Opportunistic fungi in tropical beaches: Diversity, WHO fungal priority pathogens, and antifungal resistance case study.

Tropical coastal regions, despite being major tourist destinations, remain underexplored in terms of their role as potential reservoirs of opportunistic fungal pathogens, particularly those listed on the WHO Fungal Priority Pathogens List (FPPL). This case study presents the first integrative molecular and culture-based assessment of fungal communities in beach sand from three sites along the coastline of Prachuap Khiri Khan, Thailand. Using ITS metabarcoding and culture-based methods, we characterized fungal diversity, detected taxa from genera that include FPPL-listed species, and assessed antifungal susceptibility. The results indicated differences in beta diversity among sites; environmental variables showed directional influence on community variation, with temperature significantly associated with the observed patterns, while moisture was not statistically significant. The urban adjacent SON site exhibited a higher prevalence of FUNGuild predicted opportunistic pathogens, while the more remote DSN site showed fewer. Five of the thirteen isolated fungi exhibited elevated minimum inhibitory concentrations (MICs) against azoles and flucytosine, isolates affiliated with Aspergillus section Terrei, which also showed genetic similarity to clinical strains. These findings suggest that recreational beaches may act as potential environmental reservoirs of opportunistic and antifungal-resistant fungi. However, only Fusarium neocosmosporiellum TPS1-10, a high-priority FPPL pathogen, was successfully isolated among taxa detected by ITS metabarcoding, and it did not exhibit elevated MIC values. Overall, these results highlight the need for routine fungal monitoring in recreational beach environments, in accordance with WHO guidelines, particularly in the context of increasing antifungal use, climate change, and growing beach tourism.