Enhanced Growth of Complex Communities of Dental Plaque Bacteria in Mucin-Limited Continuous Culture

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Abstract
The possibility that bacteria in plaque can grow at rates which are unaffected by the availability of dietary foods, because of their ability to metabolise salivary proteins, has been investigated by Keevil et al. using an in vitro continuous culture model. Plaque was collected aseptically from 13 school children, pooled and inoculated into a chemostat containing complex medium plus glucose. The principal genera enriched during growth at dilution rates of 005 and 0.2 h−1 (corresponding to mean generation times of 13.9 and 3.5 h, respectively, which might occur in vivo) were streptococci (including Streptococcus mutans) peptostreptococci, lactobacilli, fusiforms, veillonellae and Bacteroides spp. Addition of 0.1 per cent (w/v) mucin resulted in an increased growth yield, due to increases in the numbers of anaerobes, but the recovery of peptostreptococci and veillonellae decreased. Importantly, Actinomyces spp. increased and the appearance of spirochaetes was noted in all cultures fed with mucin. Withdrawal of glucose from mucin supplemented complex medium resulted in decreased growth yield, the loss of Neisseria spp. and decreased recovery of streptococci and lactobacilli. Replacement of the medium with artificial saliva containing 0.1 per cent (w/v) mucin enriched for Bacteroides spp., but lower numbers of the other genera found in plaque were also maintained at both growth rates. This suggests that the chemostat can be used successfully to model the oral ecosystem, with salivary proteins providing the principal source of carbon and nitrogen for growth.