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KOH test on a vaginal wet mount, showing slings of pseudohyphae of Candida albicans surrounded by round vaginal epithelial cells, conferring a diagnosis of candidal vulvovaginitis. The KOH test , also known as a potassium hydroxide preparation or KOH prep , is a quick, inexpensive fungal test to differentiate dermatophytes and Candida albicans ...
Malassezia furfur is a fungus that lives on the superficial layers of the dermis.It generally exists as a commensal organism forming a natural part of the human skin microbiota, but it can gain pathogenic capabilities when morphing from a yeast to a hyphal form during its life cycle, through unknown molecular changes. [2]
Superficial scrapes of skin examined underneath a microscope may reveal the presence of a fungus.This is done by utilizing a diagnostic method called KOH test, [6] wherein the skin scrapings are placed on a slide and immersed on a dropful of potassium hydroxide solution to dissolve the keratin on the skin scrappings thus leaving fungal elements such as hyphae, septate or yeast cells viewable.
Fungal culture medium can be used for positive identification of the species. The fungi tend to grow well at 25 degrees Celsius on Sabouraud agar within a few days to a few weeks. [8] In the culture, characteristic septate hyphae can be seen interspersed among the epithelial cells, and the conidia may form either on the hyphae or on ...
It can be used to diagnose α1-antitrypsin deficiency if periportal liver hepatocytes stain positive. Aggregates of PAS-positive lymphocytes are present in epidermis in Mycosis fungoides and Sézary syndrome, called Pautrier microabscesses. Ewing sarcoma; Erythroleukemia, a leukemia of immature red blood cells. These cells stain a bright fuchsia.
The scrapings are mixed with potassium hydroxide (KOH). [8] The KOH lyses the nonfungal debris. [8] The skin scrapings are cultured on Sabouraud's agar at 25°C and allowed to grow for about a week. H. werneckii can generally be distinguished due to its two-celled yeast form and the presence of septate hyphae with thick, darkly pigmented walls. [5]
As the hair continues to grow outwards, hyphae are brought to the surface (scalp) and arthroconidia are produced. [7] Eventually due to mechanical forces (the movement of the fungi) and keratinase (a chymotrypsin-like enzyme with optimal activity at an acidic pH), all but 1–2 mm of the diseased hair follicle weakens and falls off.
Basement membranes can also show up in a PAS stain and can be important when diagnosing renal disease. Due to the high volume of carbohydrates within the cell wall of hyphae and yeast forms of fungi, the Periodic acid -Schiff stain can help locate these species inside tissue samples of the human body.