Characterizing the Adherence Profiles of Virulent Vibrio parahaemolyticus Isolates.

The human pathogen Vibrio parahaemolyticus is a leading cause of seafood-borne illness in the USA, and infections with V. parahaemolyticus typically result from eating raw or undercooked oysters. V. parahaemolyticus has been shown to be highly resistant to oyster depuration, suggesting that the bacterium possesses specific mechanisms or factors for colonizing oysters and persisting during depuration. In this study, we characterized eight different V. parahaemolyticus strains for differences in resistance to oyster depuration, biofilm formation, and motility. While each strain exhibited distinct phenotypes in the various assays, we determined that biofilm formation on abiotic surfaces, such as glass or plastic, does not directly correlate with bacterial retention in oysters during depuration. However, we did observe that the motility phenotype of a strain appeared to be a better indicator for persistence in the oyster. Further studies examining the molecular mechanisms underlying the observed colonization differences by these and other V. parahaemolyticus strains may provide beneficial insights into what critical factors are required for proficient colonization of the Pacific oyster.

Efficacy of low-temperature high hydrostatic pressure processing in inactivating Vibrio parahaemolyticus in culture suspension and oyster homogenate.

Culture suspensions of five clinical and five environmental Vibrio parahaemolyticus strains in 2% NaCl solution were subjected to high pressure processing (HPP) under various conditions (200-300MPa for 5 and 10 min at 1.5-20°C) to study differences in pressure resistance among the strains. The most pressure-resistant and pressure-sensitive strains were selected to investigate the effects of low temperatures (15, 5 and 1.5°C) on HPP (200 or 250MPa for 5 min) to inactivate V. parahaemolyticus in sterile oyster homogenates. Inactivation of V. parahaemolyticus cells in culture suspensions and oyster homogenates was greatly enhanced by lowering the processing temperature from 15 to 5 or 1.5°C. A treatment of oyster homogenates at 250MPa for 5 min at 5°C decreased the populations of V. parahaemolyticus by 6.2logCFU/g for strains 10290 and 100311Y11 and by >7.4logCFU/g for strain 10292. Decreasing the processing temperature of the same treatment to 1.5°C reduced all the V. parahaemolyticus strains inoculated to oyster homogenates to non-detectable (<10CFU/g) levels. Factors including pressure level, processing temperature and time all need to be considered for developing effective HPP for eliminating pathogens from foods. Further studies are needed to validate the efficacy of the HPP (250MPa for 5 min at 1.5°C) in inactivating V. parahaemolyticus cells in whole oysters.

Persistence of Vibrio parahaemolyticus in the Pacific oyster, Crassostrea gigas, is a multifactorial process involving pili and flagella but not type III secretion systems or phase variation.

Vibrio parahaemolyticus can resist oyster depuration, suggesting that it possesses specific factors for persistence. We show that type I pili, type IV pili, and both flagellar systems contribute to V. parahaemolyticus persistence in Pacific oysters whereas type III secretion systems and phase variation do not.

Reductions of Vibrio parahaemolyticus in Pacific oysters (Crassostrea gigas) by depuration at various temperatures.

Consumption of raw oysters has been linked to several outbreaks of Vibrio parahaemolyticus infection in the United States. This study investigated effects of ice storage and UV-sterilized seawater depuration at various temperatures on reducing V. parahaemolyticus in oysters. Raw Pacific oysters (Crassostrea gigas) were inoculated with a mixed culture of five clinical strains of V. parahaemolyticus (10290, 10292, 10293, BE 98-2029 and 027-1c1) at levels of 104⁻6 MPN/g. Inoculated oysters were either stored in ice or depurated in recirculating artificial seawater at 2, 3, 7, 10, 12.5, and 15 °C for 4-6 days. Holding oysters in ice or depuration of oysters in recirculating seawater at 2 or 3 °C for 4 days did not result in significant reductions (P > 0.05) of V. parahaemolyticus in the oysters. However, depuration at temperatures between 7 and 15 °C reduced V. parahaemolyticus populations in oysters by >3.0 log MPN/g after 5 days with no loss of oysters. Depuration at refrigerated temperatures (7-15 °C) can be applied as a post-harvest treatment for reducing V. parahaemolyticus in Pacific oysters.