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BLASTOMYCES Mold Species |
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Taxonomic Classifications
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Description and Habitats The sexual state (teleomorph) of Blastomyces
dermatitidis belongs to the family Onygenaceae and is referred to as
Ajellomyces dermatitidis. Ascospores are the sexual spores produced by
this genus. Species Based on
the mycological information provided in the website,
www.doctorfungus.com, Blastomyces
dermatitidis is the only species included in the genus
Blastomyces. Mycosis: BLASTOMYCOSIS Blastomycosis is a chronic granulomatous disease which means that it progresses slowly. Although the pulmonary and skin involvement is the most common, B. dermatitidis frequently affects bone, prostate and other organs. More frequently blastomycosis presents as a cutaneous or a respiratory disease. The cutaneous lesions may be primary (usually self-limiting) or secondary (a manifestation of systemic disease). The patient who presents with a complaint of respiratory symptoms will frequently remark about loss of appetite, loss of weight, fever, productive cough, and night sweats. While these symptoms resemble those of TB, it is not this disease. The X-ray shows obvious pulmonary disease. To make the specific diagnosis, the physician must be aware of blastomycosis. Sputum sent to the lab for "culture" will not grow the organism. The lab must be alerted to look for fungal organisms or to look specifically for blastomyces. Some patients have a sub-clinical or "flu-like" response to infection. B. dermatitidis can frequently be demonstrated in a KOH preparation of pus from a skin lesion. A typical cutaneous lesion shows central healing with microabscesses at the periphery. A pus specimen may be obtained by nicking the top of a microabscess with a scalpel, obtaining the purulent material and making the diagnosis in 5 min. by microscopic examination with KOH. This organism has a characteristic appearance of a double contoured wall with a single bud on a wide base. There are no specific virulence factors for B. dermatitidis. Laboratory specimens depend on the manifestation of the disease: If there are skin lesions, send skin scrapings or pus. If there is pulmonary involvement, send sputum. Other specimens include biopsy material and urine. Occasionally, the organism can be isolated from urine as it often infects the prostate.
Macroscopic
Features Being
a thermally dimorphic fungus, Blastomyces dermatitidis behaves
diversely at different temperatures. The morphology of the fungus is
mold-like at 25°C and yeast-like at 37°C. Although the demonstration of
conversion from the mycelial form to yeast form is favorable for definitive
identification of Blastomyces dermatitidis, it remains possible only
for few isolates pathogenic to humans. Other ways of verification of the
identification are by use of exoantigen test, direct flourescent antibody
and nucleic acid probes. Below are the macroscopic features of the fungus: Microscopic
Features
Similar to the colony morphology, microscopic appearance of the fungus also
depends on the temperature of isolation: Laboratory Precautions Blastomyces dermatitidis is potentially dangerous and requires biological safety cabinet for all manipulations. Susceptibility In vitro susceptibility testing procedures have not been yet standardized
for Blastomyces dermatitidis as well as other thermally dimorphic
fungi, except for mycelial phase of
Sporothrix schenckii. However, there are reports on in vitro
activity of some antifungal agents against Blastomyces. In general,
amphotericin B,
ketoconazole and
itraconazole are highly active. In contrast, fluconazole MICs against
Blastomyces are unacceptably high. The novel agents,
voriconazole,
posaconazole, VER-002, and
caspofungin appear active against Blastomyces. |
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Browse these Webpages:
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The mycological information gathered and organized in
this extensive research on the |
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