Successive applications of Antimicrobial Photodynamic Therapy effects the susceptibility of Candida albicans grown in medium with or without fluconazole

Abstract

Antimicrobial Photodynamic Therapy (aPDT) was introduced as a therapy due to resistance that microorganisms have developed to conventional drugs. The study aimed to evaluate the potential of successive applications of aPDT in effecting Candida albicans susceptibility and also whether the presence of fluconazole effected the recovery of the fungi in the culture medium. Planktonic cultures and biofilm were subjected to successive applications of Photodithazine-mediated (25 mg/L) LED-associated aPDT (660 nm, 34 mW/cm2). Plating was performed on Sabouraud Dextrose Agar supplemented or not with fluconazole to recover colony-forming units per milliliter (CFU/mL). Surviving cells were recovered, recultivated, and again exposed to the treatment. The treatments were performed until not enough colonies were available for recultivation and continuation of the protocol. The complete inactivation of the fungus was obtained after three and five applications for planktonic culture and biofilm, respectively. A reduction of 6.3 log10 was observed after third applications in the planktonic cultures grown on medium without fluconazole, while there was a 7 log10 reduction of these cultures grown on fluconazole medium. However, a reduction of 6.1 log10 occurred for biofilms after fifth applications for cultures grown on medium without fluconazole, while a reduction of 6.7 log10 was observed for cultures grown on medium with the antifungal. Thus, aPDT was potentiated by fluconazole. C. albicans in planktonic and biofilm cultures are susceptible to successive applications of PDZ-mediated aPDT, and tolerance to aPDT is higher in the biofilm.