Streptococcus salivarius is a commensal bacterium naturally present in the oral cavity and upper respiratory tract. Its use in the support or prevention of tonsillitis is primarily backed by scientific research, particularly regarding certain probiotic strains, most notably S. salivarius K12. Evidence suggests that this strain can inhibit the growth of pathogenic bacteria associated with tonsillitis, such as Streptococcus pyogenes, through the production of bacteriocins (antimicrobial peptides).

Several randomized controlled trials and observational studies have explored the efficacy of S. salivarius K12 in reducing the incidence and severity of recurrent pharyngotonsillitis, particularly in children. For instance, a 2009 study published in Annals of Otology, Rhinology & Laryngology demonstrated that regular administration of S. salivarius K12 significantly reduced episodes of streptococcal pharyngotonsillitis compared to placebo. Other studies have reported similar preventive effects, suggesting that colonization of the oropharyngeal mucosa by S. salivarius K12 may decrease the need for antibiotics and the frequency of infections.

However, while the data are promising, the number of high-quality, large-scale clinical trials remains limited, and most evidence pertains to prevention rather than treatment of active tonsillitis. The overall quality and consistency of the evidence justifies a moderate rating.