Abstract
Foodborne outbreaks caused by norovirus (NV) are increasing in Japan, however there is few cases that NV was detected from the suspicious causative food. Therefore, NV detection from various kinds of food including oysters have been investigated by many researchers. A bacterial cultivation process (A3T method) has been introduced into the standard protocol for NV detection. The A3T method is for removing contaminants derived from oysters. To simplify the process of the A3T method, we used a frozen bacterial culture in 15% glycerin. Next, we examined NV contamination in 102 commercialized oysters for both raw consumption and cooking by using a modified A3T method using 10% and 20% homogenates of oysters. NV RNAs were detected in 19 of 102 oyster samples by the modified A3T method, while no samples were detected by the standard method using a 10% homogenate. NV RNAs were also detected in 26 samples by the modified method using a 20% homogenate, whereas 3 NV positive samples failed to be detected when using a 10% homogenate. Results revealed that the modified A3T method using frozen bacterial culture is a practically useful method for detecting NV in oysters. Furthermore, the NV detection rate can be enhanced by using 20% homogenates of oysters. Moreover, the results suggest that NV contamination in oysters is more prevalent in our country than previously reported.
