Effect of Blue Light and Photosensitizers on Cutibacterium acnes on Shoulder Periprosthetic Joint Infection Isolates

Abstract

Introduction: Cutibacterium acnes is gaining recognition as a leading pathogen after orthopaedic shoulder procedures. Photodynamic therapy, a combination of light and a photosensitizer, has demonstrated antimicrobial activity against C. acnes in the treatment of acne vulgaris. We sought to evaluate the effect of photodynamic therapy using blue light and photosensitizers on C. acnes isolates from shoulder prosthetic joint infections. Methods: C. acnes strains isolated from 19 patients with shoulder PJI were exposed to blue light alone (415 nm) or in combination with photosensitizers (fluorescein, riboflavin and demeclocycline). C. acnes strains were divided into 4 categories: Highly Sensitive (HS), Sensitive (S), Weakly Sensitive (WS), Resistant to blue light. Results: 13 of 19 C. acnes strains (68%) were S or HS to blue light alone. Of these 19 strains tested, 11 were tested with blue light and fluorescein or blue light plus riboflavin. Fluorescein (1 µg/mL) enhanced the effect of blue light in 6 of 11 strains (55%). Blue light plus riboflavin (10 µg/mL) resulted enhanced killing in 3 of 11 strains (27%), but produced a paradoxical photoprotective effect in 4 of 11 strains (36%), resulting in a net decrease compared to blue light alone. Demeclocycline, however, enhanced the effect of blue light in 16 of 17 strains (94 %). Conclusions: Blue light with the addition of photosensitizers killed C. acnes from periprosthetic shoulder infections in vitro, with demeclocycline having the most pronounced effect.

Keywords: Propionibacterium acnes; anaerobic pathogens; demeclocycline; fluorescein; riboflavin; shoulder infection.

Figure 1

Methods used for blue light killing of C. acnes. (A) Serial 10-fold dilutions of C. acnes were performed and plated on Brucella Blood Agar plates to estimate the number of C. acnes remaining viable. From top left, row 1 denotes C. acnes growth with 0 minutes i.e. no blue light exposure and subsequent rows denote growth after 15, 30 and 45 minutes of blue light exposure respectively. (B) Comparison between red and blue light in their ability to kill C. acnes showing that blue light was superior to red light in killing C. acnes. (C) Effect of culture turbidity on blue-light-induced killing of C. acnes strain TW37.

Figure 2

Susceptibility of C. acnes strains to blue light alone. (A) SN11 was killed by 15 minutes of exposure to blue light alone (HS). (B) Strain SN6 required a longer period of exposure to be killed by blue light alone (S). Strains (C) TW11 and (D) SN27 were not killed despite 60 minutes of blue light exposure (R).

Figure 3

Effect of fluorescein and blue light. (A) Strain TW37 was Sensitive after 45 min of exposure to blue light alone, but was eradicated after 30 minutes in the presence of fluorescein. (B) In the presence of fluorescein, the Resistant strain SN53 could be eradicated by blue light following 45 minutes of exposure. Strains (C) TW7 and (D) SN27 remained Resistant to the combination of blue light with fluorescein.

Figure 4

Effect of riboflavin and blue light. (A) The combination of blue light with riboflavin enhanced the killing of strain SN53, which statistically significant based on one tailed t-test analysis compared to blue light alone. (B) Riboflavin did not potentiate killing by blue light in strain TW12, a Resistant strain. In comparison, riboflavin had a protective effect on strains (C) TW37 and (D) TW58, preventing killing by blue light.

Figure 5

Effect of demeclocycline and blue light. (A) Strains SN14 and (B) SN53 became HS using blue light with demeclocycline. (C) Strain SN27, our most resistant strain, was WS using 1.5 µg/mL of demeclocycline with 45 minutes of blue light exposure. (D) Strain SN27 was S using 2.5 µg/mL of demeclocycline and was completely killed in 30 minutes in combination with blue light. *Statistically significant compared to blue light alone.