Effect of Fluorescence Photobiomodulation on Canine Progenitor Epidermal Keratinocytes With and Without Staphylococcus pseudintermedius Colonisation.

BACKGROUND: Fluorescence photobiomodulation (FPB) is a treatment for canine dermatitis, yet no studies exist assessing its effect on canine keratinocytes in vitro. OBJECTIVES: To determine: (i) the anti-inflammatory and antimicrobial effect of FPB on canine progenitor epidermal keratinocytes (CPEK) with and without colonisation by Staphylococcus pseudintermedius (SP); (ii) changes in CPEK viability following FPB exposure; and (iii) SP colony count following FPB exposure. MATERIALS AND METHODS: Keratinocytes were grown in chamber slides, with and without SP, and treated with two, 2 min exposures to FPB. Supernatant was collected at 0, 1, 6, and 24 h post-FPB to evaluate cytokines (interleukin [IL]-2, IL-6, IL-7, IL-8, IL-10, IL-15, IL-18, interferon-γ induced protein 10 [IP-10], tumour necrosis factor-α, interferon-γ, keratinocyte chemotactic-like, granulocyte-macrophage colony-stimulating factor, and monocyte chemoattractant protein-1), and host defence peptides (β-defensin 3-like and cathelicidin) secretion. Cell cytotoxicity was assessed via lactate dehydrogenase and adenosine triphosphate assays. The supernatant pellet was collected at 0 and 24 h, resuspended, and plated. Bacterial colonies were counted after 24 h of incubation. Experiments were performed in duplicate and repeated five times. RESULTS: At 6 h post-FPB, IP-10 fluorescence intensity was mildly yet significantly decreased in CPEK+SP (p = 0.04). No other statistically significant differences were found for cytokine, β-defensin, cathelicidin, or SP colony counts. A lack of cytotoxicity was observed post-FPB over a 24 h period. CONCLUSIONS AND CLINICAL RELEVANCE: Fluorescence photobiomodulation may have a mild anti-inflammatory effect on CPEKs colonised by SP in vitro based on the significant decrease in IP-10 production 6 h post-FBP exposure, yet does not affect CPEK cell viability.