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Types of Fungi: There are five phyla of fungi: Chytridiomycota, Zygomycota, Glomeromycota, Ascomycota, and Basidiomycota. The following is a brief description of each phylum: 1. Chytridiomycota: Chytrids, the organisms found in Chytridiomycota, are usually aquatic and microscopic. They are usually aRead more
Types of Fungi: There are five phyla of fungi: Chytridiomycota, Zygomycota, Glomeromycota, Ascomycota, and Basidiomycota.
The following is a brief description of each phylum:
1. Chytridiomycota: Chytrids, the organisms found in Chytridiomycota, are usually aquatic and microscopic. They are usually asexual, and produce spores that move around using flagella, small tail-like appendages. The chytrid Batrachochytrium dendrobatidis can cause a fungal infection in frogs by burrowing under their skin, and it has recently devastated populations of harlequin frogs, killing off two-thirds of them in Central and South America.
2. Zygomycota: Zygomycetes are mainly terrestrial and feed off of plant detritus or decaying animal material. They also cause problems by growing on human food sources. One example of a zygomycte is Rhizopus stolonifer, a bread mold. The hyphae of zygomycetes are not separated by septa, making their mycelia essentially one large cell with many nuclei. They usually reproduce asexually, through spores.
3. Glomeromycota: Glomeromycetes make up half of all fungi found in soil, and they often form mycorrhizae with plants; in fact, 80-90 percent of all land plants develop mycorrhizae with glomeromycetes. The fungi obtain sugars from the plant, and in return, dissolve minerals in the soil to provide the plant with nutrients. These fungi also reproduce asexually.
4. Ascomycota: Ascomycetes are often pathogens of plants and animals, including humans, in which they are responsible for infections like athlete’s foot, ringworm, and ergotism, which causes vomiting, convulsions, hallucinations, and sometimes even death. However, some ascomycetes normally are found inside humans, such as Candida albicans, a yeast which lives in the respiratory, gastrointestinal, and female reproductive tracts. Ascomycetes have reproductive sacs known as asci, which produce sexual spores, but they also reproduce asexually.
5. Basidiomycota: Like ascomycetes, basidiomycetes also produce sexual spores called basidiospores in cells called basidia. Basidia are usually club-shaped, and basidiomycetes are also known as club fungi. Most basidiocytes reproduce sexually. Mushrooms are a common example of basidiomycetes.
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Diagnostic Methods for Dermatophyte Infections: 1. Potassium hydroxide (KOH) microscopy: Values: aids in visualizing hyphae and confirming the diagnosis of dermatophyte infection Procedure: obtain scale from the active border of a lesion, pull out several loose hairs from the affected area or, in thRead more
Diagnostic Methods for Dermatophyte Infections:
1. Potassium hydroxide (KOH) microscopy:
Values: aids in visualizing hyphae and confirming the diagnosis of dermatophyte infection Procedure: obtain scale from the active border of a lesion, pull out several loose hairs from the affected area or, in the case of nails, obtain subungual debris. A moist cotton swab rubbed vigorously over the active border of a lesion works as well as a scalpel blade and is safer. Transfer the scale, hair, or debris to a glass slide, and add a few drops of 10% to 20% KOH. For nail material or hair, gently warm the slide. The wet-mount preparation is then examined under a microscope (×400) with back-and-forth rotation of the focus knobs. This technique aids the visualization of hyphae (branching, rod-shaped filaments of uniform width with lines of separation [septa]). In tinea capitis, the hair shaft may be uniformly coated with minute dermatophyte spores.
2. Wood’s lamp examination (ultraviolet light):
Value: generally of limited usefulness, because most dermatophytes currently seen in the United States do not fluoresce; may have value in the following situations: For diagnosing a brown, scaly rash in the scrotum or axilla: erythrasma, caused by the bacterium corynebacterium minutissimum, fluoresces a brilliant coral red, whereas tinea cruris or cutaneous candidal infections do not fluoresce.
For diagnosing tinea (pityriasis) Versicolor, which fluoresces pale yellow to white
For diagnosing tinea capitis caused by two zoophilic Microsporum species that fluoresce blue-green.
3. Fungal culture:
Value: slow and expensive, but useful to confirm the diagnosis of onychomycosis when long-term oral therapy is being considered
Procedure*: Skin, nail, or hair scrapings are sent in a sterile container for inoculation on Sabouraud’s dextrose agar by a hospital or reference laboratory. The culture usually takes 7 to 14 days to be declared positive; it must be held for 21 days to be declared negative.
4. Skin or nail biopsy:
See lessValue: may guide treatment decisions when the diagnosis is difficult to establish, a dermatophyte infection has not responded to previous treatment, or KOH microscopy is negative in a patient with dystrophic nails.