Antifungal-resistant yeasts detected in recreational coastal waters of Rio de Janeiro, Brazil

BACKGROUND: Recreational coastal waters are widely used for leisure activities and require systematic microbiological monitoring to ensure the safety of bathers. However, such surveillance has traditionally focused on fecal indicator bacteria, whereas fungal communities remain largely neglected by regulatory and governmental agencies. AIMS: This study aimed to identify 18 yeasts isolated from three tourist beaches in Rio de Janeiro, Brazil, and to evaluate their antifungal susceptibility, biofilm-forming capacity and growth in saline conditions. METHODS: The molecular identification of the isolates was performed by sequencing the ITS1-5.8S-ITS2 rDNA region. Antifungal susceptibility was determined using the broth microdilution method. Biofilm formation was assessed in 96-well microtiter plates using crystal violet, safranin and XTT. Growth under different salt concentrations was also evaluated. RESULTS: Fungal isolates were identified as Candida parapsilosis species complex (n=5), Candida tropicalis (n=4), Nakaseomyces glabratus (formerly Candida glabrata; n=2), Candidozyma haemuli species complex (formerly Candida haemulonii species complex; n=2), Wickerhamiella infanticola (n=2), and one isolate each of Candida palmioleophila, Candida ecuadorensis and Pichia manshurica. Resistance to azoles was observed in C. tropicalis, N. glabratus, C. haemuli and C. palmioleophila, with variable susceptibility to other antifungals. C. parapsilosis and C. ecuadorensis isolates were susceptible to all tested antifungals. W. infanticola isolates exhibited low MIC values against the antifungals tested, while P. manshurica exhibited elevated MICs to fluconazole and flucytosine. All yeasts formed biofilms on plastic and tolerated NaCl concentrations of up to 7.5%. CONCLUSIONS: These findings demonstrate the presence of clinically relevant opportunistic yeasts in recreational seawater. The isolates exhibited antifungal resistance, salt tolerance, and the ability to form biofilms, all of which pose a potential public health concern.