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. 2016 Jul 21;11(7):e0158835.
doi: 10.1371/journal.pone.0158835. eCollection 2016.

A Preliminary Study of the Effects of pH upon Fluorescence in Suspensions of Prevotella intermedia

Christopher K Hope  1   2 , Karen Billingsley  1   3 , Elbert de Josselin de Jong  1   4 , Susan M Higham  1   2
Affiliations

A Preliminary Study of the Effects of pH upon Fluorescence in Suspensions of Prevotella intermedia

Christopher K Hope et al. PLoS One. .

Abstract

The quantification of fluorescence in dental plaque is currently being developed as a diagnostic tool to help inform and improve oral health. The oral anaerobe Prevotella intermedia exhibits red fluorescence due to the accumulation of porphyrins. pH affects the fluorescence of abiotic preparations of porphyrins caused by changes in speciation between monomers, higher aggregates and dimers, but this phenomenon has not been demonstrated in bacteria. Fluorescence spectra were obtained from suspensions of P. intermedia that were adjusted to pHs commensurate with the range found within dental plaque. Two fluorescent motifs were identified; 410 nm excitation / 634 nm emission (peak A) and 398 nm excitation / 622 nm emission (peak B). A transition in the fluorescence spectra was observed from peak A to peak B with increasing pH which was also evident as culture age increased from 24 hours to 96 hours. In addition to these 'blue-shifts', the intensity of peak A increased with pH whilst decreasing with culture age from 24 to 96 hours. A bacterium's relationship with the local physiochemical environment at the time of image capture may therefore affect the quantification of dental plaque fluorescence.

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Conflict of interest statement

Competing Interests: Inspektor Research Systems BV provided the salary for author EdJdJ, but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. EdJdJ’s involvement in this research was under the auspices of his status as an honourary member of staff at The University of Liverpool. The specific role of EdJdJ is articulated in the ‘author contributions’ section. This does not alter the authors' adherence to PLOS ONE policies on sharing data and materials. EdJdJ holds several patents with respect to QLF technology. The remaining authors declared no conflict of interest.

Figures

Fig 1
Fig 1. Excitation emission matrices of suspensions of P. intermedia after 24 hours growth.
Adjusted to acidic (5.74), neutral (7.14) and alkaline (8.63) pHs. Peak A410:634 was predominant at acidic pH with a shoulder corresponding to peak B398:622 appearing at higher pHs.
Fig 2
Fig 2. Excitation emission matrices of suspensions of P. intermedia after 48 hours growth.
Adjusted to acidic (5.32), neutral (6.78) and alkaline (8.00) pHs. Peak A410:634 was predominant at acidic pH with shift towards peak B398:622 at higher pHs.
Fig 3
Fig 3. Excitation emission matrices of suspensions of P. intermedia after 72 hours growth.
Adjusted to acidic (5.36), neutral (6.98) and alkaline (7.84) pHs. Peak A410:634 was apparent at acidic pH with peak B398:622 becoming dominant at higher pHs.
Fig 4
Fig 4. Excitation emission matrices of suspensions of P. intermedia after 96 hours growth.
Adjusted to acidic (5.54), neutral (7.27) and alkaline (8.48) pHs. Peak A410:634 was apparent at acidic pH with peak B398:622 becoming dominant at higher pHs.
Fig 5
Fig 5. Fluorescence emission spectra at excitation wavelengths of 410 nm (Peak A) and 398 nm (Peak B) in suspensions of P. intermedia.
Spectra captured from different culture ages at ‘acidic’ (red), ‘neutral’ (green) and ‘alkaline’ (blue) pHs.
Fig 6
Fig 6. Excitation spectra at an emission wavelength of 634 nm in a 24 hour old suspension of P. intermedia.
Spectra focussing on the Q-bands at different pHs. Inset: Expanded view of the Q-band region.
Fig 7
Fig 7. Peak fluorescence values at different pH over time in suspensions of P. intermedia.
a) Peak A410:634. b) Peak B398:622. c) Ratio of Peak B398:622 / Peak A410:634.
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