Oral Administration of Limosilactobacillus reuteri KBL346 Ameliorates Influenza Virus A/PR8 Infection in Mouse

Influenza virus infection is an important public-health concern because of its high transmissibility and potential for severe complications. To mitigate the severity and complications of influenza, probiotics containing Lactobacillus are used and are generally recognized as safe. We evaluated the anti-influenza effect of Limosilactobacillus reuteri KBL346 in mice. BALB/c mice were orally administered live and heat-inactivated KBL346. After infection with influenza virus (A/Puerto Rico/8/34). KBL346 improved the body weight loss and the survival rate of mice infected with 4 times the LD 50 of influenza virus. Heat-inactivated KBL346 reduced the viral titer in the lungs and the plasma immunoglobulin G level. The expression levels of genes encoding inflammatory cytokines, such as interferon-? and toll-like receptor 2 (Tlr2), were decreased in the lung tissues of mice administered KBL346. Live and heat-inactivated KBL346 increased the expression level of Adamts4, which promotes recovery after infection, and decreased that of Tlr2. The a- and ß-diversities of the gut microbiome were modulated by the administration of KBL346. In addition, the structure of the gut microbial community differed according to the degree of weight loss. L. reuteri KBL346 has the potential to alleviate disease severity and improve histopathological changes in mice infected with influenza A/PR8, suggesting its efficacy as a probiotic against influenza infection.