Saksenaea vasiformis

The genus Saksenaea is characterised by the formation of flask-shaped sporangia with columellae and simple, darkly pigmented rhizoids. Saksenaea vasiformis is the only known species and appears to have a world-wide distribution in association with soil. It is an emerging human pathogen (Holland, 1997) that is most often associated with cutaneous or subcutaneous lesions after trauma. Colonies are fast growing, downy, white with no reverse pigment made up of broad, non-septate hyphae typical of a zygomycetous fungus. Sporangia are typically flask-shaped with a distinct spherical venter and long-neck, arising singly or in pairs from dichotomously branched, darkly pigmented rhizoids. Collumellae are prominent and dome-shaped. Sporangiospores are small, oblong, 1-2 x 3-4 µm, and are discharged through the neck following the dissolution of an apical mucilaginous plug. RG-2 organism.

Key Features: zygomycete, unique flask-shaped sporangia, failure to sporulate on primary isolation media.

Culture and hyphae of Saksenaea vasiformis.

Sporangium of Saksenaea vasiformis.

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

Laboratory identification of some zygomycetous fungi, especially Apophysomyces elegans and Saksenaea vasiformis may be difficult or delayed because of the mould's failure to sporulate on the primary isolation media or on subsequent subculture onto potato dextrose agar. Sporulation may be stimulated by the use of nutrient deficient media, like Czapek Dox agar, cornmeal-glucose-sucrose-yeast extract agar, or by using the agar block method described by Ellis and Ajello (1982) and Ellis and Kaminski (1985).

Briefly, a small block of agar is cut from a well established culture grown on PDA and is placed in the centre of petri dish containing 1% agar in distilled water. After 21 days at 26C look for sporangium formation at the periphery of the petri dish.

Agar block method to induce sporulation of Saksenaea vasiformis.

Clinical significance:

Saksenaea vasiformis is a rare human pathogen that has also been associated with invasive lesions following traumatic implantation of the fungus and rhinocerebral, cutaneous and disseminated types of infection have also been reported. S. vasiformis appears to have a world-wide distribution in association with soil.

Mycosis: Zygomycosis

Further reading:

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

Ellis, D.H., and G. Kaminski. 1985. Laboratory identification of Saksenaea vasiformis: a rare cause of zygomycosis in Australia. Sabouraudia: J. Med. Vet. Mycol. 23:137-140.

Ellis, J.J., and L. Ajello. 1982. An unusual source of Apophysomyces elegans and a method of stimulating sporulation of Saksenea vasiformis. Mycologia 74:144-145.