Abstract
A number of anaerobic oral bacteria, notably Prevotellaceae, exhibit red fluorescence when excited by short-wavelength visible light due to their accumulation of porphyrins, particularly protoporphyrin IX. pH affects the fluorescence of abiotic preparations of porphyrins due to transformations in speciation between monomers, higher aggregates, and dimers. To elucidate whether the porphyrin speciation phenomenon could be manifested within a microbiological system, suspensions of Prevotella intermedia and Prevotella nigrescens were examined by fluorescence spectrophotometry while being titrated against NaOH. The initial pH of the samples was <6, which was then raised toward the maximum found within a diseased periodontal pocket, being ∼pH 8.7. The intensity of the fluorescence emissions increased between 600 and 650 nm with increasing pH. Peak fluorescence emissions occurred at 635±1 nm with a second emission peak developing with increasing pH at 622 nm. A linear relationship was demonstrated between pH and the log10 ratio of 635:622 nm excitation fluorescence intensities. These findings suggest that the pH range found within the oral cavity could affect the fluorescence of oral bacteria in vivo, which may in turn have connotations for any clinical diagnoses that may be inferred from dental plaque fluorescence.
Highlights
Quantitative light-induced fluorescence-digital (QLF-D) is a photographic method of plaque assessment that is being developed to inform and improve oral health
The average increase in pH observed in the bacterial suspensions following the addition of a 0.5-μl aliquot of 50-mM NaOH was 0.26 Æ 0.07 for P. intermedia and 0.45 Æ 0.18 for P. nigrescens (Æ95% confidence intervals)
Prevotella spp. were chosen for these experiments since this genus produces relatively large amounts of protoporphyrin IX (PPIX) on the cell surface in the monomeric form[21] along other water-soluble porphyrins, such as coproporphyrin and uroporphyrin,[12] and because they fluoresce well under QLF-D lighting conditions when grown on blood-containing agars.[22]
Summary
Quantitative light-induced fluorescence-digital (QLF-D) is a photographic method of plaque assessment that is being developed to inform and improve oral health. QLF-D utilizes the intrinsic red fluorescence of a contingent of oral bacteria at 405 nm excitation produced by light-emitting diodes to visualize dental plaque.[1] Research is currently being undertaken to correlate plaque fluorescence with the progression of oral diseases, such as dental caries.[2,3,4,5] The three possible mechanisms by which changes in antecedent growth conditions and the local physicochemical environment (i.e., pH) could affect plaque’s fluorescent emissions are as follows. 1. By eliciting a shift in the composition of the microbial community[6] that would in turn alter the plaque metabolome and, the fluorophore complement of the plaque either directly or indirectly through mutual metabolic relationships.. By altering fluorophore metabolism/accumulation within individual bacteria.[8]
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