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Specimen: Skin scrapings, hair (plucked), nail clippings. As much material as feasible should be provided. The growing edge of the infection is the best area to sample. Skin biopsy: fresh and formalin fixed.

Method: Microscopy: keratinised tissues are treated with potassium hydroxide and stained with eg lactophenol blue or fluorescent dyes to detect hyphae of dermatophytes. Paraffin sections of biopsies are occasionally required. Culture: many pathogenic fungi will grow slowly on conventional media but may be recovered more reliably on special fungal media, which require incubation for up to 4 weeks. Susceptibility tests to antifungal agents are unreliable but can occasionally be of value to detect resistance.

Application: Investigation of suspected yeast infection, tinea, ringworm (dermatophyte infection). Suspected deep fungal skin infections (biopsy required) eg sporotrichosis, mucormycosis, chromomycosis, mycetoma.

Interpretation: Typical microscopic appearance indicates fungal infection but does not identify the particular fungal species. Culture of yeast or fungus provides species identification.

Reference: Merz WD and Roberts GD. In: Murray PR et al eds. Manual of Clinical Microbiology. 6th ed. ASM Press 1995.

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