Accumulation of Streptococci on Teeth in a Laboratory Microcosm (Artificial Mouth)

The accumulation on teeth of three strains of oral bacteria, ‘Streptococcus mitior‘ LPA-1, Streptococcus mutans C67-1, and Streptococcus rattus BHT, was studied from 8 to 90 hours after inoculation. Direct and viable counts demonstrated that strains BHT and C67-1 accumulated more rapidly than strain LPA-1, with fastest growth during the first 16 hours (td8-16 h 3.6–4.8 h). In older cultures, S. mutans and S. rattus continued to accumulate and a high proportion of the cells were viable. In contrast, ‘S. mitior’ cultures contained many non-viable organisms, possibly due to hydrogen peroxide-induced death. When S. rattus was co-cultured with ‘S. mitior’ it was strongly inhibited during the first 24 hours, but increased in proportion after 66 and 90 hours. It was concluded that in the interaction between‘S. mitior’ and S. rattus during initial plaque development, a potentially rapid initial growth rate was of less importance than the ability to antagonise the other organism.