Last Modified: 2012-04-26
Cryptococcus and Rhodotorula both produce capsules. Rhodotorula have reddish pigmented colonies and C. neoformans loses its capsule the longer its in culture
C. albicans produce germ tubes (98%) after 2 hr 45 min.
After 3 hours C. stellatoidea produces germ tubes.
C. albicans and C. stellatoidea can be differentiated using sucrose assimilation test.
Use chlamydospore agar plate, scarify the agar and streak over the top. Add coverslip
Use C. albicans as a control
Incubate room temp for 12-24 hours
Examine for Chlamydospores under low power
Incubate room temp
Examine every 48-72 hrs for 2-3 wks with a wet prep. Some ascospores take 6 weeks.
Wash and destain with 95% ethyl alcohol containing 1% HCl
Counterstain with aqueous methylene blue for 1-2 min. Ascospores will be red and vegetative cells blue
Incubate at room temp for 3-4 days
Positive is cherry red
Occasionally C. krusei, C. humicola and some Trichosporon species
Make Mcfarland 1 std
Inoculate each fermentation tube with .3 ml tighten caps incubate at room temp for 14 days. Positive fermentation is recorded for production of gas only
McFarland Std 4
Flood agar (yeast nitrogen base and brom cresol purple) use 1 ml. Allow to dry
Place sugar impregnated discs on plate
Incubate at 30deg C for 24-48 hours Color change from purple to yellow is positive for utilization
Known positive Cryptococcus albidus and Known negative Cryptococcus neoformans
Nitrate assimilation tests are only run on yeasts that are urease positive with negative fermentation after 24 hours
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