Used to check for capsules Cryptococcus and Rhodotorula both produce capsules. Rhodotorula have reddish pigmented colonies and C. neoformans loses its capsule the longer its in culture
Germ Tube Test
Add yeast to human or bovine serum. Incubate at 37 deg for 2 hours and 45 min. Examine mixture for germ tube production. 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.
Chlamydospore is a thick walled intercalary or terminal cell. Characteristic structure of C. albicans 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
Inoculate malt agar slant or V8 juice agar slant with yeast. Incubate room temp Examine every 48-72 hrs for 2-3 wks with a wet prep. Some ascospores take 6 weeks.
Flood slide with carbolfuchsin and steam gently for 2-3 min. 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
Inoculate Christensen's agar slant Incubate at room temp for 3-4 days Positive is cherry red
Organisms that are Urease positive
Cryptococcus and Rhodotorula. Occasionally C. krusei, C. humicola and some Trichosporon species
Not needed routinely to identify Candida species if technologist is familiar with morphology of species when examined on chlamydospore agar 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
Carbohydrate Assimilation Test
Checks which sugars can be assimilated by different species. 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
Nitrate Assimilation Test
Largely supplanted by the rapid nitrate test 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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