Salivaricin E and abundant dextranase activity may contribute to the anti-cariogenic potential of the probiotic candidate Streptococcus salivarius JH.

Dental caries is an infectious disease that is continuing to increase in prevalence, reducing the quality of life for millions worldwide as well as causing considerable expense, with an estimated US$108 billion spent on dental care in the USA each year. Oral probiotics are now being investigated to determine whether they could play a role in the prevention and treatment of this disease. Streptococcus salivarius strain JH is a potential probiotic candidate that produces multiple proteinaceous antimicrobials (bacteriocins), the inhibitory spectrum of which includes Streptococcus mutans, one of the principal causative agents of dental caries. The genome of strain JH has previously been shown to contain the biosynthetic loci for the bacteriocins salivaricin A3, streptin and streptococcin SA-FF22. Here we show that strain JH also produces salivaricin E, a 32 aa lantibiotic with a mass of 3565.9 Da, which is responsible for the inhibition of S. mutans growth. In addition, strain JH was shown to produce dextranase, an enzyme that hydrolyses (1 → 6)-α-D-glucosidic linkages, at levels higher than any other S. salivarius tested. In vitro testing showed that partial hydrolysis of the exopolymeric substances of S. mutans, using strain JH dextranase, improved the anti-S. mutans inhibitory activity of the lytic bacteriocin, zoocin A. The multiple bacteriocin and dextranase activities of strain JH support its candidature for development as an oral probiotic.

Production of the lantibiotic salivaricin A and its variants by oral streptococci and use of a specific induction assay to detect their presence in human saliva.

Salivaricin A (SalA), the first Streptococcus salivarius lantibiotic to be characterized, appears to be inhibitory to most Streptococcus pyogenes strains. A variant of the SalA structural gene (salA1) is present in more than 90% of S. pyogenes strains, but only strains of M serotype 4 and T pattern 4 produce the biologically active peptide. The present study identifies four additional variants (salA2 to salA5) of the SalA structural gene and demonstrates that each of the corresponding inhibitory peptides (SalA2 to SalA5) is produced in vitro. These variants appear to be similar to SalA and SalA1 in their inhibitory activity against Micrococcus luteus and in their ability to act as inducers of SalA production. It had previously been shown that S. pyogenes strain SF370 had a deletion (of approximately 2.5 kb) in the salM and salT genes of the salA1 locus. In the present study, several additional characteristic deletions within the salA1 loci were identified. S. pyogenes strains of the same M serotype all share the same salA1 locus structure. Since S. salivarius is a predominant member of the normal oral flora of healthy humans, strains producing anti-S. pyogenes lantibiotics, such as SalA, may have excellent potential for use as oral probiotics. In the present study, we have used a highly specific SalA induction system to directly detect the presence of SalA in the saliva of humans who either naturally harbor populations of SalA-producing S. salivarius or who have been colonized with the SalA2-producing probiotic S. salivarius K12.