactivation trend.At the same time,a random model of bacterial inactivation variability was preliminarily constructed,and the traditional inactivation parameters were replaced by the probability distribution,so as to provide a reliable scientific tool for the risk control of vibrio parahaemolyticus in the food industry.2.Effect of low temperature stimulation on the formation of preformed biofilm by Vibrio parahaemolyticus.2.Cold Shock Fail to Restrain Pre-formed Vibrio parahaemolyticus BiofilmThe aim was to analyze changes of pre-formed Vibrio parahaemolyticus biofilm under cold shock(4°C and 10°C).We show that V.parahaemolyticus biofilm biomass increased significantly during this cold shock period and there was a gradual increase of polysaccharides and proteins content in the extracellular polymeric matrix(EPS).In addition,we demonstrate that the expression of flagella and virulence-related genes were differentially regulated.The architecture of the biofilm,quantified using mean thickness(MT),average diffusion distance(ADD),porosity(P),biofilm roughness(BR)and homogeneity(H)also changed during the cold shock and these parameters were correlated(P<0.01).However,the correlation between biofilm architecture and biofilm-related genes expression was relatively weak(P<0.05).Cold shock at 4°C and 10°C is not sufficient to reduce V.parahaemolyticus biofilm formation and strategies to reduce risk of foodborne infections should take this information into account.3.Analysis of preformed biofilm heterogeneity of foodborne pathogens under cold shockIn this paper,the development and changes of preformed biofilm by Listeria monocytogenes and E.coli under cold shock were analyzed,and the heterogeneity of preformed biofilm by Vibrio parahaemolyticus,Listeria monocytogenes and E.coli was analyzed.The results showed that the total biofilms of Listeria monocytogenes and E.coli increased under cold shock,and the extracellular polysaccharides also increased gradually.The average thickness(MT),average diffusion distance(ADD),porosity(P),biofilm roughness(BR)and uniformity(H)of biofilm also changed during cold shock.Compared with Listeria monocytogenes and Vibrio parahaemolyticus,the biofilm structure of E.coli changed greatly.The results showed that the preformed biofilm of foodborne pathogens had great heterogeneity under cold shock.