Evaluation of 415-nm Blue Light and Hypochlorous Acid on the Rhesus Macaque (Macaca mulatta) Cranial Implant Microbiota

Cranially-implanted macaques are a crucial model for neuroscience research. Implant complications include abscesses, meningoencephalitis, and implant-tissue margin infections. Antimicrobial overuse has increased bacterial resistance, risking macaque health and complicating treatment of infections. This project aimed to assess the antimicrobial effects of blue light (∼415 nm) and hypochlorous acid (HOCl) treatment of cranial implant margins. Blue light exerts antibacterial effects via the induction of reactive oxygen species. We hypothesized that exposing cranial implant margins to a commercially available blue light device followed by HOCl treatment would improve clinical appearance and decrease bacterial burden as assessed by aerobic/anaerobic culture and tissue margin microbiota analysis (decreased α and β diversity and altered taxonomic composition). Eight rhesus macaques were exposed to 6 min of blue light followed by 0.024% HOCl solution three times weekly for 4 wk. Swabs for microbiota analysis and bacterial cultures were collected before and 24 h after the last treatment session. Control microbiota swabs were collected from a separate implant margin area only exposed to HOCl. All animals tolerated the blue light exposure but had varied improvement in margin clinical appearance. The most common bacteria identified on culture were Staphylococcus aureus (n = 8), β-hemolytic streptococcus (n = 8), and Corynebacterium ulcerans (n = 6). Microbiota analysis of the 16S rRNA V4 gene region demonstrated many anaerobic operational taxonomic units in addition to the aerobic species cultured, highlighting limitations of culture-based methods. All animals had unique microbiota taxonomic profiles with a mean of 84 operational taxonomic units and a median Shannon diversity index of ∼2.6. No significant differences were found between treatment groups, α diversity, or β diversity before and after the study. The effectiveness of blue light therapy likely relates to the device power and depth of penetration into the tissue margin. While safe, future work is needed to optimize the dose and delivery methods of light-based therapies.