Inactivation of Human and Murine Norovirus by High-Pressure Processing

Abstract

The effect of high hydrostatic pressure (HPP) was evaluated for inactivation of murine norovirus (MNV), a propagable norovirus (NoV), and human NoV genogroup II.4. Inactivation of MNV was assessed by viral culturing (50% tissue culture infectious dose [TCID₅₀]) and real-time reverse-transcription–polymerase chain reaction (RT-qPCR), whereas NoV survival was determined only by RT-qPCR. A treatment of 450 MPa for 15 min at 45°C was sufficient to inactivate 6.5 log₁₀ of infectious MNV in culture medium as determined by TCID₅₀. Further, the inactivation of MNV was enhanced when pressure was applied at an initial temperature of 25°C. On the other hand, a baroprotective effect was observed when MNV suspensions were supplemented with 10 mM of CaCl₂. A 400 MPa treatment at 45°C inactivated >5 log₁₀ of infectious MNV, whereas the addition of CaCl₂ increased the pressure resistance of MNV, with <0.5 log₁₀ reduction observed. MNV decay as determined by TCID₅₀ was generally greater than that determined by RT-qPCR; for instance, MNV genomes were detected even after 15 min treatment at 450 MPa, with <0.5 log₁₀ reduction. Experiments with NoV suspensions showed that all tested HPP treatments reduced the numbers of NoV by <0.5 log₁₀ units as determined by RT-qPCR. Additionally, RNA of human NoV was more resistant to certain HPP treatments than the RNA of MNV.