How to Identify Aspergillus Niger

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Aspergillus colonies look something like this, but are blackish-yellow in color.
Aspergillus colonies look something like this, but are blackish-yellow in color. (Image: Jupiterimages/Photos.com/Getty Images)

Aspergillus niger, more commonly known as black mold, is a fairly common fungus with an extremely bad and well-earned reputation. This mold is a member of the fungal genus Aspregillus ("niger" being Latin for black), and can be responsible for a number of respiratory problems in the lungs, bronchus, sinus and ears. Fungal ear and lung infections are the the most common manifestation of Aspergullus exposure; infections are most likely to strike those with preexisting immunological disorders.

Things You'll Need

  • Mold-spore-rated dust mask and ear plugs
  • 5x-magnification magnifying glass
  • Microscope and glass sample plates

Identify the colonies visually. The mold you see with the naked eye is actually a colony of thousands of microscopic mushrooms. These colonies can range in size from a single mold spore to acres across, but are generally broken up into distinct patches and spots. A wall or flat surface infested with black mold will usually look as though it's been hit with a load of 20-gauge bird shot, peppered with countless yellow-black spots about the size of a pinhead. These spots will eventually coalesce to form a single black mass, but the outer parts will remain peppered.

Strap your mold mask on and put your ear plugs in and examine one of the individual colonies (spots) with a magnifying glass. The entire colony will look a bit "pixelated," made up of millions of tiny spots like one of Seurat's pointillist paintings. Under five to 10 times magnification, the individual spots will appear deep red-black in the center where the spore heads are the thickest. At its edges, the colony changes to yellow or white, depending on the specific strain of Aspergillus and the substrate.

Take a sample, put it on a glass sample slide and examine it under a microscope. Increase magnification until you can see the individual fungi. The individual Aspergillus fungi look like dandelions, with a transparent yellowish stem (called the metulae) that supports a dark red-brown head shot through with black lines (called the phialides), which radiate out from the center. On the tip of each phialide you'll find a transparent, yellowish-red, spherical spore.

Tips & Warnings

  • According to the Environmental Protection Agency, symptoms of lung-borne Aspergillus infection can mimic bronchitis or tuberculosis, and include chronic cough, difficulty breathing, chest pain and hemoptysis (coughing up blood). Aspergillus ear infections can cause severe ear pain, tinnitus (ringing in the ears), impaired hearing and inner-ear inflammation. Persons with a history of immuno-suppressive illness (low white blood cell count), high levels of naturally occurring adrenal corticosteriods and a history of taking cytotoxic antibiotics such as azathioprine are at the greatest risk of infection. Seek medical help immediately if you have any of these symptoms or any of the aforementioned risk factors in conjunction with black mold symptoms. Aspergillus produces oxalic acid, kojic acid and Malformin C, which can be fatal even in fairly small doses.

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