Modeling shifts in microbial populations associated with health or disease

Abstract

Stable microbial communities associated with health can be disrupted by altered environmental conditions. Periodontal diseases are associated with changes in the resident oral microflora. For example, as gingivitis develops, a key change in the microbial composition of dental plaque is the ascendancy of Actinomyces spp. and gram-negative rods at the expense of Streptococcus spp. We describe the use of an in vitro model to replicate this population shift, first with a dual-species model (Actinomyces naeslundii and Streptococcus sobrinus) and then using a microcosm model of dental plaque. The population shift was induced by environmental changes associated with gingivitis, first by the addition of artificial gingival crevicular fluid and then by a switch to a microaerophilic atmosphere. In addition to the observed population shifts, confocal laser scanning microscopy also revealed structural changes and differences in the distribution of viable and nonviable bacteria associated with the change in environmental conditions. This model provides an appropriate system for the further understanding of microbial population shifts associated with gingivitis and for the testing of, for example, antimicrobial agents.

FIG. 1.

Species counts in dual-species biofilms. ⧫, A. naeslundii; ▵, S. sobrinus. Solid lines represent runs in which artificial GCF addition and a switch to microaerophilic conditions were commenced on day 8. Dashed lines represent runs in which no change in conditions was implemented. Error bars represent the standard deviations (n = 4).

FIG. 2.

Species counts from microcosm biofilms when artificial GCF addition and a switch to microaerophilic conditions were commenced on day 7. ⧫, Actinomyces spp.; ▵, Streptococcus spp. Error bars represent the standard deviations (results combined from two separate CDFF experiments; n = 8).

FIG. 3.

Species counts from microcosm biofilms when artificial GCF and microaerophilic gas addition were commenced on day 14 and then ceased on day 28. ⧫, Actinomyces spp.; ▵, Streptococcus spp. Error bars represent the standard deviations (n = 5).

FIG. 4.

CLSM images (300 by 300 μm) of microcosm biofilms taken from 10-day-old biofilms before the addition of artificial GCF and microaerophilic gas (a) and from biofilms after the addition at day 24 (b) at a depth of 50 μm. Green represents viable bacteria, and red represents nonviable bacteria.

FIG. 5.

Normalized relative intensity values for fluorescence of viable and nonviable bacteria present through each layer of the biofilm. (a) Biofilms before the addition of artificial GCF and microaerophilic gas and (b) biofilms after the addition. ▪, viable bacteria; ⋄, nonviable bacteria.