| Vibrio parahaemolyticus is a Gram-negative and halophilic human pathogen thatoccurs naturally in marine or estuarine areas and is frequently isolated from aquaticproducts, including shrimp. V. parahaemolyticus can cause wound infections,septicemia, diarrhea, headache and acute gastroenteritis. This pathogen is considered tobe the leading cause of aquatic products-derived illness around the world. The majorityof infections are caused by consumption of contaminated undercooked orcross-contaminated cooked aquatic products. A better understanding of the riskassessmemt of V. parahaemolyticus is needed to support measures to the quality controlof aquatic products as aquatic products consumption becomes more popular. Thepresent study performed systematic research on three aspects, which are the researcheson fundamental data, case study and risk control of risk assessment of V.parahaemolyticus in aquatic products. Firstly, the variability of maximum specificgrowth rate of different V. parahaemolyticus strains was studied and the growthpredictive model of V. parahaemolyticus was established. Secondly, the risk assessmentof V. parahaemolyticus in aquatic products was performed based on the developedmodel in the present study, then taking the risk assessment as a tool to evaluate the riskreduction effect of the traditional flavouring on V. parahaemolyticus in aquatic products.The details are as follows:Part1: The variability of specific growth parameters of pathogenic andnon-pathogenic V. parahaemolyticus in broth and Litopenaeus vannamei1. The variation between the maximum specific growth rate of pathogenic andnon-pathogenic V. parahaemolyitcus in brothIn order to develop the determination method for the maximum specific growthrate （μmax） of Vibrio parahaemolyticus （V. parahaemolyticus） using the automoatedturbidimetric system Bioscreen and comparing the variability of μmaxof9different pathogenic and non-pathogenic V. parahaemolyticus strains in TSB （3%NaCl，pH8.0）under15,20and25°C, to provide basic data for quantitative risk assessment of V.parahaemolyticus. Applying Bioscreen to determine OD540of the serially decimallycultures and combing the logarithm of initial bacterial concentrations （log CFU/mL） ofwhich to calculate the μmaxof9strains under15,20and25°C. Under15,20and25°C,coefficient of variation is20.72%,17.5%and15.98%respectively. The variability ofμmaxbetween different V. parahaemolyticus strains increased as temperature decreasedand there is no apparent relation between the maximum specific growth rate of V.parahaemolyticus in TSB and the pathogenic genes of V. parahaemolyticus.2. The growth variability of six different pathogenic and non-pathogenic V.parahaemolyticus on Litopenaeus vannameiThe present research is to study the variability of maximum specific growth rate ofsix pathogenic and non pathogenic V. parahaemolyticus strains on shrimp under37°C.The V. parahaemolyticus counts on inoculated cooked shrimp （Litopenaeus vannamei）was enumerated. The maximum specific growth rate of pathogenic V. parahaemolyticus（pVp） and nonpathogenic V. parahaemolyticus （npVp） were obtained by fitting growthdata to the three-phase linear model. The maximum specific growth rate （μmax） of tdhgene positive （tdh+） pVp Vp2（tdh+/trh-）, Vp6（tdh+/trh-）, Vp16（tdh+/trh-） was1.54,1.68and1.2（log10CFU/g）·h-1respectively. The μmaxof trh gene positive （trh+） pVp Vp3（tdh-/trh+） and Vp19（tdh-/trh+） was0.9and1.41（log10CFU/g）·h-1respectively, Theμmaxof npVp Vp18（tdh-/trh-） was0.95（log10CFU/g）·h-1. It is revealed that tdh+pVpgrow faster than the npVp, but no relationship between the genotype and μmaxwas foundin the present study.3. The growth variability of three different pathogenic V. parahaemolyticus onLitopenaeus vannamei.In order to study the growth parameters differences of different pathogenic V.parahaemolyticus on Litopenaeus vannamei and other growth matrix （broth andsalmon）. The growth curve of ATCC33847, F13and Clinical V. parahaemolyticus strainCV on Litopenaeus vannamei under12and35°C was tested and the growth data wasfitted by different primary models to derive the growth parameters and to compare themwith similar researches. It was revealed that Baranyi model fit the growth data of threepVp well. By comparing with similar researches under12and35the μmaxof pVp CVserotype O3:K6on was higher than the μmaxof pVp in broth and salmon. Part2: The research and analysis on the fundamental data required in the riskassessment of V. parahaemolyticus in aquatic products1. Modeling the growth of pandemic V. parahaemolyticus O3:K6on LitopenaeusvannameiGrowth predictive model of pandemic V. parahaemolyticus O3:K6strain onLitopenaeus vannamei was developed and validated. The maximum specific growth rateof this pandemic O3:K6strain ranged from0.11to1.47（1/h） between12°C and40°C.A