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Interpretation of Growth Patterns on Cornmeal Agar

Observing the microscopic morphology of yeast colonies after inoculation to cornmeal agar with Tween 80 is helpful in confirming the identification of a given species that has been presumptively determined by one of the automated or kit systems. Cornmeal Agar is used to distinguish the various species of Candida and other yeasts through examination of pseudohyphae, blastoconidia, chlamydoconidia, and arthroconidia.

After incubation, the agar plate is placed on a microscope stage and examines for growth, first examining under low power (10X), and then proceeding to the high dry (40X) objective.

Initial observations of the cornmeal agar will reveal whether or not the isolate produces pseudohyphae or hyphae.

  • The presence of pseudohyphae and blastoconidia suggests the genus Candida. All Candida species, with the exception of Candida (Torulopsis) glabrata, produce pseudohyphae when grown on cornmeal agar.
  • Yeasts that produce blastospores only include Candida glabrata, Cryptococcus, Rhodotorula, and Saccharomyces.
  • The presence of true hyphae indicates the presence of Trichosporon, Blastoschizomyces capitus, or Geotrichum.