DESCRIPTIONS OF MEDICAL FUNGI

Descriptions of Medical Fungi 175
Saksenaea vasiformis Complex
The genus Saksenaea is characterised by the formation of flask-shaped sporangia with
columellae and simple, darkly pigmented rhizoids. It is an emerging human pathogen
(Holland, 1997) that is most often associated with cutaneous or subcutaneous lesions
after trauma. Until recently, Saksenaea vasiformis was the only known species with a
worldwide distribution in association with soil. However S. vasiformis has recently been
split into three species; S. vasiformis, S erythrospora and S. oblongispora (Alvarez et
al. 2010b). All three species have been isolated from clinical samples, but as yet no
proven case reports have been published on the new species (de Hoog et al. 2015).
Saksenaea vasiformis Saksena
Morphological Description: Colonies are fast growing, downy, white with no reverse
pigment, and made up of broad, non-septate hyphae typical of a mucormycetous
fungus. Sporangia are typically flask-shaped with a distinct spherical venter and longneck,
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: Mucorales, unique flask-shaped sporangia, failure to sporulate on
primary isolation media.
Molecular Identification: ITS sequencing is required for differentiation of species
within the complex, and may be necessary to achieve identification in a timely manner
(Alvarez et al. 2010b, Walther et al. 2012, Halliday et al. 2015).
Comment: Laboratory identification of this fungus may be difficult or delayed because of
the mould’s failure to sporulate on primary isolation media or on subsequent subculture
onto potato dextrose agar. Sporulation may be stimulated by using the agar block
method described by Ellis and Ajello (1982), Ellis and Kaminski (1985) and Padhye
and Ajello (1988), although this may still take a period of days to weeks. Failure to
sporulate prohibits antifungal susceptibility testing.
The agar block method to induce sporulation
of Saksenaea spp. and Apophysomyces
spp.
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 26 O C sporangia might be formed at the
periphery of the petri dish.
Antifungal Susceptibility: S. vasiformis very limited data, due to poor sporulation
(Sun et al. 2002 and Australian national data); MIC µg/mL.
Antifungal Range MIC 90
Antifungal Range MIC 90
AmB 0.125-2 2 POSA 0.016-0.25 0.25
ITRA 0.016-0.03 0.03 VORI 0.5-4 4