Electrogenic Staphylococcus epidermidis colonizes nasal cavities and alleviates IL-6 progression induced by SARS-CoV-2 nucleocapsid phosphoprotein

The cytokine storm leads to acute respiratory distress syndrome (ARDS) and multi-organ dysfunction in COVID-19 cases. One of the major cytokines is IL-6, which is positively associated with the severity of the condition. In the present study, nasal inoculation of SARS-CoV-2 nucleocapsid phosphoprotein (NPP) elevated IL-6 abundancy in bronchoalveolar lavage fluid (BALF) in mice. Staphylococcus epidermidis K1 ( S. epidermidis K1)-colonized mice nasally administered with glycerol or FMN resulted in a reduction of NPP-induced IL-6. S. epidermidis fermented glycerol to generate a large amount of electrons which further supported bacterial colonization. Inhibition of riboflavin kinase in S. epidermidis considerably suppressed the effect of nasal S. epidermidis plus glycerol on the decrement of NPP-induced IL-6. Taken together, our results show that nasal colonization of S. epidermidis mitigates a cytokine storm caused by SARS-CoV-2 infection.