By Judith Fernandez-Piquer
Vibrio parahaemolyticus is a bacterial species indigenous to marine environments and can accumulate in oysters. Some V. parahaemolyticus strains are pathogenic and seafoodborne outbreaks are observed worldwide. This pathogen can reach infectious levels in oysters if post-harvest temperatures are not properly controlled. The aim of this thesis was to support oyster supply chain management by developing predictive microbiological tools to improve the safety and quality of oysters in the market. A predictive model was produced by injecting Pacific oysters (Crassostrea gigas) harvested in Tasmania with a cocktail of pathogenic and non-pathogenic V. parahaemolyticus strains, and measuring population changes over time at static storage temperatures from 4 to 30ºC. In parallel, the total viable bacteria count (TVC) model was measured.
The V. parahaemolyticus and TVC growth models were then evaluated with Pacific and Sydney Rock oysters (Saccostrea glomerata) harvested in New South Wales containing natural populations of V. parahaemolyticus. The model was developed into a software tool and evaluated in five different simulated oyster supply chains. Due to high uncertainty and variability associated with oyster supply chains a stochastic model which encompassed the operations from oyster farm to the consumer was built using ModelRisk® risk analysis software. The stochastic model may help the oyster industry evaluate the performance of oyster cold chains, and potentially enable real-time decisions if coupled with suitable traceability systems. It can also provide risk managers with valuable information about V. parahaemolyticus exposure levels.
Finally, in order to better understand microbial changes in oysters during distribution and storage, the dynamics of microbial communities in Pacific oysters was determined using 16S rRNA-based terminal restriction length polymorphism and clone library analyses. Significant differences in bacterial community composition were observed and the predominant bacteria were identified for fresh and stored oysters at different temperatures and storage temperature control and spoilage indicator organisms were identified.