Inactivation of a norovirus by high-pressure processing

Murine norovirus (strain MNV-1), a propagable norovirus, was evaluated for susceptibility to high-pressure processing. Experiments with virus stocks in Dulbecco's modified Eagle medium demonstrated that at room temperature (20 degrees C) the virus was inactivated over a pressure range of 350 to 450 MPa, with a 5-min, 450-MPa treatment being sufficient to inactivate 6.85 log(10) PFU of MNV-1. The inactivation of MNV-1 was enhanced when pressure was applied at an initial temperature of 5 degrees C; a 5-min pressure treatment of 350 MPa at 30 degrees C inactivated 1.15 log(10) PFU of virus, while the same treatment at 5 degrees C resulted in a reduction of 5.56 log(10) PFU. Evaluation of virus inactivation as a function of treatment times ranging from 0 to 150 s and 0 to 900 s at 5 degrees C and 20 degrees C, respectively, indicated that a decreasing rate of inactivation with time was consistent with Weibull or log-logistic inactivation kinetics. The inactivation of MNV-1 directly within oyster tissues was demonstrated; a 5-min, 400-MPa treatment at 5 degrees C was sufficient to inactivate 4.05 log(10) PFU. This work is the first demonstration that norovirus can be inactivated by high pressure and suggests good prospects for inactivation of nonpropagable human norovirus strains in foods.