Candida albicans is an opportunistic fungal pathogen of clinical importance and is the primary cause of fungal‐associated wound infections, sepsis, or pneumonia in immunocompromised individuals. With the rise in antimicrobial resistance, it is becoming increasingly difficult to successfully treat fungal infections using traditional antifungals, signifying that alternative non‐traditional approaches must be explored for their efficacy.

We investigated the combination of antimicrobial blue light (aBL) and quinine hydrochloride (Q‐HCL) for improved inactivation of C. albicans, in vitro and in vivo, relative to either monotherapy. In addition, we evaluated the safety of this combination therapy in vivo using the TUNEL assay.

The combination of aBL (108 J/cm²) with Q‐HCL (1 mg/mL) resulted in a significant improvement in the inactivation of C. albicans planktonic cells in vitro, where a 7.04 log₁₀ colony forming units (CFU) reduction was achieved, compared with aBL alone that only inactivated 3.06 log₁₀ CFU (P < 0.001) or Q‐HCL alone which did not result in a loss of viability. aBL + Q‐HCL was also effective at inactivating 48‐hour biofilms, with an inactivation 1.73 log₁₀ CFU at the dose of 108 J/cm² aBL and 1 mg/mL Q‐HCL, compared with only a 0.73 or 0.66 log₁₀ CFU by aBL and Q‐HCL alone, respectively (P < 0.001). Transmission electron microscopy revealed that aBL + Q‐HCL induced morphological and ultrastructural changes consistent with cell wall and cytoplasmic damage. In addition, aBL + Q‐HCL was effective at eliminating C. albicans within mouse abrasion wounds, with a 2.47 log₁₀ relative luminescence unit (RLU) reduction at the dose of 324 J/cm² aBL and 0.4 mg/cm² Q‐HCL, compared with a 1.44 log₁₀ RLU reduction by aBL alone. Q‐HCL or nystatin alone did not significantly reduce the RLU. The TUNEL assay revealed some apoptotic cells before and 24 hours following treatment with aBL + Q‐HCL.

The combination of aBL + Q‐HCL was effective at eliminating C. albicans both in vitro and in vivo. A comprehensive assessment of toxicity (cytotoxicity and genotoxicity) is required to fully determine the safety of aBL + Q‐HCL therapy at different doses. In conclusion, the combination of aBL and Q‐HCL may be a viable option for the treatment of cutaneous candidiasis. Lasers Surg. Med. © 2019 Wiley Periodicals, Inc.