The Streptococcal Bacteriocin-like Inhibitory Substance, Zoocin A, Reduces the Proportion of Streptococcus mutans in an Artificial Plaque

Abstract

This paper reports the characterisation of a bacteriocin-like inhibitory substance (BLIS), zoocin A, produced by Streptococcus zooepidemicus strain 4881 that exhibits inhibitory activity against strains of S. mutans, S. sobrinus and S. cricetus. A study of the inhibitory activity of strain 4881 against 98 bacterial strains using a deferred antagonism procedure showed that S. mutans strains were relatively more sensitive than were strains of S. salivarius and S. sanguis. Zoocin A was purified from the supernate fluid of chemically defined medium cultures of strain 4881. Purified zoocin A (a protein of estimated MW 30 000) retained biological activity over a wide pH range (4–10), was sensitive to several proteolytic enzymes and was relatively stable at 37°C but not at 60°C. A triple-species (S. mutans, S. sanguis and Actinomyces viscosus) plaque model was used to test the ability of zoocin A to modify plaque composition. Brief (2 min) exposure of preformed plaque to zoocin A resulted in a significant decrease in the proportion of S. mutans and this effect persisted for up to 20 h after treatment.

Key Words:

• Streptococcus mutans
• bacteriocin
• plaque
• ecology
• caries