Fitness of Vibrio parahaemolyticus in Seawaters at Different Oyster Harvesting Temperatures

Introduction:  Vibrio parahaemolyticus is a foodborne pathogen that presents ubiquitously in seawaters. In the United States, Vibrio illnesses were commonly associated with consuming raw or contaminated oysters. Over 50% of outbreaks of V. parahaemolyticus infections were reported during summer months.

Purpose:  The aim of this study was to investigate the fitness of V. parahaemolyticus in seawaters at 10°C and 30°C.

Methods:  Pathogenic V. parahaemolyticus with the tdh gene (ATCC 43996) was inoculated into sterile seawater and stored at 10°C and 30°C for 10 days. The fitness of V. parahaemolyticus was evaluated by plating surviving cells on thiosulphate-citrate-bile salts-sucrose (TCBS) agar once per day for 10 days at 10°C. At 30°C, V. parahaemolyticus was plated every two hours for the first 12 hours, then every four hours for the next 12 hours. On day 2, 3, 5, and 10, V. parahaemolyticus was plated once each day. The Baranyi function was used to establish the primary predictive models. Biofilm formation was measured by staining with crystal violet dye and read via Bio-Rad microplate reader.

Results:  The established predictive models showed that V. parahaemolyticus decreased from 5.25 log CFU/g to 2.67 log CFU/g at 10°C and increased at 30°C from 4.76 log CFU/g to 6.95 log CFU/g after 10 days, with a minimum inactivation rate or maximum growth rate of -0.697 log CFU/day and 0.392 log CFU/day, respectively. The V. parahaemolyticus in seawater at 30°C has a significantly higher relative capacity of biofilm formation than 10°C (P<0.05).

Significance:  Different fitness of V. parahaemolyticus in seawater at different oyster harvesting temperatures was seen. Further preventive control strategies, such as depuration, need to be evaluated to ensure the safety of raw oysters.