Red fluorescent biofilm: the thick, the old, and the cariogenic.

BACKGROUND: Some dental plaque fluoresces red. The factors involved in this fluorescence are yet unknown. OBJECTIVE: The aim of this study was to assess systematically the effect of age, thickness, and cariogenicity on the extent of red fluorescence produced by in vitro microcosm biofilms. DESIGN: The effects of biofilm age and thickness on red fluorescence were tested in a constant depth film fermentor (CDFF) by growing biofilms of variable thicknesses that received a constant supply of defined mucin medium (DMM) and eight pulses of sucrose/day. The influence of cariogenicity on red fluorescence was tested by growing biofilm on dentin disks receiving DMM, supplemented with three or eight pulses of sucrose/day. The biofilms were analyzed at different time points after inoculation, up to 24 days. Emission spectra were measured using a fluorescence spectrophotometer (λexc405 nm) and the biofilms were photographed with a fluorescence camera. The composition of the biofilms was assessed using 454-pyrosequecing of the 16S rDNA gene. RESULTS: From day 7 onward, the biofilms emitted increasing intensities of red fluorescence as evidenced by the combined red fluorescence peaks. The red fluorescence intensity correlated with biofilm thickness but not in a linear way. Biofilm fluorescence also correlated with the imposed cariogenicity, evidenced by the induced dentin mineral loss. Increasing the biofilm age or increasing the sucrose pulsing frequency led to a shift in the microbial composition. These shifts in composition were accompanied by an increase in red fluorescence. CONCLUSIONS: The current study shows that a thicker, older, or more cariogenic biofilm results in a higher intensity of red fluorescence.

Effect of metalloporphyrins on red autofluorescence from oral bacteria.

The aim of this study was to assess the red autofluorescence from bacterial species related to dental caries and periodontitis in the presence of different nutrients in the growth medium. Bacteria were grown anaerobically on tryptic soy agar (TSA) supplemented with nutrients, including magnesium-porphyrins from spinach and iron-porphyrins from heme. The autofluorescence was then assessed at 405 nm excitation. On the TSA without additives, no autofluorescence was observed from any of the species tested. On the TSA containing sheep blood, red autofluorescence was observed only from Parvimonas micra. When the TSA was supplemented with blood, hemin, and vitamin K, red autofluorescence was observed from Actinomyces naeslundii, Bifidobacterium dentium, and Streptococcus mutans. Finally, on the TSA supplemented with spinach extract, red autofluorescence was observed from Aggregatibacter actinomycetemcomitans, A. naeslundii, Enterococcus faecalis, Fusobacterium nucleatum, Lactobacillus salivarius, S. mutans, and Veillonella parvula. We conclude that the bacteria related to dental caries and periodontal disease exhibit red autofluorescence. The autofluorescence characteristics of the tested strains depended on the nutrients present, such as metalloporphyrins, suggesting that the metabolic products of the oral biofilm could be responsible for red autofluorescence.