Trichosporon asahii: etiology, epidemiology, virulence factors and tolerance of biocides of clinical isolates

Abstract

Trichosporon spp. are opportunistic, urease-positive, non-encapsulated yeast-like fungi, widely distributed in the environment, and increasingly isolated in clinical settings. These fungi can cause invasive and disseminated infections with reported mortality rates ranging from 30% to 90%. Given the challenges in diagnosing, and treating Trichosporon infections, advancing research into their phenotypic diversity, epidemiological patterns, virulence factors, and antifungal sensitivity is essential. This study aimed to evaluate the virulence characteristics of Trichosporon asahii isolates obtained from the microbiology service of a laboratory located in Juiz de Fora, Minas Gerais, by analyzing physiological, and clinical aspects related to infection. The investigation included resistance to major antifungal agents, tolerance to biocides, biofilm formation, and efflux pump activity, as well as correlating laboratory findings with clinical data from affected individuals. This descriptive, experimental, and cross-sectional study analyzed 37 clinical isolates of T. asahii collected between 2020 and 2023 from both hospitalized and non-hospitalized individuals, regardless of age or sex. The isolates were identified through morphological, physiological, and biochemical methods. Virulence factors evaluated included coagulase, and catalase production (tested with rabbit plasma, and 3% hydrogen peroxide, respectively), biofilm formation (using the safranin adherence test), hemolytic activity (on sheep blood agar enriched with 2% glucose), and efflux pump activity (using ethidium bromide). Antifungal sensitivity was determined by the disk diffusion method, and tolerance to biocides, including sodium hypochlorite, hydrogen peroxide, benzalkonium chloride, and ethyl alcohol, were assessed. Clinical data, such as infection site, outcomes, and length of hospitalization, were obtained from electronic medical records. A total of 37 clinical isolates of T. asahii were identified, with 83.8% (33/37) originating from hospitalized individuals, 81.8% of which were collected in intensive care units. The average hospital stay was 35 days, and the overall mortality rate was 51.6%. All isolates were sensitive to azole antifungals, but four isolates exhibited resistance to amphotericin B, and all exhibited intrinsic resistance to caspofungin, as expected. Hemolytic activity, and biofilm formation were observed in 75% and 62.5% of isolates, respectively, with higher frequencies among individuals who died; however, similar rates in survivors suggest these factors alone do not determine outcomes. None of the isolates produced coagulase or catalase, indicating these enzymes likely do not play a significant role in T. asahii pathogenicity. Biocide tolerance testing revealed the largest inhibition zones for 2% sodium hypochlorite, suggesting lower tolerance, while efflux pump activity was highly expressed across all clinical isolates. Mortality predominantly affected elderly males with comorbidities such as shock, pneumonia, and sepsis. These findings underscore the clinical importance of T. asahii, especially in critically ill and hospitalized individuals, highlighting its ability to express multiple virulence factors, including biofilm formation, efflux pump activity, and tolerance to biocides that may contribute to its persistence in healthcare environments. The presence of antifungal resistance associated with severe cases reinforces the need for early detection, resistance monitoring, and a deeper understanding of its pathogenic mechanisms. Mapping clinical, epidemiological, and microbiological data is crucial for improving infection control strategies and guiding more effective, and targeted therapeutic interventions.