Predictive Models for the Effect of Storage Temperature on Vibrio parahaemolyticus Viability and Counts of Total Viable Bacteria in Pacific Oysters (Crassostrea gigas)

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Abstract
Vibrio parahaemolyticusis an indigenous bacterium of marine environments. It accumulates in oysters and may reach levels that cause human illness when postharvest temperatures are not properly controlled and oysters are consumed raw or undercooked. Predictive models were produced by injecting Pacific oysters (Crassostrea gigas) with a cocktail ofV. parahaemolyticusstrains, measuring viability rates at storage temperatures from 3.6 to 30.4°C, and fitting the data to a model to obtain parameter estimates. The models were evaluated with Pacific and Sydney Rock oysters (Saccostrea glomerata) containing natural populations ofV. parahaemolyticus. V. parahaemolyticusviability was measured by direct plating samples on thiosulfate-citrate-bile salts-sucrose (TCBS) agar for injected oysters and by most probable number (MPN)-PCR for oysters containing natural populations. In parallel, total viable bacterial counts (TVC) were measured by direct plating on marine agar. Growth/inactivation rates forV. parahaemolyticuswere −0.006, −0.004, −0.005, −0.003, 0.030, 0.075, 0.095, and 0.282 log10CFU/h at 3.6, 6.2, 9.6, 12.6, 18.4, 20.0, 25.7, and 30.4°C, respectively. The growth rates for TVC were 0.015, 0.023, 0.016, 0.048, 0.055, 0.071, 0.133, and 0.135 log10CFU/h at 3.6, 6.2, 9.3, 14.9, 18.4, 20.0, 25.7, and 30.4°C, respectively. Square root and Arrhenius-type secondary models were generated forV. parahaemolyticusgrowth and inactivation kinetic data, respectively. A square root model was produced for TVC growth. Evaluation studies showed that predictive growth forV. parahaemolyticusand TVC were “fail safe.” The models can assist oyster companies and regulators in implementing management strategies to minimizeV. parahaemolyticusrisk and enhancing product quality in supply chains.

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