You are here: 
text zoom : S | M | L
Printer Friendly Version
Further Enquiries

School of Molecular & Biomedical Science
The University of Adelaide
AUSTRALIA 5005

Contact:
Dr David Ellis
Email


Microsporum sp.

Teleomorph: Arthroderma sp.

Microsporum species form both macro- and microconidia on short conidiophores. Macroconidia are hyaline, multiseptate, variable in form, fusiform, spindle-shaped to obovate, ranging from 7 to 20 by 30 to 160 um in size, with thin- or thick- echinulate to verrucose cell walls. Their shape, size and cell wall features are important characteristics for species identification. Microconidia are hyaline, single-celled, pyriform to clavate, smooth-walled, 2.5 to 3.5 by 4 to 7 um in size and are not diagnostic for any one species.

The separation of this genus from Trichophyton is essentially based on the roughness of the macroconidial cell wall, although in practice this may sometimes be difficult to observe. Seventeen species of Microsporum have been described (Rippon, 1988) however only the more common species are included in these descriptions:

Microsporum audouinii

Microsporum canis

Microsorum canis var. distortum

Microsporum canis var. equinum

Microsporum cookei

Microsporum ferrugineum

Microsporum fulvum

Microsporum gallinae

Microsporum gypseum

Microsporum nanum

Microsporum persicolor

The teleomorph states of all Microsporum species have been ascribed to the genus Arthroderma.   Nannizzia is now considered to be a synonym of Arthroderma.  Mating studies are not practical for the clinical mycology laboratory and identifications should be based on the anamorphic state.

It is essential to observe macroconidia when identifying species of Microsporum. Strains of M. canis often do not produce macroconidia and/or microconidia on primary isolation media and it is recommended that sub-cultures be made onto polished rice grains to stimulate sporulation. These non-sporulating strains of M. canis are often erroneously identified as M. audouinii and it is surprising just how many laboratories have difficulty in differentiating between M. canis and M. audouinii.

 

MIC data is limited.  Antifungal susceptibility testing of individual strains is recommended.

Antifungal MIC ug/mL Antifungal
MIC ug/mL
Range
MIC90
Range
MIC90
Griseofulvin
0.125-2
1
Amphotericin B
0.03-8
1-2
Itraconazole
0.01-4
0.125
Fluconazole
0.05->64
>64
Terbinafine
0.01-16
0.06
Voriconazole
0.007-1
0.5

 

Clinical significance:

The genus Microsporum contains a number of important species that are the principle causative agents of animal and human dermatophytoses [tinea and ringworm].

Further reading:

Rebell, G., and D. Taplin. 1970. The Dermatophytes. 2nd. revised edition. University of Miami Press, Coral Gables, Florida. USA.

Rippon, J.W. 1988. Medical Mycology. 3rd Edition. W.B. Saunders Co., Philadelphia, USA.