Pratten, Jonathan Richard; (1998) The effect of chlorhexidine and other antimicrobial agents on the formation and viability of oral bacterial biofilms. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Caries and periodontal diseases have been shown to stem from an imbalance in the normal oral microflora present on tooth surfaces as biofilms (plaque). There is considerable interest in developing chemical agents to supplement mechanical means (i.e. toothbrushing) of controlling these diseases. Although many studies have shown that planktonic oral bacteria can be easily killed by a range of available agents, such studies are largely irrelevant to the situation in vivo as the sessile (biofilm) forms of these bacteria are less susceptible to the action of such agents. The aims of this study, therefore, were to develop and test a laboratory model suitable for evaluating the effectiveness of antimicrobial agents against oral bacterial biofilms. A constant depth film fermentor was used to grow the biofilms. In order to mimic the situation in vivo, the biofilms were grown in an aerobic environment on a substratum similar to human enamel, with nutrients supplied by an artificial saliva. Initial studies were carried out using a mono-species (Streptococcus sanguis) biofilm grown on a variety of substrata and these were found to influence the susceptibility of the biofilms to various agents including chlorhexidine (CH), cetylpyridinium chloride and triclosan. The effectiveness of mouthwashes (containing different antimicrobial agents) against S. sanguis biofilms was then determined. The effect of CH on multi-species biofilms and microcosm plaques was also investigated. The reproducibility of the multi-species biofilms was poor, with varying proportions of species present in each run. The microcosm plaques were far more reproducible and the proportions of the predominant species were comparable with those found in supra-gingival plaque. The effects of a number of treatment regimes (involving CH) against these biofilms were investigated. When challenged with CH pulses there was an initial 2 log10 reduction in the number of viable organisms, however, although pulsing continued, the biofilms recovered in terms of both the viability and relative proportions of the constituent species. Cryosectioning of the microcosm plaques was carried out to determine the viability and proportions of species present at various depths throughout the biofilm. The CDFF proved to be a good method for reproducibly generating large numbers of bacterial biofilms comparable to supra-gingival plaque and enabled the evaluation of the activity of antimicrobial agents in a model which mimicked the situation in vivo.

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