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Immunology and Infection

Rose Bengal-Mediated Photodynamic Therapy to Inhibit Candida albicans

Published: March 24th, 2022



* These authors contributed equally

The growing incidence of drug-resistant Candida albicans is a serious health issue worldwide. Antimicrobial photodynamic therapy (aPDT) may offer a strategy to fight against drug-resistant fungal infections. The present protocol describes Rose bengal-mediated aPDT efficacy on a multidrug-resistant C. albicans strain in vitro.

Invasive Candida albicans infection is a significant opportunistic fungal infection in humans because it is one of the most common colonizers of the gut, mouth, vagina, and skin. Despite the availability of antifungal medication, the mortality rate of invasive candidiasis remains ~50%. Unfortunately, the incidence of drug-resistant C. albicans is increasing globally. Antimicrobial photodynamic therapy (aPDT) may offer an alternative or adjuvant treatment to inhibit C. albicans biofilm formation and overcome drug resistance. Rose bengal (RB)-mediated aPDT has shown effective cell killing of bacteria and C. albicans. In this study, the efficacy of RB-aPDT on multidrug-resistant C. albicans is described. A homemade green light-emitting diode (LED) light source is designed to align with the center of a well of a 96-well plate. The yeasts were incubated in the wells with different concentrations of RB and illuminated with varying fluences of green light. The killing effects were analyzed by the plate dilution method. With an optimal combination of light and RB, 3-log growth inhibition was achieved. It was concluded that RB-aPDT might potentially inhibit drug-resistant C. albicans.

1. aPDT system preparation

  1. Cut four green light-emitting diodes (LEDs) from a LED strip (see Table of Materials) and align them with four wells of a 96-well plate (Figure 1).
    NOTE: The LEDs were arranged into a 4 x 3 array. The back of the LED was adhered to a heat sink to disperse heat during irradiation.
  2. Measure the fluence rate11 of the LED at 540 nm with a light power meter (see Table of Materi.......

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Figure 1 shows the aPDT system being used in the present study. Since high temperatures may cause significant cell death, the LED array is cooled by an electric fan, and a heat sink is used during irradiation to maintain a constant temperature at 25 ± 1 °C. The heat effect can be discounted. Having an even light distribution is also an important determining factor for a successful aPDT; therefore, it is critical to align the LED light bulb to the well precisely during illumination........

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Encouraging results of clinical applications of RB-PDT for fungal keratitis have been reported recently19. The absorption peak of RB is at 450-650 nm. It is essential to determine the fluence rate of the light source for a successful aPDT. A high fluence (usually >100 J/cm2) is required to treat cancer cells, while a lower fluence is expected to treat infected lesions6. A high fluence means a long exposure time which may not be practical in a clinical setting.......

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