Commercially Available Citrus-based and Quillaja Extracts against Tulane Virus

Introduction: Human noroviruses cause a great number of gastrointestinal illnesses and deaths annually. In the absence of human norovirus vaccines, alternate preventive and control strategies are being studied. Tulane virus (TV) has been recognized as a novel cultivable surrogate to determine inactivation efficacy against human noroviruses. Natural plant components that contain bioflavonoids and organic acids (e.g., citric acid) and quillaja bark extracts (QE) that contain quillaic acid glycosides and saponins are known to have antimicrobial effects. QE has previously shown antiviral effects against Aichi virus. The application of these extracts against TV needs to be investigated.

Purpose: The objective of this study was to determine the effect of a commercially available citrus-based formula (CX) and quillaja bark extracts (QE) on the infectivity of TV at room temperature (RT).

Methods: TV (200µl) at 7 log PFU/ml was mixed with equal volumes of undiluted citrus-based antimicrobial (CX), quillaja extract (QE), or water (control) for 30, 60, 120 and 180 min at room temperature. After each time point, treatments were stopped in cell-culture media supplemented with 10% fetal bovine serum and serially diluted in cell-culture media supplemented with 2% fetal bovine serum. Infectivity was measured using standard plaque assays on confluent LLC-MK2 cells in 6-well plates in comparison to controls. Each treatment was replicated thrice and assayed in duplicate and data were statistically analyzed.

Results: Treatment with CX at RT resulted in TV reductions of 0.75±0.07, 1.04±0.24, 2.40±0.1, and 2.97±0.15 log PFU/ml after 30, 60, 120 and 180 min, respectively, while QE (50% diluted in water) showed only 0.98±0.10 log PFU/ml reduction after 180 min. 

Significance: The results indicate that the commercial citrus-based formulation is a promising alternate control strategy against TV. Further studies with CE using carrier tests and organic load against TV are needed for application as routine sanitizing washes.