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

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Dr David Ellis
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Rhizomucor pusillus

Synonym: Mucor pusillus

The genus Rhizomucor is distinguished from Mucor by the presence of stolons and poorly developed rhizoids at the base of the sporangiophores and by the thermophilic nature of its 3 species: R. miehei, R. pusillus and R. tauricus. All 3 of these species are potential human and animal pathogens and were originally classified in the genus Mucor. Rhizomucor variabilis as described by de Hoog et al. (2000) is not thermophilic and is probably a degenerate culture of Mucor hiemalis (Voigt et al., 1999).  Rhizomucor pusillus is cosmopolitan and both R. miehei and R. pusillus have been reported as pathogens to humans and animals, the latter to a greater extent.

This thermophilic zygomycete is readily recognizable by its characteristic compact, low (2-3 mm high), grey to greyish brown colored mycelium and by the development of typical sympodially branched, hyaline to yellow-brown sporangiophores (8-15 um in diameter), always with a septum below the sporangium. Sporangia are globose (40-60 um in diameter), each possessing an oval or pear-shaped columella (20-30 um), often with a collarette. Sporangiospores are hyaline, smooth-walled, globose to subglobose, occasionally oval (3-5 um), and are often mixed with crystalline remnants of the sporangial wall. Chlamydoconidia are absent. Zygospores are rough-walled, reddish brown to black, 45-65 um in diameter and may be produced throughout the aerial hyphae in matings between compatible isolates. Temperature growth range: minimum 20-27C; optimum 35-55C; maximum 55-60C.  RG-2 organism.

Rhizomucor pusillusRhizomucor pusillus
Sporangiophores, columellae and primitive rhizoids of Rhizomucor pusillus.

 

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

Antifungal
MIC ug/mL
Antifungal
MIC ug/mL
Range
Range
Itraconazole
0.03-0.25
Amphotericin B
0.06-0.25
Voriconazole
2-16
Posaconazole
0.06-0.25

 

Clinical significance:

Rhizomucor pusillus is a rare human pathogen, causing pulmonary, disseminated or cutaneous types of infection. It is more often associated with animal disease. Rh. pusillus has a world-wide distribution and is commonly associated with compost heaps.

 

Mycosis: Zygomycosis

Further reading:

Domsch, K.H., W. Gams, and T.H. Anderson. 1980. Compendium of soil fungi. Volume 1. Academic Press, London, UK.

Ellis, D.H. 1997. Zygomycetes. Chapter 16 In Topley and Wilson's Microbiology and Microbial Infections. 9th edition Edward Arnold London pp247-277.