Streptococcus salivarius is a commonly-occurring commensal bacterium found both exclusively and ubiquitously in the human oral cavity. The well-characterized S. salivarius strain K12 was originally selected for development as a probiotic on the basis of its particularly strong, megaplasmid-encoded inhibitory activity against the important disease- associated species Streptococcus pyogenes. As such, its initial application was to provide school-aged children with protection against streptococcal pharyngitis and its sequelae. More recently however a variety of additional health benefits have been linked to the regular use of probiotic preparations of strain K12. Reported benefits have included the reduction of acute otitis media episodes in young children and decreased severity of symptoms in halitosis-affected adults. We now report that the dosing of expectant mothers with strain K12 results in natural transmission of the probiotic bacteria to the mother’s baby in the first days of life. These observations, together with the previously-documented protection afforded by K12 against Streptococcus agalactiae vaginal infections in a mouse model provide a strong basis for further exploring the health benefits of perinatal applications of strain K12. Other studies conducted in Italian adults demonstrated an apparent protective effect of K12 dosing against upper respiratory tract virus infections and this has prompted us to investigate the anti-viral immuno-stimulatory activity of K12. A notable response detected has been the elevation of salivary levels of gamma interferon. In summary, a wide variety of potential and established beneficial health outcomes are now being linked to the use of probiotic S. salivarius strain K12.