Purpose: This study aims to determine if viral attachment through an ELISA is a means to determine infectivity, using heat, high pressure, ozone and UV-treated murine norovirus (MNV) by correlating ELISA optical density results to plaque assay results for infectivity.
Methods: ELISA plates were coated with porcine gastric mucin (PGM) and untreated and heat-, HPP-, ozone- and UV-treated MNV was added followed by monoclonal anti-MNV antibody. Anti-IgG antibodies were detected by horseradish peroxidase conjugated goat anti-mouse IgG antibody. The average OD405 of MNV-containing wells were divided by negative control wells and expressed as the ‘P/N ratio’; values ≥ 2 were considered positive. Infectivity of MNV following treatments was determined using the plaque assay. Capsid integrity was determined by RNase treatment and subsequent RT-PCR. Positive control wells were coated with virus sample and negative controls included wells without antibody, virus, or PGM coating.
Results: Heat-treated viral attachment decreased significantly with decreasing viral infectivity. Heat treated the P/N ratios were 1.86 ± 0.28 and 1.83 ± 0.03, respectively, at 80 and 100 °C, and attachment was not considered to be positive. This correlated MNV inactivated beyond the limit of detection and the MNV capsid was not intact as shown by RNase treatment. HPP-, ozone- and UV-treatment of MNV had no significant difference in attachment from control untreated virus, and the P/N Ratio was ≥ 2 for all treatments where inactivation was beyond the limit of detection. The capsids of HPP-, ozone- and UV-inactivated MNV remained intact as determined by RNase treatment.
Significance: The relationship between attachment and infectivity varied for the different food processing treatments, whereby, heat-inactivated MNV was the only treatment where this relationship existed. This observation suggests that partial destruction of the viral capsid is necessary to observe any changes in viral attachment to host cell receptors.