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Skin infections

Fungal infections key points test

To make sure you have understood the key points of this section, select the correct option:

Dermatophye infections include: * Candida tropicalis * Trichosporon beigelii * Malassezia globosa *! Epidermophyton floccosum Explanation: Dermatophytes are trichophyton, microsporum and epidermophyton species. Malassezia and candida species are yeasts. Trichosporon beigelii is the fungus causing favus, which has not been seen in New Zealand. Tinea pedis is most frequently due to: *! Trichophyton rubrum * Malassezia furfur * Scopulariopsis brevis * Candida albicans Explanation: More than half of all fungal foot infections are caused by _T. rubrum_. Scopulariopsis (a mould) rarely causes tinea pedis. Candida is one of the causes of athlete's foot, but by definition is not tinea (a term used for dermatophyte infection). Malassezia is almost never cultured from feet. Select the least likely fungus to cause nail infection: * Trichophyton rubrum *! Malassezia furfur * Scopulariopsis brevis * Candida albicans Explanation: Malassezia species rarely cause nail infections. _T rubrum_ and _T interdigitale_ are the most common causes with candida and scopulariopsis cultured less frequently. Select which organism found in the scalp fluoresces on Wood's light examination: * Trichophyton tonsurans *! Microsporum canis * Malassezia furfur * Trichophyton violaceum Explanation: Although _T tonsurans_ and _T violaceum_ may cause tinea capitis, they do not fluoresce on exposure to long wavelenth ultraviolet radiation (UVA). Malassezia species associated with pityriasis capitis (dandruff) and seborrhoeic dermatitis do not fluoresce. However, pityriasis versicolor due to related organisms may fluoresce a green-yellow colour. Tinea unguium is best confirmed prior to treatment by: * Blue-top swab for microscopy and culture * Smear for wet ground examination *! Clippings for KOH microscopy and culture * Wood’s light examination Explanation: Fungal nail infections are identified by positive microscopy on nail clippings and scrapings treated with potassium hydroxide (OH). The responsible organisms cannot be identified by fluorescence or standard bacterial culture; fungal culture requires a different medium, lower temperature and prolonged observation time Select the least likely to have provoked candidiasis: * Diabetes mellitus *! Flucloxacillin * Amoxycillin/clavulanic acid * Pregnancy Explanation: A number of physiological and disease states promote candida infections including broad spectrum antibiotics, diabetes and pregnancy. The more narrow spectrum flucloxacillin is less likely than the other options to provoke candidiasis. Malassezia infection is most often reported to have: * Positive microscopy and positive culture * Negative microscopy and positive culture * Negative microscopy and negative culture *! Positive microscopy and negative culture Explanation: Although malassezia yeast buds ('meatballs') and hyphae ('spaghetti') are readily seen on KOH microscopy, the organism is difficult to culture in standard fungal media.