In vitro production of the spherule phase of Coccidioides immitis.

The in vitro growth of the spherule (sporangium) phase of Coccidioides immitis has posed a problem of prime interest in the study of the disease coccidioidomycosis. The fungus is dimorphic in that it has a cultural, or saprophytic, phase in which growth consists of mycelium and arthrospores, and a tissue or parasitic phase consisting of thick-walled nonbudding spherules (sporangia) varying in size from 20 to 80 , in diameter. Endospores measuring 2 to 5 ,u in diameter are developed in the mature spherules by cleavage planes, released into the tissues by rupture of the spherule wall, and serve as a means of reproduction and dispersal. The freed endospores enlarge and develop into the characteristic endospore-containing spherules. The physiological requirements for the production of the tissue phase are not known, although studies have been made concerning the developmental stages of spherules in the tissues of mice, along with their relation to host reaction (Tarbet, Wright, and Newcomer, 1952). In vitro production of the spherule phase has been achieved with some degree of success by several investigators by means of special media (Baker and Mirak, 1941; Burke, 1951; Burke, Salvin, and Gerhoff, 1952; Brueck and Buddingh, 1951; Conant and Vogel, 1954; Lack, 1938; MacNeal and Taylor, 1914; Moore, 1941; Newcomer, Wright, and Tamblyn, 1952; Vogel and Conant, 1952 a, b). These special media provided no freedom from the presence of the mycelial phase and resulted in the production of the vegetative phase accompanied by relatively few spherules.