Microsporum audouinii
| Microsporum audouinii | |
|---|---|
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| Scientific classification | |
| Kingdom: | Fungi |
| Division: | Ascomycota |
| Class: | Eurotiomycetes |
| Order: | Onygenales |
| Family: | Arthrodermataceae |
| Genus: | Microsporum |
| Species: |
Microsporum audouinii Gruby (1843) |
Microsporum audouinii is an anthropophilic fungus in the genus Microsporum. It is a type of dermatophyte that colonizes keratinized tissues (primarily hair) causing infection. The fungus is characterized by its spindle shaped macroconidia (7-30 × 35-160 µm), clavate microconidia (2.5-3.5 × 4-7 µm) as well as its pitted or spiny external walls.
This fungus is often found in soil that is rich in keratinous material. However, there are other factors that can influence its growth, such as pH, relative humidity, organic carbon, nitrogen and temperature.Microsporum audouinii appears to prefer a neutral pH in the range of 6.8-7.0 and room temperature for growth. Drastic increases or decreases in temperature can inhibit its growth.Microsporum audouinii is effective in utilizing its carbon sources, but growth is strongest in the hexoses (glucose, mannose and fructose) and weakest in maltose, sucrose, lactose and galactose. It is unable to synthesize the vitamins thiamine, niacin and riboflavin and requires an exogenous supply of these materials to support its growth. The fungus is only able to utilize organic nitrogen sources, particularly nitrogen from arginine and urea.
Microsporum audouinii causes the infections Tinea capitis (scalp ringworm) and Tinea corporis. These superficial dermal diseases are generally found in prepubescent children (starting at 6 months) and rarely affect adults. There are a few reasons why children are more susceptible to M. audouinii. Differences in the chemical composition and quantity of the triglycerides in hair sebum secreted are the primary reasons. In instances whereby the triglyceride content in the sebum decreases so does the susceptibility of a person to the fungus. Cases like those are seen in postmenopausal women of whom suffer hormonal changes which can contribute to triglyceride reduction. In addition, increased sweat production as well as the presence of Pityrosporum ovale decreases the ability for M. audouinii to thrive.Pityrosporum ovale is an opportunistic lipophilic yeast that is a part of the human cutaneous flora in adults. In most cases of adult onset Tinea capitis due to M. audouinii, there is at least one predisposing factor such as immunocompromise (e.g., diabetes mellitus, systemic lupus, organ transplant and HIV), a local animal reservoir (e.g., infected pet or farm animal) and hormonal changes in postmenopausal women.
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