Antimicrobial effects of blue light therapy against cutibacterium acnes: optimal dosing and impact of serial treatments

Eric J Cotter; Lisa M Cotter; Colleen N Riley; Jonah Dixon; Nicholas VanDerwerker; Aniekanabasi Ime Ufot; Jared Godfrey; David Gold; Scott J Hetzel; Nasia Safdar; Brian F Grogan

doi:10.1016/j.jseint.2023.11.020

Antimicrobial effects of blue light therapy against cutibacterium acnes: optimal dosing and impact of serial treatments

JSES Int. 2023 Dec 18;8(2):328-334. doi: 10.1016/j.jseint.2023.11.020. eCollection 2024 Mar.

Authors

Affiliations

¹ Department of Orthopedics and Rehabilitation, University of Wisconsin School of Medicine and Public Health, Madison, WI, USA.
² Department of Dermatology, University of Wisconsin School of Medicine and Public Health, Madison, WI, USA.
³ Division of Infectious Disease, Department of Medicine, University of Wisconsin School of Medicine and Public Health, Madison, WI, USA.
⁴ Department of Physics and Optics, University of Wisconsin-Madison, Madison, WI, USA.
⁵ Department of Biostatistics and Medical Informatics, University of Wisconsin-Madison, Madison, WI, USA.

Abstract

Background: Blue light therapy (BLT) is a Food and Drug Administration cleared modality used in dermatology as an effective treatment of acne. The primary purpose of this study is to determine if there are dose-dependent antimicrobial effects of BLT against Cutibacterium acnes (C. acnes).

Methods: A known strain of C. acnes was grown on chocolate agar in a controlled laboratory environment under anaerobic conditions for 1 week. After 1 week, 2-3 colonies of C. acnes were isolated and transferred to broth medium to incubate for 2 or 7 days. Broth vials (treatment arm) then underwent 1 of 6 different blue light dosing treatment regimens and a duplicate broth vial served as a control left open to the same environment. The BLT regimens were a single treatment of 25 J/cm², 50 J/cm², 75 J/cm², 100 J/cm², 2 serial treatments of 50 J/cm² separated by 24 hours, or 2 serial treatments of 75 J/cm² separated by 24 hours. The Omnilux Blue device (415 nm wavelength) was used for all BLT treatments and delivered, on average, 1.68 ± 0.004 J/min. Following treatment, the control and treatment broth samples were plated on chocolate agar and allowed to grow for 7 days. After 7 days, plates were counted and colony forming units (CFUs) were calculated. Six trials were completed for each BLT dosing regimen based on an a priori power analysis of 6 individual 2-sided t-tests. Comparisons in the primary outcome were made via mixed-effects analysis of variance with replicate as a random effect.

Results: All BLT treatment regimens resulted in significantly fewer CFUs than their aggregate control plate CFUs (P < .05 for all). Furthermore, in 2-way comparison of CFUs between BLT treatment groups, a single treatment of 75 J/cm² did lead to significantly less growth than 25 J/cm² (P = .017) and 50 J/cm² (P = .017). There were no improved antimicrobial effects with serial treatments when comparing 2 doses of 50 J/cm² with a single dose of 100J/cm², nor were 2 doses of 75 J/cm² more efficacious than 100 J/cm². Using the Omnilux Blue device, it took 44.8 minutes to deliver a 75 J/cm² dose.

Conclusion: BLT is an effective antimicrobial agent against this single virulent strain of C. acnes. Treatment dosing of 75 J/cm² was identified to be the most effective dose per unit time. Serial treatments did not lead to superior antimicrobial effects over a single, high-dose treatment.

Keywords: Blue light therapy; Culture; Cutibacterium acnes; Infection; Shoulder.