Ultraviolet-C light for treatment of Candida albicans burn infection in mice

Abstract

Burn patients are at high risk of invasive fungal infections, which are a leading cause of morbidity, mortality, and related expense exacerbated by the emergence of drug resistant fungal strains. In this study, we investigated the use of UVC light (254 nm) for the treatment of yeast Candida albicans infection in mouse third degree burns. In vitro studies demonstrated that UVC could selectively kill the pathogenic C. albicans compared with a normal mouse keratinocyte cell line in a light exposure dependent manner. A mouse model of chronic C. albicans infection in non-lethal third degree burns was developed. The C. albicans strain was stably transformed with a version of the Gaussia princeps luciferase gene that allowed real-time bioluminescence imaging of the progression of C. albicans infection. UVC treatment with a single exposure carried out on day 0 (30 min postinfection) gave an average 2.16-log(10)-unit (99.2%) loss of fungal luminescence when 2.92 J cm(-2) UVC had been delivered, while UVC 24 h postinfection gave 1.94-log(10)-unit (95.8%) reduction of fungal luminescence after 6.48 J cm(-2). Statistical analysis demonstrated that UVC treatment carried out on both day 0 and day 1 significantly reduced the fungal bioburden of infected burns. UVC was found to be superior to a topical antifungal drug, nystatin cream. UVC was tested on normal mouse skin and no gross damage was observed 24 h after 6.48 J cm(-2). DNA lesions (cyclobutane pyrimidine dimers) were observed by immunofluorescence in normal mouse skin immediately after a 6.48 J cm(-2) UVC exposure, but the lesions were extensively repaired at 24 h after UVC exposure.

© 2011 The Authors. Photochemistry and Photobiology © 2011 The American Society of Photobiology.

Figures

Figure 1

In vitro susceptibility to UVC of keratinocytes and C. albicans. Bars: Standard deviation.

Figure 2

In vivo linear correlation of C. albicans CFU extracted from tissue at necropsy to fungal bioluminescence from infected mouse burns.

Figure 3

A) Successive bioluminescence images captured daily for 12 days of a representative mouse burn infected with bioluminescent C. albicans. B) A representative bioluminescence image of a mouse burn immediately after the peel-off of its scab as well as the detached scab from the same mouse. C) –D) Representative periodic acid–Schiff (PAS)-stained histological sections of C. albicans infected mouse burns biopsied on day 1 and day 4 post-infection, respectively. Scale bars: 20 µm.

Figure 4

A) Dose-response of fungal luminescence from a representative mouse burn infected with C. albicans and treated with UVC exposure on day 1 (24 hour) post-infection. B) Dose-responses of mean fungal luminescence of the mouse burns infected with C. albicans and treated by use of a single UVC exposure on day 0 (30 min, n=11) and day 1 (24 hour, n=12) post-infection, respectively. C) Time courses of mean fungal luminescence from infected mouse burns treated with a single UVC exposure on day 0 (n=11), day 1 (n=12), daily application of nystatin cream from day 1 to day 6 (n=8), and no treatment (n=12), respectively. D) –G) Mean areas under the bioluminescence-time plots (in the two-dimensional coordinate system in panel C) representing the overall fungal bioburden of the mouse burns in different groups (day 0 UVC treatment vs. no treatment, p=0.003; day 1 UVC treatment vs. no treatment, p=0.004; day 0 treatment vs. day 1 treatment, p=0.006; day 1 UVC treatment vs. daily treatment with nystatin cream, p=0.028).

Figure 5

A)–C) Morphologies of a representative mouse skin before, immediately after, and 24 hour after being exposed to UVC at a dose of 6.48 J/cm2, respectively. D) –F) Representative immuno-fluorescence micrographs of cyclobutane pyrimidine dimers (CPDs) in skin cell nuclei. G) –I) Micrographs of DAPI counterstaining of cell nuclei. J)–L) Micrographs of Masson’s trichrome stained sections. Biopsies were taken before (D, G, J), immediately after (E, H, K), and 24 hours after (F, I, L) being exposed to UVC at a dose of 6.48 J/cm2, respectively, from the same mouse. Arrow in panel C: UVC-induced lesion on mouse skin. Arrows in panels D-F: mouse skin surface. Arrow in panel 5L shows epidermal shrinkage. Scale bars: 20 µm.