Antimicrobial Photodynamic Inactivation Inhibits Candida albicans Virulence Factors and Reduces In Vivo Pathogenicity

Abstract

The objective of this study was to evaluate whether Candida albicans exhibits altered pathogenicity characteristics following sublethal antimicrobial photodynamic inactivation (APDI) and if such alterations are maintained in the daughter cells. C. albicans was exposed to sublethal APDI by using methylene blue (MB) as a photosensitizer (0.05 mM) combined with a GaAlAs diode laser ( 660 nm, 75 mW/cm 2 , 9 to 27 J/cm 2 ). In vitro, we evaluated APDI effects on C. albicans growth, germ tube formation, sensitivity to oxidative and osmotic stress, cell wall integrity, and fluconazole susceptibility. In vivo, we evaluated C. albicans pathogenicity with a mouse model of systemic infection. Animal survival was evaluated daily. Sublethal MB-mediated APDI reduced the growth rate and the ability of C. albicans to form germ tubes compared to untreated cells (P < 0.05). Survival of mice systemically infected with C. albicans pretreated with APDI was significantly increased compared to mice infected with untreated yeast (P < 0.05). APDI increased C. albicans sensitivity to sodium dodecyl sulfate, caffeine, and hydrogen peroxide. The MIC for fluconazole for C. albicans was also reduced following sublethal MB-mediated APDI. However, none of those pathogenic parameters was altered in daughter cells of C. albicans submitted to APDI. These data suggest that APDI may inhibit virulence factors and reduce in vivo pathogenicity of C. albicans. The absence of alterations in daughter cells indicates that APDI effects are transitory. The MIC reduction for fluconazole following APDI suggests that this antifungal could be combined with APDI to treat C. albicans infections. Management of infections caused by clinically relevant fungal pathogens is a challenge due to the incidence of resistance that can develop during therapy, especially in immunocompromised individuals (1). The increasing need for prolonged use of antifungal drugs, longer than usually recommended for antibiotics, is accompanied by a corresponding increased incidence of side effects. Furthermore, the limited number of available antifungal compounds and the need to determine the susceptibility profile of the organism also complicate the treatment of these infections (2).The fungal species Candida albicans is part of the commensal flora of the human gastrointestinal and genitourinary tracts and can cause superficial infections of the mucosa and skin (3, 4). The infection depends on imbalances between increased C. albicans virulence attributes and impaired host defense systems. In immunocompromised individuals, however, C. albicans may invade deeper tissues, penetrate the blood vessels, and cause life-threatening systemic infections (3, 5).Photodynamic therapy (PDT) is a light-based treatment platform that is under development for several applications in oncology, dermatology, and ophthalmology, and it has recently been investigated as an antimicrobial therapy. The combination of nontoxic dyes referred to as photosensitizers (PS) and harmless low-intensity visible light generate...

Photoinactivation of Candida albicans using methylene blue as photosensitizer

“…The three main components of PDT are visible light, FS and oxygen 16 . Due to the fact that they absorb light with high efficiency, in some region of the visible spectrum, some of the FSs are able to induce or participate in photochemical reactions and produce reactive oxygen molecules 5,14,[17][18] .…”

“…The light therapeutic properties studies with antimicrobial purpose are primarily motivated by resistance cases of conventional antimicrobial 3,6,[11][12][13][14] . The need to overcome these deficiencies led to the exploration of Petri dishes containing Agar Sabouraud Dextrose culture medium.…”

“…Currently, the light-based antimicrobial treatment is called Photodynamic therapy [4][5]15 . The three main components of PDT are visible light, FS and oxygen 16 .…”

“…The log 10 (CFU/mL) results for each tested condition was compared using Kruskal-Wallis statistical test and in the case of a significant difference, multiple Photoinactivation of Candida albicans alternative treatments and unconventional approaches to the control of microbial infections 14 .…”

“…Photodynamic Therapy (PDT) is a treatment already used in several medical specialties, such as dermatology, oncology and ophthalmology, and has been investigated as an antimicrobial therapy, which consists in the administration of a photosensitizing (FS) dye, followed by the lesion illumination with visible light, forming cytotoxic species in the presence of oxygen, such as the singlet oxygen and free radicals 4 . These reactive chemical species are mostly toxic and can cause: destruction of proteins, lipids, nucleic acids, and other cell components, resulting in the destruction of microbial cells 5 .…”