Overview
Aspergillus niger is one of the most familiar molds in daily life. Its black, powdery colonies turn up on spoiling food and damp building materials, and it is one of the fungi most commonly found contaminating foods and feedstuffs, in soil, and in indoor environments.[1]
It is also one of the most important microorganisms in biotechnology. For decades it has been used to produce citric acid and food enzymes, and the U.S. Food and Drug Administration considers citric acid and many A. niger enzymes generally recognized as safe (GRAS).[2]
Medically, A. niger is best known as a cause of fungal ear infection (otomycosis). Lung infections are rare and occur mainly in people with severely weakened immune systems.[2]
Classification
- Phylum: Ascomycota
- Family: Aspergillaceae
- Genus: Aspergillus
- Section: Nigri (the "black aspergilli")
- Species: A. niger
A. niger belongs to a group of black-spored aspergilli. Based on molecular data, the only other common species closely related to it is A. tubingensis.[2] It is a different species from Aspergillus fumigatus, the main cause of serious aspergillosis.
Where Aspergillus niger Is Found
- Food. A. niger is one of the fungi most commonly encountered on foods and feedstuffs.[1] The black, sooty mold sometimes seen on onions and stored fruit is often this species.
- Soil and plant debris. It is a common soil fungus that breaks down organic matter.
- Indoors. In a study of more than 5,300 samples from moldy building materials, A. niger was associated with concrete and floor-related materials, together with other aspergilli, Chaetomium, and Mucor species.[3]
Health Significance
Ear infections (otomycosis)
Aspergillus and Candida species are the fungi most frequently isolated from people with otomycosis, a fungal infection of the outer ear canal.[4] An earlier safety review noted that A. niger ear infections occur particularly in tropical areas and may depend on mechanical damage to the skin barrier of the ear canal.[2]
Treatment of non-invasive otomycosis centers on careful cleaning of the ear canal and topical antifungals such as clotrimazole or miconazole. Oral triazole antifungals are essential for the rare invasive form, malignant fungal otitis externa, which can be complicated by mastoiditis and meningitis.[4]
Lung infections
Most invasive aspergillosis is caused by A. fumigatus, followed by A. flavus and A. terreus. A. niger is rarely reported as a cause of pneumonia.[5] One published case involved a 72-year-old woman with chronic obstructive pulmonary disease on long-term steroids. Her infection progressed despite antifungal treatment and required surgical removal of part of a lung. Calcium oxalate crystals in lung tissue are a classic clue to A. niger infection.[5]
Reported lung infections have occurred in severely immunocompromised patients.[2] Compared with other filamentous fungi, A. niger does not stand out as a particular problem for allergy or infection, though its spore dust should still be avoided.[2]
Mycotoxins
A. niger can produce two groups of potentially carcinogenic mycotoxins: fumonisins and ochratoxin A. The proportion of strains that do so has been debated:
| Study | Finding |
|---|---|
| Schuster et al., 2002 (review) | 3–10% of strains examined produced ochratoxin A under favorable conditions[2] |
| Frisvad et al., 2011 (180 strains) | Fumonisins in 81%, ochratoxin A in 17%, both in 10%[1] |
| Frisvad et al., 2011 (industrial strains) | Fumonisins in 83%, ochratoxin A in 33%, both in 26%[1] |
These figures reflect the ability of strains to make toxins in laboratory culture, not measured levels in food. The researchers recommended that industry use strains with inactive toxin gene clusters, or related species that do not produce these toxins.[1] For consumers, the practical takeaway is simple: discard visibly moldy food, especially soft foods where mold can spread below the surface.
Is Aspergillus niger "Black Mold"?
Because its colonies are black, A. niger is often called black mold. When people talk about toxic black mold in water-damaged homes, however, they usually mean Stachybotrys chartarum, a different fungus. Other common indoor molds include Cladosporium, Penicillium, and Chaetomium. See our guide on whether black mold is dangerous for more.
When to See a Clinician
See a clinician for ear itching, pain, discharge, or a blocked feeling that does not improve, and avoid putting cotton swabs or other objects in the ear canal. People with weakened immune systems, or with chronic lung disease on long-term steroids, should seek prompt care for cough, coughing up blood, chest pain, or fever.
This page is for educational purposes and is not medical advice. Consult a qualified healthcare provider about ear symptoms, lung symptoms, or mold exposure.