Prunus mume Extract Inhibits SARS-CoV-2 and Influenza Virus Infection In Vitro by Directly Targeting Viral Particles

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and influenza virus are major respiratory pathogens associated with substantial morbidity and a risk of severe disease. However, the effectiveness of current vaccines and antiviral drugs is limited by viral mutations. Umeboshi, a traditional Japanese food prepared from pickled <i>Prunus mume</i>, is known for its health benefits; certain components of <i>P. mume</i> have exhibited antimicrobial properties. However, the efficacy of <i>P. mume</i> against SARS-CoV-2 and influenza virus remains unknown. We aimed to examine the antiviral activity of <i>P. mume</i> extracts against SARS-CoV-2 and influenza virus. Cytopathic effect (CPE) assays and reverse transcription-quantitative polymerase chain reaction (RT-qPCR) analyses with full-time treatment demonstrated that four extracts (PM2, PM3, PM4, and PM6) among eight tested inhibited the replication of both viruses. Subsequent time-of-addition assays, plaque assays, and transmission electron microscopy (TEM) confirmed that PM2 directly inactivated viral particles of both viruses by disrupting their structural integrity. Additional evaluations of virion integrity and infectivity suggested that the antiviral activity of PM2 may also involve mechanisms other than direct virion disruption. These findings suggest that <i>P. mume</i>-derived components exhibit direct antiviral activities against SARS-CoV-2 and influenza virus, supporting their potential development as antiviral agents or infection-preventive dietary products.