Purpose: This study determined the time-dependent antiviral effects of myricetin and L-epicatechin at two concentrations on foodborne norovirus surrogate infectivity at 37°C.
Methods: The lab-culturable surrogates, feline calicivirus (FCV-F9) and murine norovirus (MNV-1) at titers of ~5 log PFU/ml were each individually mixed with equal volumes of myricetin or L-epicatechin at 0.5 and 1 mM for up to 2 h at 37°C. Treatments were neutralized in cell culture medium containing 10% fetal bovine serum, followed by serial dilution and plaque assays in duplicate and repeated thrice.
Results: FCV-F9 was found to be reduced to undetectable levels by myricetin at both concentrations, and decreased by 1.1 and 0.3 log PFU/ml with L-epicatechin at 0.5 and 0.25 mM (final concentration), respectively after 2 h. MNV-1 showed no significant titer reduction by myricetin or L-epicatechin at the two tested concentrations over 2 h. The antiviral effects of myricetin and L-epicatechin on FCV-F9 were found to be time-dependent. FCV-F9 was reduced by ~1.8 log PFU/ml upon immediate mixing with equal volume of 1 mM myricetin, further decreased by ~1.3 log PFU/ml within 1 h and to undetectable levels after 1.5 h at 37°C. In comparison to 0.5mM myricetin, L-epicatechin at 0.5mM decreased FCV-F9 titers by 0.3 log PFU/ml within 1 h and by ~ 1 log PFU/ml after 2 h at 37°C.
Significance: Our results indicate that the two plant-derived polyphenols at the tested concentrations appear to be effective only against FCV-F9 over 2 h at 37°C and not against MNV-1. Further studies using higher concentrations and longer incubation times may be necessary to determine any improved anti-noroviral effects and to understand their mechanism of action.