Response of Vibrio parahaemolyticus Strains to High Hydrostatic Pressure Processing at Low Temperatures
Vibrio parahaemolyticus (Vp), a Gram-negative marine bacterium, is the leading cause of gastroenteritis in the United States through consumption of seafood, particularly oysters. High hydrostatic pressure processing (HPP) has been of great interest as a mean to eliminate Vp in live oysters. In this study, we examined the sensitivity of environmental Vp isolates (from oysters) and clinical Vp strains (10290, 10292, 10293, BE 98-2029 and 027-1c1) in 2% NaCl solution to pressure treatments (200 and 250 MPa for 5 min) at cold temperatures (5 and 15°C). Viable Vp counts were determined by spread plate method using trypticase soy agar containing 2% NaCl. Reductions of all environmental strains pressurized at 200 MPa at 15 °C were not significantly different from those observed at 5 °C while viability loss in clinical strains significantly increased in all strains, except 10290, after the process at 5 °C. Greater reductions were observed in environmental (4.2 to 5.3 log) and clinical strains (4.0 to 6.2 log) subjected to higher pressure of 250 MPa at 15°C. Significant increases in those reductions were observed in all tested strains when lowering the temperature to 5 °C (P < 0.05). Some environmental strains were more pressure-resistant than clinical strains. Efficacy of HPP in inactivating Vp cells was enhanced by lower operation temperature from 15 to 5 °C. Understanding the difference in pressure resistance among strains is important to establish processing parameters to ensure safety of pressure-treated oysters.