Reduces Susceptibility to Secondary MRSA Infection in IAV-Infected Mice Through Promoting a T Cell-Independent IgA Response.

Secondary methicillin-resistant (MRSA) infection causes high mortality in patients with influenza A virus (IAV). Our previous study observed that the relative abundance of () was significantly reduced in both the respiratory tract and gut of IAV-infected mice and negatively correlated with the severity of IAV-MRSA coinfection pneumonia, but the role of remains unclear. Here, we supplemented the respiratory tract and gut of IAV-infected mice with live and performed a secondary MRSA infection challenge to investigate the effects and potential mechanisms further. Data showed that supplementation significantly reduced mortality and pathogen loads in IAV-MRSA coinfected mice and upregulated the lung T cell-independent (TI) IgA response in IAV-infected mice. The 16S rRNA gene sequencing results showed that supplementation ameliorated microbiota composition disorder and regulated metabolic dysfunction in the gut of IAV-infected mice. The correlation analysis and antibiotic cocktail treatment experiment showed that the TI IgA response in lungs is dependent on gut microbiota. These findings demonstrated that supplementation reduces susceptibility to secondary MRSA infection in IAV-infected mice by promoting the TI IgA response, and provide a new perspective on the use of probiotics to prevent secondary bacterial infection following IAV infection.