Mould Identification: A Virtual Self Assessment
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Unknown 34 = Coccidioides immitis/posadasii
|A 34-year-old female presented with an ulcerating lesion on the face. She had a six month travel history which included visits to the USA, Mexico and Argentina. Skin scrapings showed the presence of fungal elements and the culture grew the fungus shown below.|
|Direct Microscopy (KOH stain)|
Direct microscopy of skin scrapings from a cutaneous lesion mounted in 10% KOH and Parker ink solution showing characteristic endosporulating spherules (sporangia) of Coccidioides immitis. The presence of spherules with endospores is diagnostic.
Colonies of C. immitis/posadasii on Sabouraud’s dextrose agar at 25C are initially moist and glabrous, but rapidly become suede-like to downy, greyish white with a tan to brown reverse, however considerable variation in growth rate and culture morphology has been noted.
Microscopy shows typical single-celled, hyaline, rectangular to barrel-shaped, alternate arthroconidia, 2.5-4 x 3-6 µm in size, separated from each other by a disjunctor cell. This arthroconidial state has been classified in the genus Malbranchea and is similar to that produced by many non-pathogenic soil fungi, e.g. Gymnoascus species. WARNING: RG-3 organism. Cultures of Coccidioides immitis/posadasiirepresent a severe biohazard to laboratory personnel and must be handled with extreme caution in an appropriate pathogen handling cabinet. C. immitis/posadasiiis a dimorphic fungus, existing in living tissue as spherules and endospores, and in soil or culture in a mycelial form. Culture identification by exoantigen test is now the method of choice. Exoantigen test: showing a positive result for C. immitis/posadasii.
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