Coccidioides immitis


Dimorphic at 25 and 37 degrees C. Hyphae are septate and hyaline. Conidiophores absent. Arthroconidia unicellular, rectangular to barrel shaped, often somewhat wider in diameter than the hyphae, alternating with empty cells (disjunctors); freed arthroconidia possess annular frills which are persistent remnants of the wall of the broken disjunctor. At 42 degrees C. on special media or at 37 degrees C. in infected tissue spherules (10-80um) containing endospores.


at 25 degrees C. and 37 degrees C.
Surface: Texture wooly to glabrous; White, sometimes beige, pink, cinnamon, yellow or brown on surface.
Reverse: Pale, sometimes orange, or pale to dark brown.
Growth Rate: Moderately rapid to rapid.


Coccidioides immitis is a dangerous fungus which should only be manipulated in culture in a biological safety cabinet in a containment laboratory. Cultures should only be grown in tubes, never on petri plates. Slide cultures should not be made. Its alternate arthroconidia with diameter slightly greater than the diameter of the hyphae are liberated by the lysis of the disjunctors and retain an annular frill at the ends. C. immitis is distinguished from Malbranchea by its capacity to produce spherules in special media at 42 degrees C. or in the tissues of animals infected experimentally. Currently, these techniques are little used in the clinical laboratory; they have been replaced by immunodiffusion tests (exoantigen) or by nucleic acid hybridization studies which are both safer and more rapid.


A soil saprobe found principally in certain parts of the southwestern United States and northern Mexico. Some endemic regions also found in South America. It can be isolated from the microbially depauperate soils of hot, semiarid regions, where its growth is favored by the low degree of competition from other soil microorganisms.


Cause of coccidioidomycosis, which is a highly infectious disease that may be an acute but benign, self-limiting respiratory disease or a chronic, malignant, sometimes fatal infection involving the skin, bone, joints, lymph nodes, adrenals, and central nervous system. It is endemic in the arid southwestern United States and in dry regions of Mexico, Central America, and South America.


Incubate at 25 degrees C. or 35 degrees C. for 7-14 days.


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.