On The Study Of The Growth Variability Of Vibrio Parahaemolyticus In Aquatic Product

Vibrio parahaemolyticus is one of the major food-borne pathogens in aquatic products.For food safety ensurance,the quantitative risk assessment of Vibrio parahaemolyticus can effectively prevent and control the contamination of Vibrio parahaemolyticus in aquatic products.While the quantitative microbial risk assessment requires the scientific construction of the growth prediction model of Vibrio parahaemolyticus,taking into account factors that affect the growth heterogeneity of Vibrio parahaemolyticus,including temperature,salinity,source,medium and its intrinsic genotype.The growth status of different strains in the same experimental environment showed the growth heterogeneity of multi-strain complex,and the multi-strain growth macro model based on different influencing factors should be built,which will provide more accurate basic data and growth models for the identification of heterogeneity risk assessment of foodborne pathogens.The study of Vibrio parahaemolyticus growth heterogeneity will help us to explore the specificity of Vibrio parahaemolyticus strains of internal and external causes,so as to deal with more comprehensive assessment of Vibrio parahaemolyticus food safety risk.Therefore,the aim of this study is 1)to investigate the effects of temperature and salinity on the growth heterogeneity of 50 Vibrio parahaemolyticus strains,2)to study the effects of different sources on the growth variability of Vibrio parahaemolyticus,3)to explore the intrinsic effect of genotype on the growth of Vibrio parahaemolyticus,4)to study the effects of different media on the growth heterogeneity of Vibrio parahaemolyticus.The main research contents and research results are as follows: 1.Study on growth variability of Vibrio parahaemolyticus based on pure cultured mediumIn this study,50 strains of Vibrio parahaemolyticus from different sources and different genotypes were cultured in four temperature gradients(10 ?,20 ?,30 ?,37 ?)and 5 salinity gradients(0.5%,3%,5%,7%,9%),and their growth kinetics characteristics were evaluated.The growth curves of Vibrio parahaemolyticus were mapped by Bioscreen,and the maximum growth rate was calculated by modified Gompertz model.As two main environmental factors,the impacts of the temperature and salinity on the growth variability were not the same: The effect of low temperature on the decrease of the maximum growth rate?max is greater than that of high NaCl concentration.Therefore,the preserved food in the salty environment should be kept in the temperature below 10?,so that the Vibrio parahaemolyticus strain could be completely inactivated.The study also comfirmed that the combination of 37 ? and 3% sodium chloride concentration was the optimal growth condition of Vibrio parahaemolyticus.Further analysis of the coefficient of variation for the maximum growth rate ?max found that the strain growth variability increased as the growth conditions such as temperature and salinity in the activation range became more and more stressful.Comparing the classification of strains from different sources,the strain growth variability in freshwater aquaculture products was more obvious than that in marine aquaculture products.In addition,the experimental results showed that gene heterogeneity also affected the growth variability of Vibrio parahaemolyticus strains: growth heterogeneity of tlh+/tdh+/trh– genotype showed the greatest degree of change,and it was recommended that more attention should be given to the genotype of tlh+/tdh+/trh– associated with highly pathogenic and high growth heterogeneity in clinical food safety control.In conclusion,the findings of this study should be useful in incorporating strain variability in predictive microbiology and microbial risk assessment,and could provide scientific guidance for V.parahaemolyticus verification and prevention in nature as well as strain selection in experiments.2.The study on growth heterogeneity of Vibrio parahaemolyticus in salmonIn this experiment,three strains of Vibrio parahaemolyticus from freshwater,seawater and clinical respectively were collected and cultured in sterile salmon samples and stored at 6 different temperatures(4,7,10,15,25,30?).The growth curves were fitted by using the modified Gompetz growth model and the modified Baranyi inactivation model to obtain the growth kinetics parameters.The results showed that the temperature had a significant effect on the growth kinetics of Vibrio parahaemolyticus.The lower the temperature,the lower the growth rate was.The source also affected the growth variability of Vibrio parahaemolyticus,and the growth heterogeneity of freshwater strain was greater than that of seawater strain and patient strain.While the effect of temperature on the growth variability was higher than the effect of source.,The difference of the growth kinetics for 3 strains in the inactivated state were quite significant,which also showed that the worse the environment was,the greater the growth variability would be.This study emphasized the need for quantitative assessment of Vibrio parahaemolyticus in the inactivated state in the medium of salmon meat,which was helpful for the prevention of food safety risks in the actual production process.3.Comparison of growth heterogeneity of Vibrio parahaemolyticus in two different media(shrimp and salmon)In the first part of this study,the Vibrio strain samples ATCC 33847(tlh+/tdh+/trh–)at six temperature gradients(4 ?,7 ?,10 ?,15 ?,25 ?,30 ?)were cultured in the media of shrimp and salmon separately.The growth rate and lethal rate were calculated by using the modified Gompertz model and the modified Baranyi model respectively for the study of growth heterogeneity of Vibrio parahaemolyticus in different media.The results showed that the media had a significant effect on the growth variability of Vibrio parahaemolyticus.The worse the environment was,the greater the difference of growth variability of Vibrio parahaemolyticus in different media would be.In addition,the comparison of the lethal rates in the inactivated state revealed that the effect of temperature reduction on Vibrio parahaemolyticus cultured in salmon was weaker than that in shrimp.The second-order model of Belehradek equation was used to obtain the relationship between the media and the maximum specific growth rate as well as lag time of the strain respectively.It was shown that the strain cultured in shrimp grew faster than that in salmon,and the lag time performed shorter,suggesting that the risk of food safety caused by the growth of Vibrio parahaemolyticus in shrimp was greater than the risk in salmon.In the second part,two different strains of Vibrio parahaemolyticus were cultured in the media of shrimp and salmon separately.The growth of different strains within the same medium and the growth of the same strains in different media were compared.It was found that the effect of medium on the growth heterogeneity of Vibrio parahaemolyticus was greater than that of different strains.It also provided a theoretical basis and data support for the unified growth prediction model for multi-strain complex in the same environment to explore the risk assessment of microbes.