MICROSPORUM

SPECIES

MICROSCOPIC APPEARANCE

Hyphae septate. Conidiophores scarcely or not differentiated from vegetative hyphae; microconidia (microaleurioconidia) are unicellular, ovoid to club-shaped, and solitary. Macroconidia (macroaleurioconidia) are fusiform, with a thick or thin, echinulate wall, solitary, containing 2 to 15 cells; some species are typically sterile but may sometimes form macroconidia on suitable media.

MACROSCOPIC APPEARANCE

Surface: Texture glabrous, downy, or woolly; white, beige, cinnamon, yellow or rusty on surface.
Reverse: Pale white.
Growth Rate: Rapid to Slow.

DISTINGUISHING FEATURES

From a taxonomic point of view, Microsporum is distinguished from Trichophyton and Epidermophyton by its fusiform macroconidia with rough to echinulate walls. In practice, the identification of many species rests primarily on the appearance of the macroconidia, since the microconidia are not sufficiently distinctive to be useful for this purpose. Some species, however, produce few or no macroconidia. The production of macroconidia can sometimes be stimulated by cultivating isolates on lactritmel agar, autoclaved rice grains, Potato Dextrose Agar or Sabouraud Dextrose Agar containing 3 to 5% sodium chloride. In the absence of conidia, the colony appearance and certain physiological tests are used in identification.

HABITAT

Microsporum are cosmopolitan while others have geographically restricted distributions.

Microsporum includes anthrophilic, zoophilic, and geophilic species. Most infections in humans are acquired from infected dogs or cats.

Microsporum Characteristics of Selected Species
SPECIES Colony Growth Texture Growth Color
(surface/reverse)
Macro-
conidia
Micro-
conidia
Hair perforation Remarks M.
audouinii
Moderately rapid Felt-like, downy Whitish/salmon Fusoid,
deformed,
very rare

Absent or numerous Negative Poor growth
on rice grains
M. canis Rapid Downy, woolly White,
yellowish/orange
Fusoid,
apex recurved,
numerous

Moderately numerous Positive Good growth
on rice grains
M. cookei Moderately rapid Downy, powdery White,
yellowish/dark red
Fusoid,
numerous
Numerous Positive N/A M.
ferrugineum
Slow Glabrous Rusty to
white/rusty,
pale

Absent Absent Negative "Bamboo
hyphae"
M. gallinae Moderately rapid Downy White,
pinkish/red,
diffusible

Club-shaped,
rare or numerous
Rare or numerous Negative N/A M. gypseum Rapid Powdery Beige/brown,
yellowish
Fusoid,
symmetrical,
numerous

Moderately numerous Positive N/A M. nanum Moderately rapid Powdery White,
yellowish/red-brown
Ovoid,
2-celled,
numerous

Moderately numerous Positive Avoid confusing
with Trichothecium
M.
persicolor
Rapid Powdery Yellowish,
pink/red-brown
Fusoid,
club-shaped,
sometimes present

Numerous Positive Poor growth
at 37 o C.

PATHOGENICITY

The genus Microsporum includes some 17 species, of which 5 are primarily isolated from humans and 7 primarily from animals. Microsporum infects the skin and the hair, but seldom infects nails. Microsporum is known to be a causative agent for dermatophytosis, Cutaneous mycoses , Tinea capitis and Tinea corporis (ringworm).

RECOMMENDED MEDIA

Incubate at 25 degrees C. for 7-14 days.

REFERENCES

1. Hensyl, William R., et al. 1990. Stedman's Medical Dictionary , 25th ed. Williams & Wilkins, Baltimore, MD.

2. St. Germain, Guy and Summerbell, Richard, Ph.D. 1996. Identifying Filamentous Fungi , 1st ed. Star Publishing Company, Belmont, CA.

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

4. The Oxoid Vade-Mecum of Microbiology . 1993. Unipath Ltd., Basingstoke, UK.


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