Mycology Review:

Identification of Common Dermatophytes Sandy Arduin, MT (ASCP)

Bruce Palma, MT (ASCP)

Mycology Unit

Bureau of Laboratories

Michigan Department of Community Health

This project was supported in part by Grant/Cooperative Agreement NumberU10/CCU523395-01 from the Centers for Disease Control and Prevention (CDC)

Its contents are solely the responsibility of Michigan Department of Community Health and do not necessarily represent the official views of CDC

Dermatophytes

Index Trichophyton rubrum Trichophyton mentagrophytes Hair Perforation Test Trichophyton tonsurans Trichophyton verrucosum Trichophyton terrestre Epidermophyton floccosum Microsporum canis Microsporum gypseum

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Macroscopic colony morphology descriptions are based on cultures grown on SAB agar. Colony morphology may vary on other culture media.

Microsporum nanum Differentiation TableTest Your KnowledgeUnknown 1Unknown 2Unknown 3Unknown 4Unknown 5Unknown 6

Trichophyton rubrum

Colony growth is slow to moderate, downy, white on the surface with a red to brown reverse.

Microconidia are club-shaped to pyriform and are formed along the sides of the hyphae.

Macroconidia are pencil-shaped to cigar-shaped.

Lab tests: hair perforation test negative, urease negative, growth at 37°C.

Infection is typically found on the feet, hands, nails, or groin.

Trichophyton mentagrophytesColony growth is moderately rapid, powdery to granular, white to cream colored on the surface with a yellowish, brown or red-brown reverse.

Microconidia are numerous, unicellular, round to pyriform and found in grape like clusters. Spiral hyphae are often present.

Macroconidia are multiseptate, club-shaped and often absent.

Lab tests: hair perforation test positive, urease positive, growth at 37°C.

Infection is typically found on the feet, hands, or groin, but can also be associated with inflammatory lesions of the scalp, nails, and beard.

Hair Perforation Test

Trichophyton mentagrophytes, Hair perforation test is positive.

Trichophyton rubrum, Hair perforation test is negative.

Perforations

Trichophyton tonsuransColony growth is slow, suede-like to powdery, white, beige, pale yellow to sulphur yellow on the surface with a yellow to dark brown reverse.

Microconidia are numerous, varying in shape and size (pyriform, club-shaped to balloon- shaped).

Macroconidia are rare. When present they are sinuous with smooth walls.

Lab tests: hair perforation test typically negative, urease positive, growth at 37°C. Growth is enhanced on thiamine.

Infections are primarily of the scalp. Occasionally the glabrous skin or nails are infected.

Trichophyton verrucosumColony growth is very slow, glabrous to lightly downy, white, sometimes yellow or grey on the surface without any characteristic pigment on the reverse.

Microconidia are club-shaped, but are rare or absent. Typically, chlamydospores in chains are seen.

Macroconidia have a “rat tail” appearance, but are rarely seen.

Lab tests: hair perforation test negative, urease negative, growth at 37°C. Growth is enhanced on media with thiamine and inositol, and is more rapid at 37ºC than at 25ºC.

Infection is more common on cattle or other farm animals. Infection in humans is typically found on the scalp, beard or glabrous skin.

Trichophyton terrestreColony growth is rapid, powdery to velvety, white to cream on the surface with a pale, slightly yellow reverse. Occasionally, isolates may have a pink, red-brown, or wine-colored reverse.

Microconidia are numerous, club-shaped, with a squared-off base, often borne on short pedicels.

Macroconidia are 2-8 celled and generally borne at right angles to the hyphae.

Lab tests: hair perforation test positive, urease positive and will not grow at 37°C.

This is a geophilic fungus, very common in soil. It can also be isolated from the fur of small mammals.

Epidermophyton floccosumColony growth is slow, powdery, with a yellow to khaki surface color and chamois to brown reverse.

Macroconidia are club shaped, with thin smooth walls and can be solitary or grouped in clusters. Chlamydospores are often produced in large numbers.

Microconidia are absent.

Lab tests: hair perforation test negative, urease positive, growth at 37°C.

Infections are commonly cutaneous, especially of the groin or feet.

Microsporum canisColony growth is rapid, downy to wooly, cream to yellow on the surface with a yellow to yellow- orange reverse.

Microconidia are club-shaped but typically are absent.

Macroconidia are fusoid, verrucose, and thick walled. They have a recurved apex and contain 5-15 cells.

Lab tests: hair perforation test positive and urease positive.

Infection in humans occurs on the scalp and glabrous skin. It is also a cause of ringworm in cats and dogs.

Microsporum gypseumColony growth is rapid, downy, becoming powdery to granular, cream, tawny-buff, or pale cinnamon on the surface with a beige to red-brown reverse.

Microconidia are moderately abundant and club-shaped.

Macroconidia are abundant, ellipsoidal to fusiform, sometimes verrucose, and thin walled. They typically contain 3-6 cells.

Lab tests: hair perforation test positive and urease positive.

Infection in humans is found on the scalp and glabrous skin; it is more frequently isolated from the soil and from the fur of small rodents.

Microsporum nanumColony growth is rapid, downy to powdery, white to buff on the surface, with a red-brown reverse.

Microconidia, if present, occur in small numbers.

Macroconidia are numerous, 1-3 celled, and have a characteristic pear or egg shape. Typically macroconidia are 2 celled. Conidia are solitary on the ends of short conidiophores.

Lab tests: hair perforation test positive and urease positive.

Infection is rarely transmitted to humans; it is the principal cause of tinea in pigs.

