Heat-Denatured Lysozyme Inactivates Murine Norovirus as a Surrogate Human Norovirus

Abstract

Human norovirus infects humans through the consumption of contaminated food, contact with the excrement or vomit of an infected person, and through airborne droplets that scatter the virus through the air. Being highly infectious and highly viable in the environment, inactivation of the norovirus requires a highly effective inactivating agent. In this study, we have discovered the thermal denaturing capacity of a lysozyme with known antimicrobial activity against gram-positive bacteria, as well as its inactivating effect on murine norovirus. This study is the first report on the norovirus-inactivating effects of a thermally denatured lysozyme. We observed that lysozymes heat-treated for 40 min at 100 °C caused a 4.5 log reduction in infectivity of norovirus. Transmission electron microscope analysis showed that virus particles exposed to thermally denatured lysozymes were expanded, compared to the virus before exposure. The amino acid sequence of the lysozyme was divided into three sections and the peptides of each artificially synthesised, in order to determine the region responsible for the inactivating effect. These results suggest that thermal denaturation of the lysozyme changes the protein structure, activating the region responsible for imparting an inactivating effect against the virus.

Inactivating Effect of Heat-Denatured Lysozyme on Murine Norovirus in Bread Fillings

“…Previous studies have confirmed that MNV-1 decreases by 4.5 log PFU/mL after exposure to heat-denatured lysozyme solution at 1 14) . Further, a sufficient inactivation effect was obtained with 1 heat-denatured lysozyme in vegetable salads 21) .…”

“…Heat-denatured lysozyme was prepared as previously described 14) . Egg-white lysozyme (Kewpie Corporation, Tokyo, Japan) was dissolved in distilled water at a concentration of 5 (w/v, pH 6.5±0.2) and filtered using a 0.20 μm filter.…”

“…reportedly show a norovirus-inactivating effect 22), 23) . Compared to these food-derived components, heat-denatured lysozyme can be considered to have a potent inactivating effect, since exposure to 1 heat- denatured lysozyme solution decreases MNV-1 by 4.5 log PFU/mL 14) . An advantage of using heat-denatured lysozyme as a viral inactivation agent is that it does not affect the flavor when added to food, because it is is flavorless and odorless 24) .…”

“…Normally, it is used as a protective enzyme against gram-positive bacteria, and it is also used in manufacturing drugs and food additives. Our previous study showed that heat-denatured lysozyme has an inactivating effect against norovirus 14) . In this study, therefore, we examined its inactivating effect against MNV-1 in bread fillings.…”

The influence of lysozyme and oligothiophenes on amyloid-β toxicity in models of Alzheimer’s disease

“…The mechanisms behind Aβ uptake is not known to date, but several receptors are believed to be implicated [239]. The reason for the decreased uptake could therefore be due to Aβ having an impaired ability to bind to the receptors when lysozyme is was previously reported that lysozyme has properties that goes beyond its enzyme activity, since inactivated lysozyme still possesses antimicrobial activity as well as the ability to neutralize murine norovirus [241]. Hence, lysozyme in itself could be important through other potential mechanisms than enzymatic activity.…”