Sunday 13 June 2010

Aspergillus niger

(Fillamentous fungi)
Subgenus: Circumdati, Section: Nigri

This fungus was a bit of a challenge to photograph as it matured so quickly that conidia were often well dispersed when I was prepared to photograph the culture. It was difficult to find really good examples of the vesicles bearing metulae, phialides bearing intact conidial spores. Both adhesive tape preparations and slide cultures were studied.

Ecology; Ubiquitous, worldwide distribution, commonly found in mesophilic environments. One of the most common of the fungi in soil, rotting fruit & plant matter as well as many indoor environments. A.niger may be found as a common laboratory contaminant.

Macroscopic; Rapidly growing on Saboraud-Dextrose Agar starting with a white to yellowish felt-like mat of mycelia, quickly turning black as conida develop the pigment aspergillin during maturation. Reverse remains white to pale in colour.

Aspergillus niger on Sabouraud-Dextrose Agar 72 hrs at 30C
Black pigment from conidia maturing from center of colony
(click on photo to enlarge for better viewing)

Microscopic; Septate, hyaline (clear) hyphae. Conidiophores (Stipes) are long (400-3000 µm) with spherical vesicles at the apex measuring 30-75 µm. Aspergillus niger is biserate - metulae just about cover the entire surface from which the phialides extend. Conidia are globose, brown to black in colour, measure 3.5-4.5 µm in diameter and have a rough surface.

Large vesicle at end of broken conidiphore bearing metulae & phialides with black pigmented conidia already dispersed. Adhesive tape preparation was too disruptive in capturing structures intact. (LPCB X400)

Ditto (LPCB X400)
(Click on photos to enlarge for better viewing)

Aspergillus niger (LPCB X400)

Pathogenicity; not tremendously pathogenic however has been implicated in aspergillosis particularly in immunocompromised patients. Has also been isolated from ear infections (otomycosis), often as a secondary invader, establishing itself after/on top of a bacterial infection.

Industry; A.niger produces a number of useful enzymes which have been utilized by industry in the production of a variety of products such as citric acid. The possibility of A.niger being capable of producing mycotoxins remains controversial.

Treatment; Studies on the susceptibility of A.niger to antifungal agents remain inadequate. Isolates should be tested individually if therapy is warranted. Voriconizole as been shown to be effective in documented cases as well as Itraconazole and Amphoterecin B.

Intended as Aspergillus niger computer wallpaper (1024 X 768) when posted.
(click on photo to enlarge for better viewing)

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