The effects of mutual interaction and host diet on the growth rates of the bacteria Actinomyces viscosus and Streptococcus mutans during colonization of tooth surfaces in di-associated gnotobiotic rats.

The bacteria were simultaneously inoculated into the mouths of germ-free rats. The maximum growth rates attained by Strep. mutans (doubling time td = 1.4 h) or A. viscosus (td = 2.7 h) were approximately the same as in mono-associated gnotobiotic rats [td = 1.1 and 2.8 h, respectively (Beckers and van der Hoeven, 1982a)]. The presence of glucose or sucrose did not affect the maximum growth rates. In starved rats, the accumulation of microorganisms tended to decline sooner, suggesting that the growth was limited by the availability of nutrients. No interaction between the two organisms was detected at the stage of initial adherence to the tooth surfaces or during the first 24 h of growth. After that, the increase of A. viscosus was retarded in the presence of Strep. mutans T2, but not with Strep. mutans OMZ176. The retardation was more pronounced in the rats fed on glucose than on sucrose. Yet, at 24 days after inoculation. A. viscosus had increased in the glucose more than in the sucrose group. Hence sucrose did not stimulate the accumulation of Strep. mutans more than glucose.