Germ Tube Test
The germ tube test for Candida albicans is a simple and quick laboratory test used to identify Candida albicans based on its ability to form germ tubes—short, filamentous projections—when incubated in serum at 37°C for 2-3 hours.
Table of Contents
Principle of the Germ Tube Test
Candida albicans produces germ tubes (early hyphal extensions) under favorable conditions, such as:
Temperature: 37°C (human body temperature)
Nutrient-rich environment: Serum (usually fetal bovine serum or human serum)
Other Candida species (e.g., Candida tropicalis, Candida glabrata) do not form germ tubes under these conditions, making this test highly specific for C. albicans.
Reagents
Human serum A small volume to be used as a working solution may be stored at 2 to 8⁰C. Stock solution can be dispensed into small tubes and stored at -20⁰C.
Materials Required
Fresh yeast colony (from Sabouraud dextrose agar or CHROMagar)
Sterile serum (fetal bovine serum or human serum)
Incubator (37°C)
Microscope slides and coverslips
Light microscope
Step-by-Step Method
Prepare the Serum Mixture:
Place 0.5 mL of sterile serum in a test tube.
Emulsify a small portion of a pure yeast colony in the serum to create a slightly turbid suspension.
Incubation:
Incubate the mixture at 37°C for 2-3 hours.
Microscopic Examination:
After incubation, place a drop of the mixture on a glass slide and cover it with a coverslip.
Examine under a light microscope (40X magnification) for the presence of germ tubes.
Interpretation
| Observation | Examples |
|---|---|
| Positive Results : Germ tubes present (tube-like extensions without constrictions at the origin) | Candida albicans and Candida dubliniensis |
Negative Results : No hyphal extension from yeast cells OR Short hyphal extension with constriction at the origin. | C. tropicalis , C. glabrata and other non-albicans Candida species |
Precaution
C. tropicalis may form pseudohyphae which may be falsely interpreted as germ tubes.
Frequently Asked Questions
Can other Candida species produce germ tubes?
Rarely, Candida dubliniensis may also form germ tubes, leading to false positives. However, this species is less common than C. albicans.
What is the difference between germ tubes and pseudohyphae?
Germ tubes: Filamentous extensions without constrictions at their origin.
Pseudohyphae: Chain-like structures with constrictions between cells (seen in other Candida species).
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