Development of protocol for the effective detection of feline calicivirus as norovirus surrogate in oyster and lettuce

Foodbome illness caused by Noroviruses (NVs) is increasing rapidly in Korea. This study developed an effective detection protocol for NVs found in contaminated oysters and lettuce through an investigation using the major steps of virus particle separation, concentration and RT-PCR. As a surrogate model for NVs, the cultivable feline calicivirus (FCV) that belongs to the same Caliciviridae family was used. Instead of using a time-consuming ultracentrifugation method, efficient methods based on solvent extraction and PEG precipitation procedure were applied. Direct homogenization of a 25 g sample of whole oyster and lettuce in 175 mL PBS provided the simplicity that would be needed in the actual field of food product examination. The overnight PEG precipitation step at 4°C was reduced to 3 h by placing the reaction tube in ice and by adjusting the PEG concentrations. The application of the use of chloroform and 0.2 pm syringe filtration together showed a better detection efficiency than the use of chloroform alone in removing PCR inhibitors for both oyster and lettuce samples. Also, dilution of the extracted RNA solution before PCR provided increased sensitivity. The improved detection protocol developed in this study could be efficiently applied to detect FCV and most likely NVs from oysters and lettuce.