The Black Bug Myth: Selective photodestruction of pigmented pathogens

David M. Harris, Steven L. Jacques, Richard Darveau

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


Background and Objective: It is commonly believed that pigmented pathogens are selectively targeted by dental lasers. To test this notion optical diffuse reflection spectroscopy (DRS) was used to obtain absorption spectra for the periodontal pathogens, Porphyromonas gingivalis (Pg) and Prevotella intermedia (Pi). Materials and Methods: Spectra from 400 to 1,100 nm wavelengths of Pg colonies cultured with different concentrations of hemin were obtained to test the hypothesis that “visual pigmentation” predicts absorption of near-infrared (IR) dental laser energy. Ablation threshold at 1,064 nm [1] was measured for the pathogenic fungus, Candida albicans (Ca). Results: The hypothesis was demonstrated to be true at 810 nm, it was false at 1,064 nm. Diode laser (810 nm) efficacy and “depth of kill” is dependent on hemin availability from 400 to about 900 nm. Pg and Pi absorption at 1,064 nm (µa = 7.7 ± 2.6 cm−1) is independent of hemin availability but is determined by another unknown chromophore. Ca is non-pigmented but very sensitive to 1,064 nm irradiation. Conclusions: The amount of visual pigmentation does not necessarily predict sensitivity to dental laser irradiation. Spectra in visible and near-IR wavelengths demonstrate a large difference in absorption between soft tissue and Pg or Pi. This difference represents a host/pathogen differential sensitivity to laser irradiation, the basis for selective photoantisepsis. Lasers Surg. Med. 48:706–714, 2016.

Original languageEnglish (US)
Pages (from-to)706-714
Number of pages9
JournalLasers in Surgery and Medicine
Issue number7
StatePublished - Sep 1 2016


  • 810 nm diode
  • C. albicans (Ca)
  • P. gingivalis (Pg)
  • P. intermedia (Pi)
  • bacterial reduction
  • dental laser
  • periodontal pathogens
  • pulsed Nd:YAG
  • tissue spectroscopy

ASJC Scopus subject areas

  • Surgery
  • Dermatology


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