Effect of physico-chemical environment of spherulation of Coccidioides immitis in a chemically defined medium.

Coccidioides immitis undergoes a completely different type of growth in vivo from that in vitro. The parasitic form, or spherule, appears in animal tissue as a non-budding, spherical structure 20 to 80 ,u in diameter with a thick, refractile, double wall, and is filled witlh numerous small endospores 2 to 5 ,u in diameter. The saprophytic form appears in laboratory media as mycelium with branching, septate hvphae which fracture into numerous thick-walled, rectangular, spherical, or ellipsoidal arthrospores 2 to 4 ,u in diameter. Observation of the parasitic form of C. i7mnitis in solid or semi-solid complex media has been reported by several authors. AMacNeal and Taylor (1914) observed multiplication of spherules in infected pus when added to ascitic fluid or gelatinized horse serum containing sterile kidney slices. Lack (1938) noted development of spherules from arthrospores inoculated into Hall tubes containing glucose broth and partially coagulated egg albumin. Baker and MIrak (1941) observed the development of spherules in a variety of solid media when active growth had ceased as a result of drying of the media. Burke (1951) reported the appearance of spherules in a partially defined solid medium containing coconut milk. Conant and Vogle (1954) observed spherules in cultures transferred to Saboraud's medium following exposure to "Tween 80." Lubarsky and Plunkett (1955) were able to produce spherules in Tyrode's solution, supplemented with chick-embryo extract and serum and aerated periodically with measured amounts of oxygen and carbon dioxide. This laboratory was the first to report production of spherules in a chemically defined liquid medium (Converse, 1955). The work reported below represents further studies on the formation of spherules in a chemically defined liquid medium (figures 1 to 6). The following factors were investigated: the total concentration of nutrients in the medium, the hydrogen ion concentration of the medium, the temperature, aeration, and exposure to light during incubation, and the preparation of inoculum.