Two-step method for isolating Cryptococcus species complex from environmental material using a new selective medium.

Cryptococcosis is an opportunistic infection caused by the Cryptococcus species complex. An outbreak of cryptococcosis caused by Cryptococcus gattii (AFLP6/VGII) in North America has indicated the need for studies of this organism and its environmental niche. Difficulties in isolating the Cryptococcus spp. because of the overgrowth of filamentous fungi onto culture media and its low fungal population size under natural conditions limit studies of these pathogenic yeasts. We designed a selective medium that inhibits the growth of environmental filamentous fungi but does not inhibit that of Cryptococcus cells. After enrichment in acidified YPD media and inoculation onto selective media, Cryptococcus cells in brown-coloured colonies were isolated from environmental materials. This two-step method is useful for isolating environmental members of the Cryptococcus species complex, which is essential for further studies involving diversity and the microbe-environment relationship of this yeast.