Comparison Of Behavior Between Single And Mixed Vibrio Parahaemolyticus In Shrimp

Vibrio parahaemolyticus is recognized as the leading cause of human gastroenteritis associated with the consumption of seafood. Yearly, food safety incidents showed V. parahaemolyticus has now become the biggest threat to the quality of aquatic products. Therefore, it is good for shelf life by modeling the growth kinetics and studying its growth behavior of pathogenic and nonpathogenic V. parahaemolyticus in aquatic product. The main contents and results of this study are as follows:1. Comparison of growth characteristics of two highly pathogenic Vibrio parahaemolyticus at stress temperatureThe objective of this investigation was to compare the growth characteristics of highly pathogenic Vibrio parahaemolyticus at stress temperature on ready-to-eat shrimp ATCC 33847(tlh+/tdh+/trh-) and F 18(tlh+/tdh+/trh-) were inoculated on shrimp and stored at different temperatures(4~30 ℃). The growth models were chosen to fit the growth curves and were validated by the coefficient of determination(R2), Accuracy factor(Af) and bias factor(Bf). The growth parameters of V. parahaemolyticus from different sources were decided by maximum growth rate(μmax) and lag phase(LT). The result showed that big difference was existed between ATCC 33847 and F 18 from 4 ℃ to 15 ℃, while similar growth from 20 ℃ to 30 ℃. The modified Gompertz model was the optimal one to describe the growth of ATCC 33847 and F 18 at 15~30 ℃(R2 > 0.99) while Baranyi model was for ATCC 33847 at 4~7 ℃ and F 18 at 7 ℃. However, the optimal model for F 18 at 4 ℃ and 10 ℃ needed to be further studied. The difference value of μmax was 0.2 ~ 0.8 Log(cfu/m L)/h between ATCC 33847 and F 18 at 15~30 ℃, and the difference value of LT was 2.5~7 h. Compared the μmax with the ones of the published, significant difference(P < 0.05) could be found among the highly pathogenic, and the difference value become larger as the temperature becoming higher. Thus, large variability of V. parahaemolyticus could be found at stress temperature. What is more, the predictive models based on cocktail strains should be studied for more accurate risk assessment.2. Behavior of Vibrio parahemolyticus cocktail including pathogenic and nonpathogenic strains on cooked shrimpPathogenic Vibrio parahaemolyticus, an important foodborne bacterium, coexists with nonpathogenic strains of V. parahaemolyticus in the environment. However, current predictive models for V. parahaemolyticus usually focused on single strain without considering the pathogenic and nonpathogenic bacteria cocktail coexist situation. In this study, the behavior of four V. parahaemolyticus strains(F18:tlh+/ trh+/tdh-,ATCC17802:tlh+/ trh+/tdh-,F36:tlh+/ trh-/tdh-,ATCC33847:tlh+/ trh-/tdh+) and their cocktails on cooked shrimp were investigated at different temperatures(4, 7, 10, 15, 20, 25 and 30 oC). Total bacteria counts were enumerated by traditional plate count method, periodically. Results showed both V. parahaemolyticus cocktails and four single strains grew in a temperature range of 15- 30 oC and died at 4 to 7 oC. At 10 oC, for the cocktails, it inactivated at initial 100 hours and then grew rapidly; but for single strain, only one strain F18 displayed the similar growth tendency, while the others grew all the time. Compared with single strains, the primary and secondary model analysis showed that the cocktails displayed a better growth activity with higher maximum growth rate and shorter lag time. The above results indicated that modeling bacterial growth by using a cocktail of V. parahaemolyticus strains may be a better option for simulating growth in the real environment. This study will fill in the gap of predictive microbiology and improve significantly the accuracy of microbial risk assessment.3. Growth behavior of different genotypes of V. parahaemolyticus cocoktail by PMA multiplex real-time PCRA novel Taq Man-based multiplex real-time PCR method combined propidium monoazide treatment was firstly developed for the simultaneous quantification of different genotypes V. parahaemolyticus(F36:tlh+/ trh-/tdh-,ATCC33847:tlh+/ trh-/tdh+) in cooked shrimp. Baranyi model fitted the growth data and the result showed that the cocktail grew at 10 oC, andμmax of ATCC33847 was 3.559±0.666 Log(CFU/m L)/d, F36 was 2.999±0.415 Log(CFU/m L)/d. And the lagtime of ATCC33847 was 2.778±0.138 d, F36 was 2.826±0.146 d. The result showed that pathogenic bacteria in the cocktail grew better than the nonpathogenic bacteria, which provided trustworthly tool for risk assessment of the important pathogen.