Aspergillus niger: Introduction, Pathogenicity, Laboratory Diagnosis and Treatment

Aspergillus niger

Introduction of Aspergillus niger

Aspergillus niger is one of the most common and easily identifiable species of the genus Aspergillus, with its white to yellow mat later bearing black conidia. This species is very commonly found in aspergillomas and is the most frequently encountered agent of otomycosis (A. niger is one of the most common causes of otomycosis (fungal ear infections), which can cause pain, temporary hearing loss, and, only in severe cases, damage to the ear canal and tympanic membrane also. Some strains of Aspergillus niger have been reported to produce potent mycotoxins called ochratoxins and it also produces the orobol. It is also a common laboratory contaminant and comes under risk group (RG)-1 organism.

Scientific Classification of A. niger

  • Kingdom: Fungi
  • Kingdom: Fungi
  • Division: Ascomycota
  • Class: Eurotiomycetes
  • Order: Eurotiales
  • Family: Trichocomaceae
  • Genus: Aspergillus
  • Species: Aspergillus niger

Other medically important common species are-

Aspergillus flavus

Aspergillus fumigatus

Aspergillus nidulans and 

Aspergillus terreus

Pathogenicity of Aspergillus niger

Aspergillosis: It is a granulomatous, narcotizing, and cavity disease of the lung. often with hematogenous spread to other organs.

Manifestation

  1. Otomycosis and keratitis
  2. Toxicity from ingestion of fungal contaminated foods.
  3. Allergic manifestation
  4. Colonization of fungus in the various body cavities and debilitated tissues
  5. The invasive granulomatous disease of the lung with inflammation and necrosis
  6. A systemic disseminated disease that is usually fatal if not treated-increased incidence has been seen in
  • Leukemia
  • Diabetic patient
  • AIDS
  • Renal transplantation
  • Cardiac  transplantation

Laboratory Diagnosis of Aspergillus niger

Specimens: The selection of specimens depends on the site of infection.

  1. Sputum (lung disease, aspergillosis)
  2. sinus drainage
  3. Bronchial washing (lung disease, aspergillosis)
  4. Ear discharge (otomycosis)

Direct smear examination of Aspergillus niger

Culture

  • Sabouraud  dextrose agar (SDA)

  • One at 37°C and another 25°C  if necessary for up to 28 days.
  • Note: Culture correlation with direct smear examination is important because Aspergillus species are common laboratory contaminants.
  • Six consecutive morning samples are required out of which should show the same fungal growth in 50% sample.

Colony characteristic 

  • Velvety texture
  • Mold type growth
  • Pigmentation- black

Morphology of Aspergillus niger

Lacto  phenol cotton blue (LPCB) preparation

  • Conidiophore length: 1.5-3.0 mm
  • Vesicle width: 45-75 μm
  • Phialides: Biseriate
  • Color of conidia: Black
  • Diameter of conidia: 4.5-5.0 μm

Other Methods :

  • Skin test
  • Agar gel diffusion:

Aspergilloma: 3-4 bands (100%)

ABPA: 1-3 bands (50-75%)

Asthma: 1 band (50%)

Treatment of Aspergillus niger

Following drugs are used to treat this etiological agent-

  • Amphotericin B
  • Itraconazole
  • Voriconazole
  • Posaconazole
  • Anidulafungin
  • Caspofungin

Further Reading

  1. Medical Mycology. Editors:  Emmons and Binford, 2nd ed 1970, Publisher Lea and Febiger, Philadelphia.
  2. Rippon’s JW: Medical Microbiology. The pathogenic fungi and the Pathogenic Actinomycetes. 3rd ed 1988 Publisher WB Saunder co, Philadelphia.
  3. Clinical Microbiology Procedure Handbook Vol. I & II, Chief in editor H.D. Isenberg, Albert Einstein College of Medicine, New York, Publisher ASM (American Society for Microbiology), Washington DC.
  4. A Textbook of Medical Mycology. Editor: Jagdish Chander.  Publication Mehata, India.
  5.  Practical Laboratory Mycology. Editors: Koneman E.W. and G.D. Roberts, 3rd ed 1985, Publisher Williams and Wilkins, Baltimore.
  6. Description of Medical Fungi-David Ellis, Stephen Davis, Helen Alexiou, Rosemary Handke, Robyn Bartley
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