Blastomyces dermatitidis
A Microbial Biorealm page on the genus Blastomyces dermatitidis
Classification
Fungi; Ascomycota; Ascomycetes; Incertae sedis; Incertae sedis; Incertae sedis; Blastomyces
Description and significance
Blastomyces dermatitidis is a dimorphic fungal pathogen, found in the Mid-West and Northern United States and Canada. Inhaling Blastomyces dermatitidis spores can cause blastomycosis, which commonly affects the lungs and skin. It also affects the bone, prostate and other organs (2). Although the disease was long thought to be restricted to the North American continent, in recent years autochthonous cases have been diagnosed in Africa, Asia and Europe. All available clinical and epidemiological evidence indicates that humans and lower animals contract blastomycosis from some source in nature. However, the natural habitat of B. dermatitidis has yet to be clearly delineated, despite some reports of its isolation from soil (1).
Genome structure
This is not clear yet
Cell structure, metabolism & life cycle
Blastomyces dermatitidis grown on Sabouraud's dextrose agar at 25C, produces colonies that are variable in both morphology and rate of growth. They may grow rapidly, producing a fluffy white mycelium, or slowly as smooth, tan colored, non-sporulating colonies. Growth and sporulation are enhanced by nitrogenous substances found in starling dung and yeast extract. Strains usually become pleomorphic with age and take on multiple structural forms. Grown on blood agar at 37C, the colonies are wrinkled and folded, smooth and yeast-like. Microscopically, the organism produces the characteristic yeast phase as seen in tissue pathology. B. dermatitidis can be described as a dimorphic fungus because it has both a mould and yeast phase (1). It develops a typical yeast form of a thick wall and a single bud with a wide base. This wide base is characteristic of B. dermatitidis, and it is important to be able to recognize this. The cells are 12-15 microns in diameter. The yeast will convert to the mycelial form when incubated at 25 degrees C, taking from 3 to 4 days up to a few weeks. Similarly, the mycelial growth can be converted to yeast form when incubated at 37 degrees C. In the past, the only way to identify the dimorphic fungi was to convert from one form to the other, but now it is possible to take the mycelial growth (which is the easiest to grow), and confirm the isolate with a DNA probe in a matter of hours (2).
Ecology (including pathogenesis)
Describe its habitat, symbiosis, and contributions to environment. If it is a pathogen, how does this organism cause disease? Human, animal, plant hosts? Describe virulence factors and patient symptoms.
Interesting feature
Describe in detail one particularly interesting aspect of your organism or it's affect on humans or the environment.
