Microbiology · Molds and dermatophytes
Mucorales (Rhizopus, Mucor) !
- Fungus
- Exam priority: medium
Soil molds that invade vessels and destroy tissue very fast, above all in diabetic ketoacidosis: from the sinuses into the orbit and brain.
Updated 2026-11-01
Also called: mucormycosis, zygomycosis, black fungus
At a glance
- Shape
- Broad ribbon-like hyphae with few or no septa, branching at nearly right angles
- Family
- Mucoraceae and related families (Mucorales)
- Type
- Molds (filamentous fungi) of the order Mucorales
- Stain
- H&E, PAS and silver (GMS) on biopsy; calcofluor on direct exam
- Size
- Broad hyphae, about 6–25 µm
Morphology
- Broad, irregular hyphae, flattened like a ribbon
- Almost no septa (pauciseptate)
- Branching at close to 90°
- In culture, very fast cotton-like growth with sporangia
Transmission
- Inhaling spores from soil and decaying organic matter
- Inoculation into wounds, burns or trauma
- Rarely by ingestion
- Not spread from person to person
Reservoir: Soil, decaying plant matter, compost
Isolation precautions
What the care team adds to standard precautions.
- Standard
Virulence factors
- Invasion of blood vessels: thrombosis, infarction and black necrosis of tissue
- Exploits free iron: acidosis releases it from transferrin; deferoxamine acts as a siderophore for the fungus
- Thrives in acid, high-glucose conditions, which also impair neutrophils
Diseases it causes
- Mucormycosis: rhinocerebral (the classic form in diabetes), pulmonary, cutaneous, gastrointestinal and disseminated
- Diabetic ketoacidosis: the main setting for rhinocerebral mucormycosis Diabetic ketoacidosis →
Clinical picture
- Facial pain, nasal congestion with dark discharge and periorbital swelling in a decompensated diabetic
- Black eschar on the palate or turbinates
- Vision loss, ophthalmoplegia and cranial nerve palsies
- Very fast progression: hours to days
Diagnosis
- Urgent biopsy: broad ribbon-like, sparsely septate hyphae invading vessels
- Tissue culture (may be negative even when hyphae are seen)
- CT or MRI of sinuses and orbit to map the extent
- Galactomannan and beta-D-glucan do not detect Mucorales
Treatment
An emergency: wide surgical debridement, lipid amphotericin B as first line, and posaconazole or isavuconazole as alternatives or for step-down; correct the ketoacidosis and reduce immunosuppression. Voriconazole does not work against Mucorales.
Drug class only; doses and regimens are set by the clinician from the current guideline.
In Pharmacology:
Prevention
- Good diabetes control and prompt treatment of ketoacidosis
- Prudent corticosteroid use
- Care of wounds and burns contaminated with soil
Test yourself
Think of the answer, then tap the question to see it.
Who is the typical patient with rhinocerebral mucormycosis?
A person with diabetes in ketoacidosis (also transplant, neutropenia or iron overload).
What do Mucorales hyphae look like on biopsy?
Broad, ribbon-like, with few or no septa, branching at nearly right angles and invading vessels.
Why does ketoacidosis favour mucormycosis?
Acidosis frees iron from transferrin, which the fungus uses to grow, and impairs neutrophil function.
Which azole has no activity against Mucorales?
Voriconazole; posaconazole and isavuconazole are active.
What are the two pillars of mucormycosis treatment?
Urgent surgical debridement and lipid amphotericin B, together with correcting the underlying disease.
Related
Related conditions
← Back to the group: Molds and dermatophytes
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Mucormycosis Basics (CDC, 2024); Mucormycosis Risk Factors (CDC, 2024); Clinical Overview of Mucormycosis (CDC, 2024).
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Representative model, for educational purposes only.