Effect of temperature on the intracellular growth of Histoplasma capsulatum.

The rate and form of growth of Histoplasma capsulatum within histiocytes derived from homothermic and poikilothermic animals, and incubated at 25, 30, and 37 C, are described. The generation time of the fungus in mouse cells incubated at 37 and 25 C was 11 and 24 hr, respectively. Blastospore formation was progressively retarded in cells at 25 C, and this retardation was accompanied by germination of some of the blastospores. The generation time of the fungus in mouse cells incubated at 30 C was the same as it was at 37 C. Germ tube formation was not a prominent feature of intracellular growth at 30 C. The rate of growth of H. capsulatum within frog histiocytes at 30 and 25 C was slower than it was in mouse cells at the same temperatures. Some loss of frog histiocytes in cultures incubated at 37 C prevented accurate estimation of the rate of growth of the fungus at this temperature. Growth of H. capsulatum in frog histiocytes kept at 25 C was progressively retarded, and the retardation was accompanied by germination of the yeasts. Yeast-phase growth predominated in fish histiocytes incubated at 30 C, whereas germ tubes were formed within such cells incubated at 25 C. Cell survival of fish histiocytes was relatively poor in culture, and no estimates of rate of growth of the fungus within these cells were made.