Author: Hon A/Prof Amanda Oakley, Dermatologist, Hamilton, New Zealand, 2003.
To establish or confirm the diagnosis of a fungal infection, skin, hair and nail tissue is collected for microscopy and culture (mycology).
Specimens for fungal microscopy and culture may be:
They are transported in a sterile container or a black paper envelope.
The material is examined by microscopy by one or more of these methods:
Microscopy can identify a dermatophyte by the presence of:
Fungal elements are sometimes difficult to find, especially if the tissue is very inflamed, so a negative result does not rule out fungal infection.
A yeast infection can be identified by the presence of:
Culture identifies which organism is responsible for the infection:
Growing the fungus in culture may take several weeks, incubated at 25–30ºC. The specimen is inoculated into a medium such as Sabouraud's dextrose agar containing cycloheximide and chloramphenicol. The cycloheximide is left out if a mould requires identification.
A negative culture may arise because:
The culture of yeasts and moulds may be due to harmless colonisation rather than infection. The infection may be secondary to an underlying skin disease such as psoriasis.
Blood tests are not useful for the diagnosis of superficial fungal infections. But in subcutaneous and systemic infection, several tests may be helpful.
New point-of-care tests for some fungal infections are reported to be accurate but are not yet widely available.
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