Stability of the resident microflora and the bacteriocinogeny of Streptococcus mutans as factors affecting its establishment in specific pathogen-free rats.

The outcome of the experimental implantation of Streptococcus mutans strains in humans and animals is unpredictable, and neither success nor failure can be explained. It seems logical to assume that, apart from dietary and host factors, the characteristics of the S. mutans strain involved and those of the resident plaque microflora are important in colonization. For example, previous work in this laboratory suggested that bacteriocin production accounts at least in part for the establishment of an invading bacterium in a microbial ecosystem. In the present study, a complex specific pathogen-free Ny plaque ecosystem was obtained by the inoculation of specific pathogen-free rats with Actinomyces viscosus Ny1 and S. sanguis Ny101, and the establishment of S. mutans in such rats was then examined. It was found that bacteriocinogenic (bac(+)) strains generally colonized in much higher proportions than non-bacteriocinogenic (bac(-)) strains. Moreover, the longer the delay in introducing S. mutans, the poorer was its establishment. Shortly after inoculation of strains Ny1 and Ny101, there is probably a transient state in which microbial equilibrium has not been reached, but later the specific pathogen-free Ny system attains a stable climax community which more strongly resists invaders. The ability of a number of S. mutans strains to establish in such a climax community was then examined, and it was found that bac(+) strains generally established at a higher level than did bac(-) strains. In summary, it was concluded that, although the bac(+) state is an important property in the successful invasion of a plaque by S. mutans, the stability of the resident microflora is also an important factor.