TLR4 and COVID-19: Leptotrichia could produce lipopolysaccharides (LPS).[20] High level of LPS can induce the initiation of systemic proinflammatory phase by activating toll‐like receptors (TLR) such as TLR4, leading the release of cytokines, reactive oxygen species,[40] thereby mediating acute lung injury[41] and promoting COVID‐19 development.[42] Together, the increase of butyrate‐producing bacteria and the decrease of LPS‐producing bacteria, contribute to the recovery of SARS‐CoV‐2 infection.