Safety Evaluation of a 405-nm LED Device for Direct Antimicrobial Treatment of the Murine Brain

Abstract

Antimicrobial resistance is a growing problem in human medicine that extends to biomedical research. Compared with chemical-based therapies, light-based therapies present an alternative to traditional pharmaceuticals and are less vulnerable to acquired bacterial resistance. Due to immunologic privilege and relative tissue sensitivity to topical antibiotics, the brain poses a unique set of difficulties with regard to antimicrobial therapy. This study focused on 405-nm 'true violet' light-which has been shown to kill multiple clinically relevant bacterial species in vitro yet leave mammalian cells unscathed-and its effect on the murine brain. We built a 405-nm LED array, validated its power and efficacy against a clinical bacterial isolate in vitro, and then, at the time of craniotomy, treated mice with various doses of 405-nm light (36, 45, and 54 J/cm²). The selected doses caused no behavioral derangements postoperatively or any observable brain pathology as determined postmortem by histologic evaluation and immunofluorescence staining for caspase 3 and glial fibrillary acidic protein, markers of apoptosis and necrosis. True-violet light devices may present an inexpensive refinement to current practices for maintaining open craniotomy sites or reducing bacterial loads in contaminated surgical sites.

Figure 1.

(A) Wavelength spectrum of visible light. (B) Properties of white light compared with laser and LED light. The monochromaticity of LED makes it a good candidate for directed therapy, despite a lack of coherence. Figure adapted from references 6 and 28, with permission.

Figure 2.

(A and B) Isoflurane-anesthetized mice receiving light treatment after craniotomy. (C) Drawing of the setup shown in panels A and B.

Figure 3.

Mean logarithmic decrease in the N:N_o ratio (no. of cfu after treatment: no. of cfu before treatment) of enumerated colony forming units of Enterobacter cloacae after 24-h incubation at 37 °C on tryptic soy agar after treatment in vitro with calculated doses of light. Error bars reflect 1 SD of log-transformed values.

Figure 4.

Coronal sections reveal no significant pathology in the mice euthanized at 1, 3, or 21 d after various doses of light treatment. Row and column headers refer to the treatment groups of the represented section. Each photomicrograph represents a different mouse. All sections are oriented at an angle, with the meninges along the diagonal from the lower-left to upper-right corner of the photograph. Cropped images were obtained from the area subjacent to the craniotomy site as confirmed at lower magnification. Hematoxylin and eosin stain; magnification, 10×.