The role of respiratory microbiota in the protection against viral diseases: Respiratory commensal bacteria as next-generation probiotics for COVID-19

Abstract

On March 11, 2020, the World Health Organization declared a pandemic of coronavirusinfectious disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2(SARS-CoV-2) and imposed the biggest public health challenge for our civilization, with unforeseenimpacts in the subsequent years. Similar to other respiratory infections, COVID-19 is associated withsignificant changes in the composition of the upper respiratory tract microbiome. Studies have pointed to asignificant reduction of diversity and richness of the respiratory microbiota in COVID-19 patients.Furthermore, it has been suggested that Prevotella, Staphylococcus, and Streptococcus are associated withsevere COVID-19 cases, while Dolosigranulum and Corynebacterium are significantly more abundant inasymptomatic subjects or with mild disease. These results have stimulated the search for newmicroorganisms from the respiratory microbiota with probiotic properties that could alleviate symptomsand even help in the fight against COVID-19. To date, the potential positive effects of probiotics in thecontext of SARS-CoV-2 infection and COVID-19 pandemics have been extrapolated from studies carriedout with other viral pathogens, such as influenza virus and respiratory syncytial virus. However, scientificevidence has started to emerge demonstrating the capacity of immunomodulatory bacteria to beneficiallyinfluence the resistance against SARS-CoV-2 infection. Here we review the scientific knowledge regardingthe role of the respiratory microbiota in viral infections in general and in the infection caused bySARS-CoV-2 in particular. In addition, the scientific work that supports the use of immunomodulatoryprobiotic microorganisms as beneficial tools to reduce the severity of respiratory viral infections is alsoreviewed. In particular, our recent studies that evaluated the role of immunomodulatory Dolosigranulumpigrum strains in the context of SARS-CoV-2 infection are highlighted