The Ecology of Bacteriocin-producing Strains ofStreptococcus salivarius

Interest in bacteriocin-producing components of the human normal oral microbiota centres on their possible interference with colonisation by potentially pathogenic bacteria. Certain strains of Streptococcus salivarius produce bacteriocin-like agents displaying exceptional inhibitory activity toward Lancefield Group A streptococci. Four individuals were identified as naturally harbouring high proportions (> 90 per cent) of bacteriocin-producing strains of S. salivarius . Bacteriocinogenic isolates from three of these individuals and the previously described strain 20P3 displayed identical patterns of inhibition when tested by a deferred antagonism method against a series of ten indicator organisms. The fourth individual harboured S. salivarius strains producing a distinct, though possibly related, inhibitory pattern. All agents were of apparently low molecular weight (< 8000) and were stable to heating at 80°C for 30 min. The four individuals harbouring bacteriocinogenic S. salivarius strains possessed significantly greater proportions (p < 0.001) of bacteriocin-resistant Gram-positive alpha-haemolytic cocci than did 13 control individuals (not found to harbour bacteriocinogenic S. salivarius strains). These results accord with the idea that the production of active bacteriocins in situ should select a relatively bacteriocin-resistant accompanying microbiota. Keywords: Streptococcus salivarius ; Bacteriocin; Microbial interference; Indigenous microbiota; Colonisation resistance.