Effect of microbial interaction on the colonization rate of Actinomyces viscosus or Streptococcus mutans in the dental plaque of rats

Abstract

The resident oral microflora of conventional Osborne-Mendel rats was challenged with A. viscosus or S. mutans strains. The adherence of the inoculated organism to the tooth surface and the subsequent growth were studied by means of viable counts determination. The initial growth rate of S. mutans in conventional rats was lower than in mono-associated gnotobiotic rats (doubing time, td = 5 h vs. td = 1.1 h). The delayed start of growth and the low initial growth rate indicated that a competitive interaction between S. mutans and the resident microflora occurred. The initial growth rate of A. viscosus in conventional rats (td = 3.1 h) was approximately the same as that in gnotobiotic rats (td = 2.8 h). The start of the growth of A. viscosus was only slighlty delayed compared with the start in gnotobiotic rats. Evidently, there is a neutralistic relationship between A. viscosus and the resident microflora. A. viscosus reached a stationary level .apprx. 7 days after inoculation; the S. mutans strains did not reach stationary levels until 2 wk after inoculation.