Determining the spatial distribution of viable and nonviable bacteria in hydrated microcosm dental plaques by viability profiling.

The aim of this study was to use confocal laser scanning microscopy (CLSM) to examine the spatial distribution of both viable and nonviable bacteria within microcosm dental plaques grown in vitro. Previous in vivo studies have reported upon the distribution of viable bacteria only. Oral biofilms were grown on hydroxyapatite (HA) discs in a constant-depth film fermenter (CDFF) from a saliva inoculum. The biofilms were stained with the BacLight LIVE/DEAD system and examined by CLSM. Fluorescence intensity profiles through the depth of the biofilm showed an offset between the maximum viable intensity and the maximum nonviable intensity. Topographical differences between the surface properties of the viable and nonviable biofilm virtual surfaces were also measured. The profile of fluorescence intensity from viable and nonviable staining suggested that the upper layers of the biofilm contain proportionally more viable bacteria than the lower regions of the biofilm. Viability profiling records the transition from predominantly viable to nonviable bacteria through biofilms suggesting that this technique may be of use for quantifying the effects of antimicrobial compounds upon biofilms. The distribution of viable bacteria was similar to that found in dental plaque in vivo suggesting that the CDFF produces in vitro biofilms which are comparable to their in vivo counterparts in terms of the spatial distribution of viable bacteria.