Antiviral Effects of Quillaja saponaria Extracts Against Human Noroviral Surrogates.

Abstract

Aqueous extracts of Quillaja saponaria Molina are US FDA approved as food additives in beverages with known antiviral activity. Due to lack of commercially available vaccines against human noroviruses (HNoVs), alternate methods to prevent their spread and the subsequent emergence of variant strains are being researched. Furthermore, HNoVs are not yet culturable at high enough titers to determine inactivation, therefore surrogates continue to be used. This research analyzed the effect of aqueous Quillaja saponaria extracts (QE) against HNoV surrogates, Tulane virus (TV), murine norovirus (MNV-1), and feline calicivirus (FCV-F9) at room temperature (RT) and 37°C. Viruses (~ 5 log PFU/mL) were individually treated with 1:1 or 1:5 (v/v) diluted QE (pH ~ 3.75), malic acid control (pH 3.0) or phosphate-buffered saline (pH 7.2, as control) at 37°C or RT for up to 6h. Individual treatments were replicated three times using duplicate plaque assays for each treatment. FCV-F9 at ~ 5 log PFU/mL was not detectable after 15min by 1:1 QE at 37°C and RT. At RT, 1:5 QE lowered FCV-F9 titers by 2.05, 2.14 and 2.74 log PFU/mL after 0.5h, 1h and 2h, respectively. MNV-1 showed marginal reduction of < 1 log PFU/mL after 15min with 1:1 or 1:5 QE at 37°C without any significant reduction at RT, while TV titers decreased by 2.2 log PFU/mL after 30min and were undetectable after 3h at 37°C. Longer incubation with higher QE concentrations may be required for improved antiviral activity against MNV-1 and TV.