Urease positive Fungi: Introduction, list of fungi and test procedure

Urease Positive Fungi: Introduction, List of Fungi and Test Procedure

Introduction of Urease Positive Fungi

Urease positive fungi can be differentiated on the basis of using urease agar slopes with 0.5% glucose. As you know, there are so many urease positive bacteria e.g. Proteus, Klebsiella, Helicobacter, Mogenella morganii, Yersenia and so on.

Similarly few fungi are also urease positive and they are-

Cryptococcus neoformans and
Trichophyton mentagrophyte.

Composition of Urease Agar Slopes with 0.5% Glucose for Fungi

For the differentiation of urease producing organisms.

Urease glucose broth base-

Urea broth base: 0.9 g

Glucose: 5 g

Distilled water: 450 ml

Add the urea broth base and glucose to the distilled water in a 500 ml beaker,
Dispense in 5× 90 ml amounts.
Autoclave at 115°C for 20 minutes.
When cool, label and store in the fridge.

Method to make slopes

40% Urea solution: 10 ml

Bacto agar: 3 g

Distilled water: 100 ml

Add 3 g of agar to 100 ml of distilled water in a 250 ml pyrex bottle.
Autoclave at 121°C for 15 minutes and place in 50°C water bath.
When cool add 90 ml of the urease broth with glucose and the 10 ml of 40% urea solution to agar and dispense in 3 ml aliquots and slope on racks.

Test Procedure for Urease Positive Fungi

5 days urease test help to differentiate T. mentagrophytes from T. rubrum. Tubes of urea agar are very lightly inoculated with the dermatophytes and held for 5 days at room temperature. Most isolates of T. mentagrophytes demonstrate urease production resulting in a color change. Most T. rubrum isolates are negative or require more than 5 days to give a positive reaction. Similarly, Cryptococcus neoformans as shown above image is positive after 3 days of incubation at 37°C.

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