Antagonistic Substances Produced by Streptococci from Human Dental Plaque and Their Significance in Plaque Ecology

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Abstract
69 streptococcal strains were freshly isolated from human dental plaque and tested for production of antagonistic substances on solid and liquid media under anaerobic conditions. Various bacteria from oral and non-oral origin were used as indicators. Production of, and sensitivity to antagonistic substances appeared to be species-dependent characteristics. Many Streptococcus mutans strains were antagonistic against other oral streptococci and actinomyces. Many Streptococcus salivarius strains inhibited oral streptococci, but not actinomyces. Streptococcus sanguis strains were relatively inactive as producer of antagonistic substances. The production of antagonistic substances was dependent on nutrient limitation. In broth cultures activity could be detected only rarely. Most of the products of S. mutans and S. salivarius were sensitive to proteolytic and sometimes also to lipolytic enzymes. A study of interactions among 46 S. mutans and 71 S. sanguis strains showed that strains isolated from the same plaque sample were slightly less antagonistic to each other than strains from different sites. The role of bacteriocins in regulating dental plaque flora in vivo is discussed.

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