First morphological description of Histoplasma capsulatum Indonesian strain: Successful yeast phase conversion

Background: Indonesia is endemic for histoplasmosis, yet there is limited research on the Indonesian strain of H. capsulatum. This study aims to convert H. capsulatum to its yeast phase and provides detailed morphological descriptions and information about this phase. Method: Two Indonesian strains of H. capsulatum were analyzed using various media. The solid media employed were MLGema, potato starch-egg medium, and modified brain heart infusion (BHI) semisolid medium. For liquid media, modified Müeller Hinton broth (MHB) and modified BHI broth (BHIB) were utilized. The mold phase of H. capsulatum was inoculated and incubated at 37°C, with the colony and microscopic appearances observed. Fungal microscopic morphology was examined using lactophenol cotton blue (LPCB) and 3% Giemsa staining. Results: The complete conversion of H. capsulatum to the yeast phase was achieved in solid MLGema medium and potato starch-egg medium for both strains after one month in both media. MLGema outperformed potato starch-egg medium in both number and size of colonies. H. capsulatum appeared as oval-shaped yeast cells measuring 2-7 μm with budding. Our strain was identified as H. capsulatum, not Histoplasma duboisii. Cysteine, egg, and glucose were found to be crucial nutrients for successful conversion. Conclusion: Our study successfully converted the Indonesian strain of Histoplasma using MLGema and potato starch-egg media. This is the first to provide a morphological description of the yeast phase of the Indonesian strain, confirming it as H. capsulatum. For the analyzed strain, thorough genetic analysis of the strains is necessary to confirm the unique pattern.