THE STREPTOCOCCAL BACTERIOCIN-LIKE INHIBITORY SUBSTANCE, ZOOCIN-A, REDUCES THE PROPORTION OF STREPTOCOCCUS-MUTANS IN AN ARTIFICIAL PLAQUE

This paper reports the characterisation of a bacteriocin-like inhibito ry substance (BLIS), zoocin A, produced by Streptococcus zooepidemicus strain 4881 that exhibits inhibitory activity against strains of S. m utans, S. sobrinus and S. cricetus. A study of the inhibitory activity of strain 4881 against 98 bacterial strains using a deferred antagoni sm procedure showed that S. mutans strains were relatively more sensit ive than were strains of S. salivarius and S. sanguis. Zoocin A was pu rified from the supernate fluid of chemically defined medium cultures of strain 4881. Purified zoocin A (a protein of estimated MW 30 000) r etained biological activity over a wide pH range (4-10), was sensitive to several proteolytic enzymes and was relatively stable at 37 degree s C but not at 60 degrees C. A triple-species (S. mutans, S. sanguis a nd Actinomyces viscosus) plaque model was used to test the ability of zoocin A to modify plaque composition. Brief (2 min) exposure of prefo rmed plaque to zoocin A resulted in a significant decrease in the prop ortion of S. mutans and this effect persisted for up to 20 h after tre atment.