Identification of Medically Important Fungi.

Identification of Zygomycetes.

Subcutaneous zygomycosis is generally caused by traumatic implantation and lesions vary considerably,
but include plaques, pustules, ulcerations, deep abscesses and ragged necrotic patches. In the
immunocompetent host, lesions usually remain localised around the site of inoculation and generally
respond well to local debridement and Amphotericin B treatment. However, in the debilitated patient,
zygomycosis is the most acute and fulminate fungal infection known.

 The disease typically involves therhino-facial-cranial area, lungs, gastrointestinal tract, skin, or less commonly other organ systems. It isoften associated with acidosis diabetes, malnourished children, severely burned patients and otherdiseases such as leukemia and lymphoma, immunosuppressive therapy, or use of cytotoxins and corticosteroids.

The infecting fungi have a predilection for invading vessels of the arterial system, causing embolization and subsequent necrosis of surrounding tissue.


Two orders, the Mucorales and the Entomophthorales contain genera and species of medical
importance. In general, fungi in the order Mucorales cause the more severe forms of disease with most
species belonging to the genera Rhizopus, Absidia, Rhizomucor, Mucor and Apophysomyces.
Rhizopus oryzae is the most frequent infectious agent reported, followed by R. microsporus var.
rhizopodiformis, Absidia corymbifera and Rhizomucor pusillus. These four species account for more
than 80% of culture proven cases of zygomycosis. Other mucoraceous species reported less frequently
include R. microsporus var. microsporus, Mucor ramosisimus, M. circinelloides, M. indicus,
Apophysomyces elegans, Cunninghamella bertholletiae and Saksenaea vasiformis. Basidiobolus
ranarum and Conidiobolus coronatus are the principle species of the Entomophthorales that cause
human disease, predominantly of the nasal mucosa and subcutaneous tissue.

Key features for identification include:
·  Coenocytic, mostly non-septate hyphae.
·  Zygospore morphology in homothallic strains, however most isolates are heterothallic, ie zygospores
are absent, therefore identification is based primarily on sporangial morphology. This includes the
following:

1. Arrangement and number of sporangiospores.
2. Sporangial shape and colour.
3. Presence or absence of columellae and apophyses.
5. Presence or absence of rhizoids
.
·  Growth temperature studies are also useful ie 35, 40, 45OC.
·  Tease mounts are best, use a drop of 95% alcohol as a wetting agent to reduce air bubbles.
·  May need to induce sporulation in isolates of Saksenaea vasiformis and Apophysomyces elegans
by using Czapek-dox agar or water agar.