<jats:title>ABSTRACT</jats:title> <jats:p> The commercial probiotic <jats:italic>Streptococcus salivarius</jats:italic> strain K12 is the prototype of those <jats:italic>S. salivarius</jats:italic> strains that are the most strongly inhibitory in a standardized test of streptococcal bacteriocin production and has been shown to produce the 2,368-Da salivaricin A2 (SalA2) and the 2,740-Da salivaricin B (SboB) lantibiotics. The previously uncharacterized SboB belongs to the type AII class of lantibiotic bacteriocins and is encoded by an eight-gene cluster. The genetic loci encoding SalA2 and SboB in strain K12 have been fully characterized and are localized to nearly adjacent sites on pSsal-K12, a 190-kb megaplasmid. Of 61 strongly inhibitory strains of <jats:italic>S. salivarius</jats:italic> , 19 (31%) were positive for the <jats:italic>sboB</jats:italic> structural gene. All but one (strain NR) of these 19 strains were also positive for <jats:italic>salA2</jats:italic> , and in each of these cases of double positivity, the two loci were separated by fewer than 10 kb. This is the first report of a single streptococcus strain producing two distinct lantibiotics.