Evaluating the effect of local pH on fluorescence emissions from oral bacteria of the genusPrevotella

Abstract

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 AE 1 nm with a second emission peak developing with increasing pH at 622 nm. A linear relationship was demonstrated between pH and the log 10 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. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Spectral complexity of 5-ALA induced PpIX fluorescence in guided surgery: a clinical study towards the discrimination of healthy tissue and margin boundaries in high and low grade gliomas

“…Then, it is consistent with the shift from high to low density in our study, which was 4 nm. The presence of a second peak of fluorescence at 620 nm, which produces this shift, has been shown in tissues [32,[39][40][41] or in cell culture [42,43]. It is known that such a shift can be induced by a change in PpIX aggregation, which modifies the proportions in State 634 and State 620 of PpIX [35][36][37][38].…”

“…But its origin in vivo is still an open issue. Some works support the assumption that the origin of the peak at 620 nm in vivo is a different aggregate of PpIX [32,42]. Other works [39,43] explained it by precursors of uroporphyrins or coproporphyrins.…”

“…Furthermore, some results indicate that in ALA-induced and tumor conditions PpIX could spread outside the mitochondria and be partly sensitive to cytosolic microenvironment [51]-[53], or even to extracellular microenvironment [51]. Some works support the assumption that the origin of the peak at 620 nm in vivo is a different aggregate of PpIX [32,42]. Other works [39,43] explained it by precursors of uroporphyrins or coproporphyrins.…”

“…The presence of the second peak of fluorescence of PpIX at 620 nm is known in solution and closely linked with the chemical microenvironment [35][36][37][38]. This peak has been observed in tissues [32,[39][40][41] or in cell culture [42,43]. But its origin in vivo is still an open issue.…”

Nonlinear relation between concentration and fluorescence emission of protoporphyrin IX in calibrated phantoms

“…The pH of a fourth solution containing Intralipid, with a lipid volume fraction (LVF) of 6 ppm was changed in the pH range of 5 to 9 by minute addition of hydrochloric acid (HCl) or NaOH to study the influence of pH variations on PpIX emitted spectrum as proposed by Hope and Higham. 17 Concentration of each studied item was regularly increased and emitted fluorescence was measured each time. The maximum concentration was chosen to reach the asymptote of State620 contribution, i.e., when the overall shape of the fluorescence emission spectrum stabilizes with increasing concentration.…”