Hair Perforation Test

Urease Test

Growth at 37°C

Macro-conidia Micro-conidia Distinguishing Characteristics

Trichophyton rubrum

Negative Negative Positive Pencil shaped/cigar shaped

Club shaped to pyriform, along the sides of the hyphae

Red reverse pigment

Hair perf. test neg.

Club shaped microconidia

Trichophyton mentagrophytes

Positive Positive Positive Club shaped when present

Numerous

Unicellular to round in grape like clusters

Round microconidia in grape like clusters

Spiral hyphae

Trichophyton tonsurans

Usually (-)

Occasionally +Positive Positive Cylindrical to cigar

shaped and sinuous, if present

Numerous, varying in shape and size,

club shaped to balloon shaped

Microconidia varying in shape and size

Growth enhanced by thiamine

Trichophyton verrucosum

Negative Negative Positive “Rat-tailed” if present

Rare or Absent

Chlamydospores in chains typically seen

Chlamydospores in chains

Growth better on media with thiamine and inositol

Trichophyton terrestre

Positive Positive Negative 2-8 celled borne at right angles to

hyphae

Club shaped with squared-off base on

pedicels

Microconidia with squared-off base on short

pedicels

Epidermophyton floccosum

Negative Positive Positive Club shaped, often in clusters

Absent Khaki colored colony with brown reverse

Microconidia absent

Microsporum

canis

Positive Positive NA Fusoid, thick, rough walled with

recurved apex

Typically absent

Club shaped if present

Fusoid, rough walled macroconidia with

recurved apex

Microsporum gypseum

Positive Positive NA Ellipsoidal to fusiform, thin, Rough walled

Moderately abundant Club

shaped

Thin walled macroconidia

Tawny-buff granular colony

Microsporum nanum

Positive Positive NA Typically 2 celled Pear or egg shaped

Rough walled

Clavate when present

2 celled pear shaped macroconidia

Dermatophyte Differentiation

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Answer

Unknown 1

Colony growth is rapid, downy to wooly, cream to yellow on the surface with a yellow to yellow- orange reverse.

Answer

Unknown 2

Colony growth is moderately rapid, powdery to granular, white to cream colored on the surface with a yellowish, brown or red-brown reverse.

Answer

Unknown 3

Colony growth is rapid, downy to powdery, white to buff on the surface, with a red-brown reverse.

Answer

Unknown 4

Colony growth is very slow, glabrous to lightly downy, white, sometimes yellow or grey on the surface without any characteristic pigment on the reverse.

Growth is enhanced on media with thiamine and inositol, and is more rapid at 37ºC than at 25ºC.

Answer

Unknown 5

Colony growth is slow to moderate, downy, white on the surface with a red to brown reverse.

Answer

Unknown 6

Colony growth is rapid, downy, becoming powdery to granular, cream, tawny-buff, or pale cinnamon on the surface with a beige to red-brown reverse.

GlossaryAnthropophilic A fungus (dermatophyte) which grows preferentially on humans, rather than on animals or in soil.

Clavate Club-shaped.

Conidium A unicellular or multicellular fungal element which serves as an asexual reproductive structure.

Dermatophyte A mould belonging to the genera: Epidermophyton, Microsporum, Trichophyton; typically infecting skin, hair and nails.

Fusoid Spindle shaped; ellipsoidal with two tapered ends.

Glabrous Smooth, lacking hairs.

Geophilic A fungus (dermatophyte) which grows preferentially on substrates found in the soil, rather than on animals or humans.

Macroconidia The larger of two types of conidia produced by the same fungus. May be multicellular.

Microconidia The smaller of two types of conidia produced by the same fungus. Typically unicellular.

Onychomycosis Fungal infection of the nails.

Spiral hyphae Hyphae curved into a spiral. Typically seen in Trichophyton mentagrophytes, but may be seen in other dermatophytes as well

Verrucose Having many warts

Zoophilic A fungus (dermatophyte) which grows preferentially on animals, rather than on humans or in soil.

Bibliography

de Hoog, G.S., Guarro, J., Figueras, Gene & M.J. 2000. Atlas of Clinical Fungi, 2nd ed. Centraalbureau voor Schimmelcultures. Utrecht, The Netherlands.

Benecke, E.S., and Rogers, A.L. 1996. Medical Mycology and Human Mycoses. Star Publishing Company, Belmont, California.

Kane, Julius, Summerbell, Richard, Sigler, Lynn, Krajden, Sigmund, and Land, Geoffrey. 1997. Laboratory Handbook of Dermatophytes. Star Publishing Co., Belmont, CA.

Larone, Davise H. 1995. Medically Important Fungi, A Guide to Identification, 3rd ed., ASM Press, Washington, D.C.

McGinnis, M.R. 1980. Laboratory Handbook of Medical Mycology, Academic Press, New York, New York.

McGinnis, M.R., D'Amato, RF., Land, GA. 1982. Pictorial Handbook of Medically Important Fungi and Aerobic Actinomycetes. Praeger Publishing.

Murray, P.R., Brown, E.J., Pfallen, M.A., Tenover, F.C., Yolken, R.H., Manual of Clinical Microbiology, 7th Edition, ASM Press, Washington, D.C.

Rebell, Gerbert, Taplin, David. 1974. Dermatophytes, Their Recognition and Identification. University of Miami Press, Coral Gables, Florida.

Rippon, J.W., 1974. Medical Mycology The Pathogenic Fungi and The Pathogenic Actinomycetes. W.B. Saunders, Philadelphia, PA.

St-Germain, G., Summerbell, R. 1996. Identifying Filamentous Fungi, Star Publishing Company. Belmont, CA.