LEARNING OBJECTIVE: Recall how potassium hydroxide (KOH) preparation is used in the detection offungi.
Fungi (sing. fungus) are chlorophyll-free, heterotrophic (not self-sustaining) of the same family ofplants (i.e., Thyllophyta) as algae and lichens. They reproduce by spores that germinate into long filaments called hyphae. As the hyphae continue to grow and branch, they develop into a mat of growth called the mycelium (pl. mycelia). From the mycelium, spores are produced in characteristic patterns. These spores, when dispersed to new substances, germinate and form new growths. Reproduction is often asexual, usually by budding (as in yeast), but certain fungi have sexual reproduction.
Common superficial infections of the skin caused by fungi are athlete’s foot and ringworm of the scalp.
A simple and frequently used method of detecting fungi is the potassium hydroxide (KOH) preparation. Fungi are seen in clustered round buds with thick walls, accompanied by fragments of mycelia. Scrapings from the affected area of the skin are mounted in 10% KOH for positive laboratory diagnosis.
To detect fungi in infected tissue using the KOH preparation, follow the steps below.
- Fungi on the skin and nails appear as refractile fragments of hyphae.
- Fungi in the hair appear as dense clouds around the hair stub or as linear rows inside the hair shaft.