Relationship of bacteriocin-like inhibitor production to the pigmentation and hemolytic activity of mutans streptococci.

An inhibitor production typing (P-typing) scheme originally devised for hemolytic streptococci of Lancefield groups A-G has been successfully applied to 35 mutans streptococcus isolates recovered from plaque cultures of 60 Dunedin schoolchildren. Thirteen different P-type designations were identified. Although 11 (31%) of the isolates failed to produce detectable inhibitory activity on the conventional blood agar medium used for P-typing, four of these isolates were inhibitor-positive on Trypticase Soy agar supplemented with 2% yeast extract and 0.5% calcium carbonate (TSYCa). Four mutans strains displayed strong beta-hemolysis on Columbia agar base containing human blood when incubated in a 5% CO2 in air atmosphere. Three of these also produced weak beta-hemolysis on sheep blood-supplemented medium and were further distinctive in that they were the only inhibitor P-type 767 strains to be detected in the present study. Five mutans isolates were pigment producers and this property seemed to occur independently of both the beta-hemolytic activity and the P-type designation. Upon testing an additional collection of 18 mutans strains of various serotypes, only seven (39%) were inhibitor-positive. However, three of the four serotype c strains were inhibitor producers. Two strains of serotype d and one of serotype g were more hemolytic on sheep than on human blood agar medium. In general, it seems that the most common human mutans streptococci (serotype c strains) are more likely than are other mutans strains to produce bacteriocin-like inhibitory activity and to be hemolytic for human rather than sheep erythrocytes.