Morphology and Descriptions of Endemic Fungal Infections with Yeasts in Tissues Broad-based budding yeasts: • Description: Broad-based budding yeasts (10-15 microns in size) • Consistent with Blastomyces dermatitidis, however endospores of Coccidioides spp, Candida spp, Histoplasma, Cryptococcus, and Aspergillus conidia can be confused histologically Narrow-based budding yeasts with mucicarmine positive capsule: • Description: Narrow-based budding yeasts (4-10 microns in size) with thick mucicarmine positive capsule and positive with melanin stains (Fontana Masson) • Consistent with Cryptococcus spp; however Candida spp and Histoplasma can be confused histologically Small yeasts with narrow based budding: • Description: small yeasts (2-4 microns in size) with narrow based budding grouped in clusters inside macrophages • Consistent with Histoplasma capsulatum however small variant of B. dermatitidis, capsule deficient Cryptococcus, endospores of Coccidioides spp, Pneumocystisjirovecii, Penicillium marneffei, Candida glabrata can be confused histologically. Spherules with multiple endospores: • Description: spherules with multiple endospores (10-100 microns in size) • Consistent with Coccidioides spp; however Blastomyces, Histoplasma, Candida, Pneumocystis, and other yeasts can be confused histologically when no spherules are present In addition, Rhinosporidium seeberi has sporangia with endospores which are larger Morphology and Descriptions of Fungal Infections with Hyphae or Pseudohyphae in Tissues Yeasts with Pseudohyphae: • Description: Small yeasts (3-5 microns In size) intermingled with pseudohyphae and hyphae • Consistent with Candida spp. however Aspergillus spp. and other hyaline fungi can be confused histologically Non-pigmented (hyaline), septated hyphae: • Description: acute angle branching • Consistent with Aspergillus spp, Fusarium spp, Scedosporium spp, Trichoderma spp, paecilomyces spp and others. Mucorales genera can sometimes have this morphology Non-pigmented (hyaline), Pauciseptate Hyphae: • Description: pauciseptate ribbon-like hyphae with right angle branching • Consistent with Mucorales genera; however Asperglllus spp. and other septated hyaline hyphae can sometimes have this Pigmented Yeasts and Hyphae with Septations: • Description: pigmented irregular hyphae and yeast-like structures both with septations • Consistent with dematiaceous fungi including: Madurella spp, Fonsecaea spp, Cladophialophora spp, Exophiala spp, Curvularia spp, Bipolaris spp, and others Dr. Sara Dong @swinndong #yeasts #fungal #fungi #infections #microbiology #differential #diagnosis #morphology #pathology #atlas
