Relaying to Decrease the Concentration of Oyster-Associated Pathogens

Oysters experimentally contaminated with indicator bacteria, Salmonella and poliovirus were used in relaying studies designed to measure microbial elimination under a variety of environmental conditions. Two factors, level of microorganism in the oyster and temperature of the water, were important in determining the length of time necessary to purge the contaminating organisms. Oysters under physiological stress cleansed at a slower rate than did healthy oysters. Based on the expected level of pathogen contamination in naturally polluted oysters, healthy relaid oysters were capable of cleansing in a 7-d period provided the temperature was above 10°C. These results were verified by following the elimination of indicator bacteria and poliovirus in commercially relaid oysters. Fecal indicator bacteria and enteric pathogenic bacteria were eliminated at similar rates but fecal coliform levels did not correlate with virus elimination. Relaying waters may contain some indicator bacteria and this study suggested that fecal coliforms may not be useful as end-point indicators for this method of oyster purification.