ASPERGILLUS

SPECIES

Aspergillus brasiliensis formerly A. niger
Aspergillus clavatus
Aspergillus flavus
Aspergillus fumigatus
Aspergillus glaucus
Aspergillus nidulans
Aspergillus terreus
Aspergillus versicolor

MICROSCOPIC APPEARANCE

Hyphae are septate (2.5 - 8.0 micrometers in diameter); an unbranched conidiophore arises from a specialized foot cell. The conidiophore is enlarged at the tip, forming a swollen vesicle. Vesicles are completely or partially covered with flask-shaped phialides (formerly referred to as sterigmata) which may develop directly on the vesicle (uniseriate form) or be supported by a cell known as a metula (biseriate form). The phialides produce chains of mostly round, sometimes rough, conidia (2 - 5 micrometers in diameter).

MACROSCOPIC APPEARANCE

Surface: Initially white and then any shade of yellow, green, brown, or black, depending on species. Texture is velvety or cottony.
Reverse: White, goldish, or brown.
Growth Rate: Rapid, mature within 3 days; some species are slower growing.

DISTINGUISHING FEATURES

Aspergillus spp. is easily recognized by its conidiophores terminating in an apical vesicle and, at the opposite end, in a basal foot cell inserted into the supporting hyphae. Phialides are attached directly to the vesicle (uniserate) or an intervening cell called a metula (biseriate); these structures may cover the entire surface (columnar head); conidia in chains. The identification of species or species groups depends primarily on colony color and the form of conidial heads. The appearance of the species commonly isolated in the clinical laboratory is normally typical on Sabouraud Dextrose Agar or Potato Dextrose Agar. In reference works, descriptions are often of colonies grown on Czapek-Dox Agar.

HABITAT

Aspergillus appear to be cosmopolitan, saprobic fungi of solid (especially cultivated soils) and decomposing plant material. Airborne contaminant frequently encountered in the clinical mycology laboratory.

PATHOGENICITY

Members of the genus cause a group of diseases known as aspergillosis. The disease may be in the form of invasive infection, colonization, toxicoses, or allergy. Species of Aspergillus are opportunistic invaders, infecting carious sites in individuals with lowered resistance due to underlying-immunocompromising, debilitating disease and/or prolonged treatment with immunosuppressive drugs or antimicrobial agents. Aspergillus spp. are widespread in the environment and are commonly found as contaminants in cultures. Aspergillus spp. are a frequent cause of respiratory infection in birds; they are also occasionally a cause of mycotic abortion in certain mammals, in particular cattle and sheep.

RECOMMENDED MEDIA

Incubate at 25 degrees C. for 2-7 days.

REFERENCES

1. Hensyl, William R., et al. 1990. Stedman's Medical Dictionary , 25th ed. Williams & Wilkins, Baltimore, MD.

2. St. Germain, Guy and Summerbell, Richard, Ph.D. 1996. Identifying Filamentous Fungi , 1st ed. Star Publishing Company, Belmont, CA.

3. Larone, Davise H. 1995. Medically Important Fungi, A Guide to Identification . 3rd ed. American Society for Microbiology Press, Washington, D.C.

4. The Oxoid Vade-Mecum of Microbiology . 1993. Unipath Ltd., Basingstoke, UK.


102308mg