Comparison of the Pathogenicity of the Yeast and Mycelial Phases of Blastomyces Dermatitidis

View More View Less
  • Department of Microbiology, Louisiana State University School of Medicine, New Orleans, Louisiana
Restricted access


Yeast- and mycelial-phase cells of Blastomyces dermatitidis were compared with respect to their capacity for invading the chorioallantoic (CA) membrane of embryonated chick eggs. Experiments were conducted at 31°C and at 37°C.

At 37°C, B. dermatitidis yeast cells penetrated into the mesoderm where they proliferated and produced microabscesses. Mycelial-phase cells inoculated on the CA membrane of embryos maintained at 31°C were confined to the ectoderm so long as the embryo remained viable and the integrity of the CA membrane was maintained.

The degree of initial exudative response to mycelial-phase cells was less than that noted with yeast. This difference in the degree of exudative reaction was particularly evident in experiments conducted at 31°C.

In experiments conducted at 37°C, mycelialphase cells began to convert to the yeast form within 24 hours after inoculation of CA membranes. The newly formed yeast cells subsequently penetrated into the mesoderm and produced microabscesses. Hyphae which failed to convert to yeast remained confined to the ectoderm and appeared to be undergoing degeneration.

From the work presented here, and a previous report by Baker,1 it appears that in animal tissue with a temperature of 37° to 39°C B. dermatitidis must convert to the yeast phase in order to survive and multiply.

Author Notes

Present address: 1412 Werner Park, Fort Campbell, Kentucky.