Establishment of Defined Mixed Bacterial Plaques on Teeth in a Laboratory Microcosm (Model Mouth)

Abstract

Actinomyces viscosus WVU627, ‘ Streptococcus mitior ’ LPA-1 and Veillonella alcalescens OMZ193 were grown in pure or mixed culture on teeth in a model mouth which was supplied with synthetic saliva and an intermittent nutrient supplement containing 1 per cent (w/v) glucose. All organisms became established in pure culture although V. alcalescens colonised very poorly unless 1 per cent (w/v) lactate was supplied in place of the glucose. Mixed cultures of all three organisms were readily estabiished. In general, numbers and proportions of species varied widely in mixed culture, but were comparable to those observed in human dental plaque studies. When grown in association with A. viscosus and ‘ S. mitior ’, V. alcalescens achieved similar numbers to pure cultures supplied with lactate, thus demonstrating that a food chain existed. Higher viable counts of ‘ S. mitior ’ were obtained from mixed plaques, compared with pure cultures. However, less A. viscosus could be isolated when co-cultured with streptococci and veillonellae. Comparison of differential viable counts at 45 h, 66 hand 90 h after inoculation with these three organisms showed that both veillonellae and actinomycetes increased in numbers and proportions with incubation time. Streptococcus mutans C67-1 became established when inoculated together with the other organisms, although it attained lower numbers compared with pure cultures. It appeared that S. mutans antagonised A. viscosus and partially displaced this organism in mixed plaques which contained all four species. Keywords: Actinomyces viscosus ; ‘ Streptococcus mitior ’; Streptococcus mutans ; Veillonella alcalescens ; Model mouth; Microbial interactions.