Use electrolyzed water to reduce Vibrio contamination in raw oysters.

V. parahaemolyticus and V. vulnificus are pathogens commonly found in oysters. Consuming raw oysters contaminated with these pathogens can lead to the development of acute gastroenteritis with symptoms of diarrhea, vomiting and abdominal cramps.

Oregon State University scientists wanted to evaluate the potential application of electrolyzed oxidizing (EO) water as a post-harvest treatment for reducing V. parahaemolyticus and V. vulnificus contamination in oysters. EO water is effective against many microorganisms and has been attracting attention due to its environmental safety. The electrolysis of deionized water containing a low concentration of sodium chloride (0.1%) in an electrolysis chamber, where the anode and cathode electrodes are separated by a diaphragm, imparts strong bactericidal and virucidal properties to the water collected from the anode--EO water.

The researchers investigated the antibacterial activities of EO water against V. parahaemolyticus and V. vulnificus by mixing cultures of the bacteria with EO water containing 10 ppm to 50 ppm of chlorine. The scientists determined the ability of EO water to reduce levels of V. parahaemolyticus and V. vulnificus in oysters by holding inoculated oysters in EO water at room temperature. The EO water exhibited strong bactericidal activity against both V. parahaemolyticus and V. vulnificus. Populations of V. parahaemolyticus and V. vulnificus decreased rapidly from [10.sup.7] CFU per ml to less than 10 CFU per ml in EO water within 30 seconds--a greater than 6-log reduction.

Holding oysters inoculated with V. parahaemolyticus or V. vulnificus in EO water containing 30 ppm chlorine resulted in about a 1-log MPN per g reduction of both pathogens in less than 8 hours. But the acidic and chlorine-containing EO water created an unfavorable growth condition for oysters. Exposing oysters for more than 24 hours in EO water containing high levels of more than 30 ppm of chlorine could lead to the death of oysters.

It appears that EO water could be used as a post-harvest treatment to reduce Vibrio contamination in oysters. However, treatment should be limited to less than 8 hours to avoid killing the oysters.

Further information. Yi-Cheng Su, Oregon State University Seafood Laboratory, 2001 Marine Dr., Suite 253, Astoria, OR 97103; phone: [phone]; fax: [phone]; email: [e-mail].