Optimizing the bactericidal effect of pulsed blue light on Propionibacterium acnes - A correlative fluorescence spectroscopy study

Violet Vakunseh Bumah, Daniela Santos Masson-Meyers, William Tong, Chris Castel, Chukuka Samuel Enwemeka

Research output: Contribution to journalArticlepeer-review

18 Citations (Scopus)


Propionibacterium acnes infection is the eighth most prevalent disease, affecting 80% of people worldwide. Resistance to antibiotics has been on the rise; over 40% of acne infections now resist commonly used topical and oral anti-acnes antibiotics, making treatment difficult. In our effort to refine blue light as an alternative safe clinically effective treatment, we determined if 100% bacterial suppression is attainable at ultralow irradiances and radiant energies, and explored the relationship between bacterial suppression and fluorescence during treatment. P. acnes were irradiated in vitro repeatedly three times per day at 3- or 4-hour intervals over three or more days, using 3 or 5 J/cm2 radiant energy of 450 nm pulsed blue light (PBL) at irradiances as low as 2 mW/cm2. In another series of experiments, we measured changes in P. acnes fluorescence as bacteria were repeatedly irradiated at various radiant exposures over three to four days. Our results showed that (1) 33% PBL, applied three times per day at 3-hour intervals each day over a three-day period at 2 mW/cm2 irradiance and 5 J/cm2 radiant exposure, resulted in100% bacterial suppression (7 log10 reduction), (2) the absorbed 450 nm light caused P. acnes to fluoresce predominantly in the red spectrum, with the fluorescence diminishing correlatively as treatment was repeated at 3-hour intervals and rising significantly during long periods of no treatment, and (3) treatment at 3-hour intervals gave better results than treatment at 4-hour intervals.

Original languageEnglish
Article number111701
JournalJournal of Photochemistry and Photobiology B: Biology
Publication statusPublished - Jan 2020
Externally publishedYes


  • Antimicrobial therapy
  • Fluorescence spectroscopy
  • P. Acnes
  • Printed LEDs
  • Pulsed blue light

ASJC Scopus subject areas

  • Radiation
  • Radiological and Ultrasound Technology
  • Biophysics
  • Radiology, Nuclear Medicine and Imaging


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