Research
Monitoring and Identification of Vibrio parahaemolyticus
Problem: The safety of Alaska oysters has been challenged by the incidence of illnesses from Vibrio parahaemolyticus discovered in Alaskan oysters in 2004. This project seeks to determine the presence of the pathogen in oysters from three growing areas of Alaska.
Approach: The overall goal of this project is to determine the occurrence and presence of total and pathogenic V. parahaemolyticus in Alaska maricultured oysters. Our first objective is to use standard microbiological procedures to detect and confirm the identification of V. parahaemolyticus. A second objective is to use the modern laboratory technique of polymerase chain reaction (PCR) to rapidly test for the pathogenic species. A third objective is to determine if changing the harvest method by lowering the lantern nets containing the maricultured oysters into deeper and cooler waters can reduce pathogenic V. parahaemolyticus. The 4th objective is to determine cold-tolerance of V. parahaemolyticus isolates that may explain the presence of this bacterium in Alaskan waters.
Results: Four batches of Prince William Sound (PWS) oysters were obtained from the 2004 incident mariculture site during the summer of 2006. Oysters were split into two sub-batches: 1) half were sampled immediately for V. parahaemolyticus (Vp) and 2) half were held at room temperature for one day to simulate shipping and/or storage abuse before analysis for Vp. No Vp was found although other unidentified Vibrio species were isolated. The marine waters were colder (<13oC) than expected and may have prevented Vp from being present in PWS oysters. Training in using the polymerase chain reaction (PCR) from Dr. Yi-Cheng Su and his graduate student of Oregon State University occurred at FITC in spring 2006 in anticipation of positive cultures being isolated from Alaska oysters. The continued cold water temperatures hampered efforts to test oysters obtained from Southeast Alaska. During August 2007, only one batch was obtained and resulted in no Vp isolates. Likewise, the 2008 season maintained cold water temperatures with temperatures finally reaching 14oC by late August. Two batches of oysters from two locations at a Southeast Alaska oyster farm were subdivided and tested to increase the chances of finding Vp but to no avail. In late summer 2008, twenty-one Vp isolates were received from the food safety laboratory at the Alaska Department of Environmental Conservation (ADEC). These were from their 2005 stock cultures. The minimum growth temperature for these strains was not completed before the end of the project and will be continued in a post-project phase. In addition, water temperature monitoring will be expanded to various locations for establishing records at current and future Alaska oyster farms. These will be helpful for the oyster farmers for documenting water temperatures especially if a future case of Vp occurs. Temperature records will be necessary for determining which farms may be at risk from Vp. Prevention of illnesses to consumers from Vp will be mitigated by lowering the oyster holding nets to desirable temperatures (<13oC) for a specified time before harvesting, followed by chilling during distribution for sale.
Presentations & Publications: None
