Mycology Review: Identification of Common Dermatophytes

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Mycology ReviewIdentification 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

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Dermatophytes
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Index

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

• Microsporum nanum
• Differentiation Table
• Test Your Knowledge
• Unknown 1
• Unknown 2
• Unknown 3
• Unknown 4
• Unknown 5
• Unknown 6

Double click on any of the words listed above to
go directly to the slide on that organism. To
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click on the return button. You must be in slide
show mode to use these functions. Macroscopic
colony morphology descriptions are based on
cultures grown on SAB agar. Colony morphology
may vary on other culture media.
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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 37C.
• Infection is typically found on the feet, hands,
  nails, or groin.

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Trichophyton mentagrophytes

• Colony 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 37C.
• Infection is typically found on the feet, hands,
  or groin, but can also be associated with
  inflammatory lesions of the scalp, nails, and
  beard.

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Hair Perforation Test
Trichophyton mentagrophytes, Hair perforation
test is positive.
Trichophyton rubrum, Hair
perforation test is negative.
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Trichophyton tonsurans

• Colony 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 37C.
  Growth is enhanced on thiamine.
• Infections are primarily of the scalp.
  Occasionally the glabrous skin or nails are
  infected.

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Trichophyton verrucosum

• Colony 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 37C. 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.

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Trichophyton terrestre

• Colony 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 37C.
• This is a geophilic fungus, very common in soil.
  It can also be isolated from the fur of small
  mammals.

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Epidermophyton floccosum

• Colony 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 37C.
• Infections are commonly cutaneous, especially of
  the groin or feet.

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Microsporum canis

• Colony 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.

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Microsporum gypseum

• 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.
• 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.

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Microsporum nanum

• Colony 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.

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Dermatophyte Differentiation Table
Hair Perforation Test Urease Test Growth at 37C 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
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Test Your Knowledge
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Answer
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Unknown 1
Colony growth is rapid, downy to wooly, cream to
yellow on the surface with a yellow to yellow-
orange reverse.
Answer
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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
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Unknown 3
Colony growth is rapid, downy to powdery, white
to buff on the surface, with a red-brown reverse.
Answer
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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
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Unknown 5
Colony growth is slow to moderate, downy, white
on the surface with a red to brown reverse.
Answer
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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.
Answer
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Glossary
Anthropophilic 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.
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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.