Microbial Characteristics of Weissella cibaria HRL3 and Its Immunostimulatory Effects via TLR3/TLR9‐Dependent IFN‐α Production

Rhinacanthus nasutus (L.) Kurz is a medicinal plant whose roots, stems, and leaves are commonly used in tea and traditional Chinese medicine; however, the beneficial effects of its flowers remain to be investigated. In this study, the lactic acid bacteria (LAB) found in the flowers of R. nasutus (L.) Kurz were isolated using a medium containing fructose, which is abundant in the flowers, and their microbial characteristics were subsequently analyzed. The isolated LAB strain was identified as Weissella cibaria based on whole‐genome sequencing and was designated as HRL3. This strain was a facultative anaerobe whose growth was promoted under aerobic conditions, and it was classified as a heterofermentative LAB that produced lactate and ethanol via lactate fermentation. In addition, the HRL3 strain exhibited a unique carbohydrate utilization profile that differed from the type strain of W. cibaria . The immunostimulatory effects of the HRL3 strain were also investigated in this study. When added to mouse spleen cells, the HRL3 strain induced the production of IFN‐α, which is a cytokine that plays a key role in enhancing antiviral immune responses. This induction could occur through recognition by endosomal Toll‐like receptor (TLR) 3 and TLR9. Dectin‐1 may also contribute to IFN‐α production induced by the HRL3 strain. In an influenza A virus (IAV)‐infected mouse model, oral administration of the HRL3 strain was associated with increased IFN‐α mRNA expression, reduced IAV M mRNA expression, and attenuation of pulmonary histopathological changes. These findings provide new insights into the functional potential of R. nasutus (L.) Kurz flowers and the immunomodulatory activity of the HRL3 strain.