Case of Mixed Infection of Toenail Caused by Candida parapsilosis and Exophiala dermatitidis and In Vitro Effectiveness of Propolis Extract on Mixed Biofilm

Onychomycosis is a chronic fungal nail infection caused by several filamentous and yeast-like fungi, such as the genus Candida spp., of great clinical importance. Black yeasts, such as Exophiala dermatitidis, a closely related Candida spp. species, also act as opportunistic pathogens. Fungi infectious diseases are affected by organisms organized in biofilm in onychomycosis, making treatment even more difficult. This study aimed to evaluate the in vitro susceptibility profile to propolis extract and the ability to form a simple and mixed biofilm of two yeasts isolated from the same onychomycosis infection. The yeasts isolated from a patient with onychomycosis were identified as Candida parapsilosis sensu stricto and Exophiala dermatitidis. Both yeasts were able to form simple and mixed (in combination) biofilms. Notably, C. parapsilosis prevailed when presented in combination. The susceptibility profile of propolis extract showed action against E. dermatitidis and C. parapsilosis in planktonic form, but when the yeasts were in mixed biofilm, we only observed action against E. dermatitidis, until total eradication.