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Mold of the Week: Aspergillus

Colony Description:

  • Colonies usually growing rapidly, powdery, white, green, yellowish, brown or black in colour.

Spore (Conidia) Description:

  • Conidia produced in dry chains, forming columns (columnar) or diverging (radiate), from flask-shaped phialides, 1-celled, smooth-walled or ornamented, (sub)hyaline or pigmented. Cells with extremely thick walls (Hülle cells) or sclerotia may be present.


Diagram of Aspergillus sp.

Microscopic view of Aspergillus under the microscope (400x)

Habitat outdoors:

  • outside air, water, food items, soil, plant debris, rotten vegetation, manure, sawdust litter, bagasse litter, animal feed, bark chippings, on animals. Not readily identified or isolated on spore traps of outside air samples in Saint Lucia, Saint. Vincent and the Grenadines and Dominica.




Habitat Indoors:

  • Every surface: wooden furniture, walls, glass etc.

Potential Health Effects:


Allergenic

Common.

  • Type I allergies (hay fever, asthma).

  • Type III hypersensitivity pneumonitis: Humidifier lung, Malt worker's lung, Compost lung, Wood trimmer's disease, Straw hypersensitivity, Farmer's lung, Oat grain hypersensitivity, others.

  • Other: allergic fungal sinusitis

Pathogenic

Respiratory, invasive, cutaneous, ear, and corneal disease. Severe, invasive disease is usually associated with immunosuppressed hosts because many species grow at 37°C (body temperature) meaning they are thermotolerant and their one-celled, dry, hydrophobic conidia are easily inhaled.


e.g.

  • A. flavus and A. fumigatus are frequent causative agents of pulmonary aspergillosis, either allergic, or invasive or a combination of the two

  • A. niger and A. terreus, are relatively commonly isolated as secondary invaders in cases of bacterial otitis externa;

  • cerebral infections from many other species

Toxigenic

Toxins are chemical components which are capable of causing diseases and death. Below are some of the Aspergillus species and the toxins they produce. Some of the toxins listed below are potent carcinogens (cancer-causing agents):

  • A. flavus: aflatoxin B1 & B2, cyclopiazonic acid, kojic acid

  • A. fumigatus: ergot alkaloids, fumigaclavines, gliotoxin, fumigatoxin, fumigillin, fumitremorgens, helvolic acid, tryptoquivaline tremorgens, verruculogen.

  • A. niger: malformin C, oxalic acid.

  • A. ustus: austocystins.

  • A. versicolor: aspercolorin, averufin, cyclopiazonic acid, sterigmatocystin, versicolorin.


References:

  1. G. S. de Hoog et al (2018) Atlas of Clinical Fungi, http://atlas.clinicalfungi.org/AtlasOnline//protected/index.xhtml?index.html , Accessed: September 9, 2019.

  2. EMLAB P&K (2019) Aspergillus sp. https://www.emlab.com/resources/fungal-library/aspergillus-sp/ Accessed: September 9, 2019.

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