Comparison of Infection of Mice by Mycelial and Yeast forms of Blastomyces Dermatitidis

Abstract

Organisms causing human blastomycosis are regularly found in the yeast form in the lesions; and in the mycelial form when grown on artificial medium at room temperature. The mycelial form can be transformed into the yeast form by animal passage or merely by growing on blood agar at incubator temperature. Repeated mouse passage does not appear to enhance the virulence for mice of the causative organism.1 It is of interest to inquire whether the mycelial form is as infectious as the yeast form when equivalent dosages are given to No one knows whether man acquires either cutaneous or systemic forms of blastomycosis from the mycelial or the yeast form although the former source is the more probable. Mice can be caused to develop extensive abdominal and pulmonary lesions regularly by the intraperitoneal injection of the yeast form of some strains of Blastomyces dermatitidis. Will the mycelial form do the same? One might argue that the mycelial form would be encapsulated in the abdominal cavity, possibly by the omentum, and that pulmonary lesions would not occur. From the older literature one gathers that extensive animal lesions not produced with regularity, and it is not always clear what form of the organism was used or what dosage was employed. Spring2 noted that 20 days is the optimum time for the development of the disease in mice. Strains varied in ability to produce animal lesions. Death should not be expected. In mice there was a tremendous hyperplasia of yeast forms, and the tissue reaction was not effective. The dosage was not given. The injections used must have been of the mycelial form, however, since cultures kept at room temperature. Of 14 animals injected there were four instances of universal generalization; that is, multiple miliary blastomycetic abscesses in most of the organs, and both thoracic and abdominal.