Blastomyces spp. produce large (size), broad-based budding yeast in tissue. The yeast cell walls are thick and double-contoured.
When incubated at 25–30°C, Blastomyces species are slow growing and produce a white, cottony mycelium that darkens to tan with age. Microscopically, the mold demonstrates septate, hyaline hyphae with short unbranched conidiophores, producing single pyriform to round, smooth conidia that measure 2-10 µm. Definitive identification of Blastomyces spp. requires either conversion to its yeast form at 37ºC, or exoantigen or molecular confirmatory tests.
Blastomyces species are found in the Mississippi and Ohio River valleys. They are also endemic to the southeastern US and in areas bordering the Great Lakes. It is thought to thrive in the soil of wooded areas.
54. CDC/Ajello. Image #19914. This Petri dish culture plate contained an unknown growth medium, upon which a colony of Blastomyces dermatitidis had been cultured. PHIL public domain. Created 1966. Accessed January 15, 2023. https://phil.cdc.gov/Details.aspx?pid=19914 55. CDC/Haley. Image #3768. This photomicrograph of a lactophenol cotton blue (LPCB) stained specimen, revealed some of the ultrastructural morphology exhibited by the fungal organism, Blastomyces dermatitidis. PHIL public domain. Created 1969. Accessed January 15, 2023. https://phil.cdc.gov/Details.aspx?pid=3768
