Aggregation of Tulane Virus, a Human Norovirus Surrogate, Under Various Ionic Conditions: Implications in Thermal Tolerance

Abstract

Human norovirus is a major cause of foodborne illness worldwide, and the lack of a reliable cell culture system limits direct studies. Tulane virus has been used as a robust culturable human norovirus surrogate with similar capsid and genome structures; however, little is known about its particle size and zeta potential under varying ionic strengths and pH conditions, factors which are critical for understanding virus adsorption in food and environmental matrices and its fate when present in aggregated versus dispersed forms. This study investigated Tulane virus aggregation, zeta potential, and whether aggregation impacts virus thermal tolerance. Dynamic light scattering showed aggregation in 1 mM (pH 4.5) and 10 mM calcium chloride (pH 4.5–6.3), whereas 100 mM calcium chloride induced aggregation across a broader pH range (3.3–10), with all aggregation conditions occurring net surface charge approaches zero. Aggregation reduced countable infectious viral particles by ∼4 log10 PFU per ml, dependent upon aggregates size and number. Thermal tolerance of virus aggregates when held at 60 °C for 2 min was not significantly different from that of dispersed particles. These results indicate that the virus will readily aggregate under ionic conditions typical of food and environmental systems, providing important insights into the adsorption and stability of human norovirus surrogates.