Primary subcultures ofHistoplasma capsulatum

Abstract

The colonial and micromorphology of 36 primary subcultures of H. capsulatum from various sources have been studied in depth. Most strains separate into 2 main types on the basis of colony appearance. The A or albino type with white aerial mycelium and smooth macroconidia and the B or brown type consisting almost solely of masses of tuberculate macroeonidia. The implications of this in identification and epidemiology are discussed. Several new or improved cytological observations are reported including racket hyphae, nuclei and nucleoli, gelatinous wall sculptures and perforate septa. Although much is being written (Ajello, 1967; Campbell, 1967; Nielsen, 1967) about the medical, serological, diagnostic and epidemiologic aspects of histoplasmosis and its etiological agent, Histoplasma capsulatum, little has been done systematically to characterize the morphology and cytology of the many strains which different investigators use. This often makes comparisons of results meaningless. It was therefore decided to study in depth as many primary isolates from as many sites and geographic areas as were available to me in a year period. Observations recorded here relate only to the macromorphology and cytology of the mycelial phase. Studies on the physiology, morphology and pathogenicity of the yeast phase are in progress and will be reported later. Only strains for which a complete history was available were used. They were received as isolated, in the plates or tubes of media planted usually with livers and spleens of mice inoculated with specimens from patients and nature, and only occasionally with specimens directly from the patient. As especially requested they were not subcultured before shipping. This seemed to be the only logical approach to the study of an organism as seemingly exasperating in its morphological and physiological variation as H. capsulatum if meaningful correlations were to be established among source, morphology, pathogenicity, antigenic properties and conversion ability.