Indoor Yeast Ecology: Updating Knowledge and Evidence for a Previously Unrecognized Dispersal Strategy

Yeasts and yeast-like fungi represent an understudied component of indoor mycobiota, despite including numerous opportunistic human pathogens. This study investigated the diversity, habitats, and potential dispersal mechanisms of yeasts in non-clinical indoor environments. A review of previous studies was combined with new field and laboratory observations. Overall, 1977 yeast occurrence records, including 106 records generated during this study, were analyzed. In total, 83 genera comprising 170 species were identified from 1320 habitat records. Most frequently reported species were Candida parapsilosis (13.8%), Rhodotorula mucilaginosa (7.7%), and Exophiala dermatitidis (7.1%). Habitat records were dominated by wet-cell environments (90.9%), particularly dishwashers, sinks, plumbing systems, tap water and washing machines. Additional habitats included indoor plants, potting soils and wooden materials, the latter representing a previously unreported indoor habitat. Multiple correspondence analysis identified moisture availability as the principal factor structuring habitat associations. Among 89 isolates, ballistospore production, long filamentous thread formation, and dry aerial structures were observed in 3.3%, 2.2%, and 16.9%, respectively. In E. dermatitidis, long filamentous threads were observed to facilitate dispersal by both air currents and contact with surfaces, as confirmed experimentally in one of the investigated strains. These findings expand knowledge of indoor yeast ecology and suggest broader dispersal strategies than previously recognized, while highlighting the need for further ecological and epidemiological studies.