Efficacy of seed-based media for the mould-yeast conversion of Blastomyces dermatitidis.

The efficacy of 20 seed-based media is reported for the in vitro mould-yeast conversion of Blastomyces dermatitidis, employing pharmamedia agar, peptone glucose agar, glucose agar and water agar as controls. The mould-yeast conversion varied significantly according to the culture medium, fungal strains and incubation period (p less than 0.01). Garden-pea, chick-pea, cow-pea, soybean, peanut, green gram, French bean, lentil, okra and cottonseed converted all of the 7 B. dermatitidis test strains after 5 days of incubation at 37 degrees C. Although the efficacy of many of these seed media was found to be at par with pharmamedia agar - a commercial cottonseed embryo-derived protein, garden-pea seed agar is adopted because of the wider availability and low fat content of this seed. The recommended composition of the medium comprises 2% aqueous seed extract, 2% glucose and pH 6-7. Only nigerseed and sunflower seeds failed to support the conversion of B. dermatitidis. Of the control media, peptone glucose agar, glucose agar and water agar did not support the conversion of 2 of the B. dermatitidis test strains. The mechanism underlying variable mould-yeast conversion of B. dermatitidis on seed-based media is not clearly understood. However, most of the seeds supporting excellent mould-yeast conversion are known for their high protein content. The conversion was apparently not affected by the fat content of the seeds or by incorporation of glucose in the medium.