Numerous plant compounds have antibacterial or
antiviral properties; however, limited research has been conducted with nonenveloped viruses. The efficacies of allspice oil,
lemongrass oil, and
citral were evaluated against the nonenveloped murine norovirus (MNV), a human norovirus surrogate. The
antiviral mechanisms of action were also examined using an
RNase I protection assay, a host cell binding assay, and transmission electron microscopy. All three antimicrobials produced significant reductions (P ≤ 0.05) in viral infectivity within 6 h of exposure (0.90 log10 to 1.88 log10). After 24 h, the reductions were 2.74, 3.00, and 3.41 log10 for
lemongrass oil,
citral, and allspice oil, respectively. The
antiviral effect of allspice oil was both time and concentration dependent; the effects of
lemongrass oil and
citral were time dependent. Based on the
RNase I assay, allspice oil appeared to act directly upon the viral capsid and
RNA. The capsids enlarged from ≤ 35 nm to up to 75 nm following treatment. MNV adsorption to host cells was not significantly affected. Alternatively, the capsid remained intact following exposure to
lemongrass oil and
citral, which appeared to coat the capsid, causing nonspecific and nonproductive binding to host cells that did not lead to successful
infection. Such contrasting effects between allspice oil and both
lemongrass oil and
citral suggest that though different plant compounds may yield similar reductions in virus infectivity, the mechanisms of inactivation may be highly varied and specific to the antimicrobial. This study demonstrates the
antiviral properties of allspice oil,
lemongrass oil, and
citral against MNV and thus indicates their potential as natural food and surface sanitizers to control noroviruses.