A possible probiotic (S. salivarius K12) approach to improve oral and lung microbiotas and raise defenses against SARS-CoV-2

Abstract: © LETTERS TO THE EDITOR © 2020 EDIZIONI MINERVA MEDICA Online version at http://www.minervamedica.it Minerva Medica 2020 June;111(3):281-3 DOI: 10.23736/S0026-4806.20.06570-2 A possible probiotic (S. salivarius K12) approach to improve oral and lung microbiotas and raise defenses against SARS-CoV-2 The coronavirus disease 2019 (COVID-19), a pathology caused by a novel beta-coronavirus named SARSCoV-2, is spreading rapidly and scientists are endeavoring worldwide to develop drugs for efficacious treatments and vaccines to protect human life. SARS-CoV-2 shares 79% sequence identity with SARS-CoV, the virus that caused a major outbreak in 2002-2003. In an identical manner to SARS-CoV, SARS-CoV-2 utilizes the ACE-2 receptor to bind to lung cells where it can cause severe, and possibly fatal, pneumonia. Most cases of transmission occur via person-to-person respiratory droplets and from environmental surfaces to the hands and then to the nose and mouth. Both pathways allow the virus to reach, as the first step, the upper respiratory tract from where it can spread to the lungs.1 The oral and the upper respiratory tract microbiotas contain large populations of the genus Streptococcus, with both commensal and pathogenic streptococci competing for several niches using a variety of strategies. For instance, streptococci have a remarkable ability to metabolize carbohydrates via fermentation, thereby generating acids as by-products. Excessive acidification of the oral environment by aciduric species such as Streptococcus mutans is directly associated with the development of dental caries. However, less acid-tolerant species such as Streptococcus salivarius can also produce large amounts of alkali, thereby playing an important role in the acid-base physiology of the oral cavity. Streptococcus salivarius is a numerically-prominent foundation member of the upper respiratory tract microbiota and some members of this species have been shown to exert a bacterial interference versus Streptococcus pyogenes, Streptococcus pneumoniae, Moraxella catarrhalis and Haemophilus influenzae, pathogens involved in recurrent pharyngitis, tonsillitis and in acute otitis media.2 A particular strain of Streptococcus salivarius, known as K12,3 has been clinically demonstrated to play a role in creating a stable upper respiratory tract microbiota capable of protecting the host from pathogenic bacte- Vol. 111 - No. 3 ria, fungi and viruses, thereby reducing the incidence of streptococcal pharyngo-tonsillitis, acute and secretory otitis media, halitosis, oral thrush and viral infections (rhinitis, influenza, pharyngitis, laryngitis, tracheitis and enteritis). The antibacterial role of strain K12 has been attributed to the release of bacteriocins (Salivaricin A2 and Salivaricin B) that can create instability in the membranes of susceptible, pathogenic bacteria. In contrast, the anti-Candida action seems to be mainly due to the ability of strain K12 to compete with fungal hyphae in adhering to oral mucosa. The proposed antiviral capability of strain K12 has been attributed to the observed development of an adaptive immune response as revealed by detection of enhanced levels of IFN-γ in human saliva 10 hours after oral lozenge administration, with values at 24 hours between 22 and 139 pg/ mL (Figure 1).4 Intrinsic antiviral activities are mediated by interferon-induced proteins and can cause the induction of nitric oxide synthase, which can directly impacts upon virus..