Strain typing of oral streptococci by the use of bacterial antagonism

Strain-typing methods utilizing microbial antagonism have been developed for S sanguis and for S mutans. The inhibition observed resembled that of bacteriocins. Inhibition within the species S sanguis was obtained with group D streptococci and facultative members of the genus Bacillus. Thirty-three inhibitors were paired (not in all possible combinations) with 37 isolates of S sanguis. Depending on the inhibitor, growth of between 15 and 85% of the sensitive indicators was halted. Three of the inhibitors manifested identical patterns of inhibition. Of the 37 S sanguis isolates, 34 exhibited individual patterns of inhibition. The three exceptions could be differentiated by their antagonism against sensitive indicators of S mutans. Variations in susceptibility to antagonism produced by group D streptococci allowed each of ten strains of S mutans to be typed. Present work for typing the oral streptococci is focused on computer-assisted searches for minimal typing sets. S mutans is sensitive to inhibition by some members of the species S sanguis. From a group of 58 challengers, 44 inhibited at least one of ten strains of S mutans, and 11 strains of S sanguis were able to halt the growth of half or more of the sensitive indicators. These results are useful not only for strain typing but form the basis for in vivo competition studies.