Yeasts

• Blastoschizomyces
• Candida
• Cryptococcus
• Loboa loboa
• Malassezia
• Rhodotorula
• Saccharomyces
• Trichosporon

Identification.

Yeast-like fungi may be basidiomycetes, such as Cryptococcus neoformans or ascomycetes such as Candida albicans.

1. Ensure that you start with a pure culture; streak for single colony isolation if necessary.

2. Germ Tube Test: lightly inoculated 5 ml of serum, containing 0.5% glucose and incubated at 35oC for 2-3 hours. 

• Positive = Candida albicans or Candida dubliniensis.
• Negative or from HIV positive patient = perform assimilation tests.

3. For the identification of germ tube negative yeasts, morphological (Dalmau plate culture), physiological and biochemical tests are essential.

Dalmau Plate Culture:  To set up a yeast morphology plate, dip a flamed sterilized straight wire into a light inoculum (sterile distilled water suspension) and then lightly scratch the wire into the surface of a cornmeal/tween 80, rice/tween 80 or yeast morphology agar plate, then place a flamed coverslip onto the agar surface covering the scratches.  Dalmau morphology plates are examined in situ using the lower power of a microscope for the presence of pseudohyphae which may take up to 4-5 days at 26oC to develop.  C. albicans also produces characteristic large, round, terminal, thick-walled vesicles (often called chlamydoconidia).  The key features to remember are to use a light inoculum and to scratch the surface of the agar with the wire when inoculating.