Lactobacillus delbrueckii ssp. bulgaricus OLL1073R-1-derived exopolysaccharide suppresses murine norovirus replication by modulating innate immune response.

Norovirus is a major cause of foodborne acute gastroenteritis, yet effective strategies to prevent norovirus infection have not been established. Given that an exopolysaccharide (EPS) can be orally consumed as a dietary component, we evaluated its potential to suppress norovirus replication in vitro. Here, we tested the antiviral effect of EPS derived from Lactobacillus delbrueckii ssp. bulgaricus OLL1073R-1 (R-1 EPS) against murine norovirus (MNV) in vitro using the mouse macrophage-like cell line, RAW264.7. Post-infection treatment significantly reduced the viral load of MNV in culture supernatants. Microarray-based transcriptome analysis showed that R-1 EPS treatment modulated MNV-induced host transcriptional responses, promoting preferential engagement of interferon (IFN)-mediated antiviral and inflammatory pathways. Consistent with the microarray-based transcriptome analysis, expression analysis using ELISA and RT-qPCR indicated increased expression of IFN, IFN-stimulated genes, and proinflammatory cytokines in infected cells treated with R-1 EPS. The results suggest that R-1 EPS modulated host innate immune responses, such as type I IFN and proinflammatory cytokine responses, during MNV infection, which may contribute to antiviral activity. Our results provide mechanistic insights into the host-directed antiviral effect of microbial EPS.