Dermatophytes

Dermatophytes: 

Dermatophytes -Varun C N

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Dermatophytes are a group of fungi that predominantly infect the keratin layers, belonging to 3 important genus Microsporum Trichophyton Epidermophyton They possess two important properties Keratinophilic- Ability to digest keratin in vitro in their saprophytic state Keratinolytic- Utilize keratin as a substrate for growth.

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The most common system to classify dermatophytes: • Zoophilic dermatophytes are mainly found in animals but can be transmitted to humans. • Anthropophilic dermatophytes are mainly found in humans and are very seldom transmitted to animals. • Geophilic dermatophytes are found mainly in soil, where they are associated with decomposing hair, feathers, hooves and other keratin sources. They infect both humans and animals.

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The genus produces both micro- and Macroconidia. Macroconidia are multi-septate, with a thin or thick echinulate cell wall, spindle shaped and may be numerous or scarce. The thickness of the cell wall and shape varies depending on the species. Microconidia are pyriform, about 2-3 μ m . Microsporum

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Microsporum audouinii On Sabouraud's dextrose agar, colonies are flat, spreading, greyish-white to light tan-white in colour, and have a dense suede-like to downy surface, suggestive of mouse fur in texture. Reverse can be yellow-brown to reddish-brown in colour. Some strains may show no reverse pigment Macroconidia and microconidia are only rarely produced, most cultures are sterile or produce only occasional thick-walled terminal or intercalary chlamydoconidia 6 Varun C N

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Growth on Rice Grains: Very poor or absent, usually being visible only as a brown discoloration. This is one of the features which distinguish M. audouinii from M. canis 7 Varun C N

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Microsporum canis Flat, spreading, white to cream-coloured, with a dense cottony surface which may show some radial grooves. Colonies usually have a bright golden yellow to brownish yellow reverse pigment, but non-pigmented strains may also occur Macroconidia are typically spindle-shaped with 5-15 cells, verrucose, thick-walled and often have a terminal knob 8 Varun C N

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Growth on Rice Grains: good growth of white aerial mycelium with production of yellow pigment. Microscopy reveals numerous macroconidia 9 Varun C N

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Dysgonic strain of M. canis Dysgonic strains of M. canis are rare but may also occur. Cultures are typically heaped and folded and yellow-brown in colour. Macroconidia are usually absent in these strains. However, typical colonies and macroconidia of M. canis are usually produced by this variant when subcultured onto polished rice grains. 10 Varun C N

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Microsporum canis var. distortum 11 Varun C N

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Microsporum cookei Flat, buff-coloured, suede-like to powdery colony with a deep red-brown reverse. Numerous large, very thick-walled, echinulate (rough) elliptical macroconidia 12 Varun C N

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Microsporum gypseum Colonies are usually flat, spreading, suede-like to granular, with a deep cream to tawny-buff to pale cinnamon coloured red surface Produce abundant, symmetrical, ellipsoidal, thin-walled, verrucose, 4-6 celled macroconidia. 13 Varun C N

Trichophyton: 

Trichophyton Produces smooth walled Macroconidia and Microconidia. Macroconidia are thin walled and cigar-shaped. Microconidia may be pyriform 2-3μm or irregular in form. Some species rarely produce Macroconidia. The type species is T. tonsurans.

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Trichophyton mentagrophytes Colonies are generally flat, white to cream in colour, with a powdery to granular surface. Microconidia are hyaline, smooth-walled, and are predominantly spherical to subspherical in shape, however occasional clavate to pyriform forms may occur 15 Varun C N

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Trichophyton mentagrophytes var. quinckeanum 16 Varun C N

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Trichophyton rubrum Downy type Production of scanty to moderate numbers of slender clavate microconidia and no macroconidia Granular type Cigar shaped macroconidia of T. rubrum 17 Varun C N

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Trichophyton Agars 1 – 7 Georg and Camp devised a set of chemically-defined media for differentiation and identification of Trichophyton isolates based on specific vitamin and amino acid requirements. Trichophyton Agar 2, 3 and 4 are used with medium 1 to determine whether an isolate requires inositol, thiamine or both. 18 Varun C N

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Epidermophyton: 

Epidermophyton Characterized by large Macroconidia which are thin-walled, multi-cellular, club-shaped and clustered in bunches. Microconidia are not produced.

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Colonies are usually slow growing, greenish-brown or khaki coloured with a suede-like surface, raised and folded in the centre, with a flat periphery and submerged fringe of growth. Older cultures may develop white pleomorphic tufts of mycelium. A deep yellowish-brown reverse pigment is usually present. Microscopic morphology shows characteristic smooth, thin-walled macroconidia which are often produced in clusters growing directly from the hyphae. Numerous chlamydoconidia are formed in older cultures. No microconidia are formed. 22 Varun C N

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Macroconidia Chlamydoconidia 23 Varun C N

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Reference: 

Reference Mycology online- Adelaide university Trichophyton Agars 1 – 7, Difco website Dermatophytes in domestic animals, Francisco Javier Dermatophytes: Their taxonomy, ecology and pathogenicity, Mukoma F. Simpanya Form and function in the evolution of dermatophytes, Richard C. Summerbell, CLINICAL MICROBIOLOGY REVIEWS, Apr. 1995, p. 240–259.

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Varun C N 26 Thank you for your kind attention You can also follow me at my blog. Varuncnmicro.blogspot.com