Electrogenic Staphylococcus epidermidis Colonizes Nasal Cavities and Alleviates IL-6 Progression Induced by the SARS2-CoV Nucleocapsid Protein

Certain probiotic bacteria have been shown to possess an immunomodulatory effect and a protective effect on influenza infections. Using the Staphylococcus epidermidis K1 (S. epidermidis K1)-colonized mice model, we assessed the effect of nasal administration of glycerol or flavin mononucleotide (FMN) on the production of interleukin (IL)-6 mediated by the severe acute respiratory syndrome coronavirus 2 (SARS2-CoV) nucleocapsid protein (NPP). FMN, one of the key electron donors for the generation of electricity facilitated by S. epidermidis ATCC 12228, was detected in the glycerol fermentation medium. Compared to S. epidermidis ATCC 12228, the S. epidermidis K1 isolate showed significant expression of the electron transfer genes, including pyruvate dehydrogenase (pdh), riboflavin kinase (rk), 1,4-dihydroxy-2-naphthoate octaprenyltransferase (menA), and type II NADH: quinone oxidoreductase (ndh2). ICR mice were intranasally administered with S. epidermidis K1 with or without pre-treatment with riboflavin kinase inhibitors, then nasally treated with glycerol or FMN before inoculating the NPP. Furthermore, J774A.1 macrophages were exposed to NPP serum and then treated with NPP of SARS2-CoV. The IL-6 levels in the bronchoalveolar lavage fluid (BALF) of mice and macrophages were quantified using a mouse IL-6 enzyme-linked immunosorbent assay (ELISA) kit. Here, we report that nasal administration of NPP strongly elevates IL-6 levels in both BALF and J774A.1 macrophages. It is worth noting that NPP-neutralizing antibodies can decrease IL-6 levels in macrophages. The nasal administration of glycerol or FMN to S. epidermidis K1-colonized mice results in a reduction of NPP-induced IL-6 production.