square root type model was then used to quantify the dependency between thespecific maximum growth rate and temperature and the temperature at which no growthwas observed was1.0°C.2. The contamination level analysis of V. parahaemolyticus in aquatic products inShanghai market between2008to2011The prevalence and concentration analysis of V. parahaemolyticus in aquaticproducts in Shanghai market shows that the mean prevalence of aquatic products inShanghai is10.58%, the shrimp shows the highest contamination level among variousaquatic products, which is3.65MPN/g. It’s revealed that it should be paid moreattention to shrimp, wholesale aquatic products market and the May to October.Part3: The case study about quantitative microbial risk assessment of V.parahaemolyticus in aquatic products1. Quantitative microbial risk assessment of V. parahaemolyticus in aquaticproducts applying the predictive model constructed in the present studyThe research in former chapters, the predictive growth model for Vibrioparahaemolyticus in shrimp and the prevalence and concentration data of Vibrioparahaemolyticus in aquatic products in Shanghai market, were applied in the riskassessment. It’s shown that there are1823people will suffer from V. parahamolyticus inaquatic products in Shanghai per year. Among various factors affecting the risk of V.parahaemoyticus, the rank is as follows: the contamination level of Vibrioparahaemolyticus in aquatic products> the ratio of raw/not raw eaten for aquaticproducts> storage temperature> storage time> servings of aquatic products consumedby Shanghai citizen per year.2. Quantitative microbial risk assessment of V. parahaemolyticus in aquaticproducts applying the predictive model and parameters used in the FAO/WHO reportThe result derived from the model and parameters from FAO/WHO report are as follows: It’s shown that there are868people will suffer from V. parahamolyticus inaquatic products in Shanghai per year. Among various factors affecting the risk of V.parahaemoyticus, the contamination level of V. parahamolyticus in aquatic products>the ratio of raw/not raw eaten for aquatic products> storage temperature> storagetime> the adjustment factor for maximum specific growth rate> servings of aquaticproducts consumed by Shanghai citizen per year> the amount of consumption perserving. Among this parameters, the adjustment factor for maximum specific growthrate and the amount of consumption per serving. show negative correlation to the risk.3. The comparative analysis of the risk assessment of V. parahamolyticus in aquaticproducts using the two different models, the one in the present study and the other onein FAO/WHO report.It is revealed from the comparative analysis of the risk assessment of V.parahamolyticus in aquatic products using the two different models, the one in thepresent study and the other one in FAO/WHO report that the number of illness inShanghai caused by V. parahamolyticus contaminated aquatic products is different. Theresult from the present model which is based on the Litopenaeus vannamei is higherthan the FAO/WHO model which is based on the oyster. It’s suggested that, at the pointof guaranteeing food safety, the model constructed in the present study should be usefulto be applied in performing more conservative risk assessment to assist in the foodsafety control measure formulation by regulators to protect people’s health and safety.The predictive model constructed based on local strain and aquatic products could bemore suitable to the situation of China to protect safety of aquatic products.Part4: The risk control of modified atmosphere packaging and seasoning on thepathogenic V. parahaemolyticus in aquatic products1. The effect of modified atmosphere packaging on pathogenic pandemic clone V.parahaemolyticus O3:K6on Litopenaeus vannameiThe aim of this chapter is to study the risk control effect of two modifiedatmosphere packaging on V. parahaemolyticus pandemic clone O3:K6on Litopenaeusvannamei under4°C. It’s showed that the risk of V. parahaemolyticus in the modifiedatmosphere package is still high.2. The risk reduction effect of vinegar and wine on V. parahaemolyticus in aquaticproductsApplying risk assessment as a tool to evaluate the risk reduction effect of vinegar and wine on V. parahaemolyticus in aquatic products. The white spirit shows the bestrisk reduction effect, which can only reduce41%（median）. Other vinegar or wine canreduce the risk the percentage of20%. It’s revealed that the common sense “drinkingwine and eating aquatic products” could guarantee the food safety with respect toaquatic products consumption is unscientific. It is suggested for consumers that theaquatic products should be cooked totally and avoid eating raw aquatic products. |
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