ACE2 and infection: The fact that SARS-CoV-2 initially interacts with the mucosal epithelia associated with a complex microbiota (naso-oro-pharyngeal cavities) and that its mechanism of infection is related to the angiotensin-converting enzyme receptor 2 (ACE2), whose activity is influenced and, in turn, influences the microbiota of the upper respiratory and gastrointestinal tracts [1,2], suggests an implication of the microbiota in individual susceptibility to COVID-19 and in the severity of the infection [3,4].