Germ Tube Test: Principle, Procedure, Results

Germ tube test is a screening test for the presumptive identification of Candida albicans. Candida dubliniensis can also form germ tubes and Candida tropicalis can produce pseudohyphae that closely resemble germ tubes.

Germ tube
Germ Tube

Germ tube formation was first reported by Reynolds and Braude and hence the germ tube test is also known as Reynolds-Braude phenomenon.

Buds and pseudo-hyphae can be distinguished from germ tubes by the constricted attachment at the point of origin. Germ tubes don’t show constriction at the point of origin.

Principle of Germ Tube Test

Germ tubes are short outgrowths, non-septate germinating hyphae. They are ½ the width and 3 – 4 times the length of the cell from which they arise. When cells of Candida are incubated in serum at 37°C for 2-4 hours, Candida albicans and Candida dubliniensis produce short, slender, tube-like structures called germ tubes.

Characteristics morphology of Candida albicans

A germ tube appears as a short lateral extension from the yeast cell and does not have a constriction (septum) where it meets the yeast cell or any constriction at the septum along the tube.

The formation of germ tubes is associated with increased synthesis of protein and ribonucleic acid. Various media like fetal bovine serum may be used as a substitute for human pooled serum.


  • Culture: Suspected Candida colonies from sabouraud dextrose agar (SDA).
    SDA is the best medium to isolate yeasts for germ tube production; sheep blood agar is an acceptable substitute
  • Reagent: Serum (human, sheep, fetal bovine) or other commercially produced media for germ tube testing
  • Others: Test tubes, loop or wooden applicator, Pasteur pipettes, slides, cover slips.
Candida albicans: Germ Tube Positive
Candida albicans: Germ Tube Positive

Quality Control

The following yeasts should be included each time the test is performed.

  1. Germ tube positive, C. albicans ATCC 14053
  2. Germ tube negative, Candida tropicalis ATCC 66029


  1. Lightly touch a yeast colony with a wooden applicator stick.
  2. Suspend the yeast cells in an appropriately labeled tube of fetal bovine serum (make a light suspension).
  3.  Incubate the tube for 2-3 hours in a 35 – 37°C incubator.
  4. Place a drop of the suspension on a slide using a Pasteur pipette.
  5. Place a coverslip over the suspension.
  6.  Examine the wet mount microscopically (at 40X) for the presence or absence of germ tubes.

Result and interpretation

Positive germ tube test: A short hyphal (filamentous) extension arising laterally from a yeast cell with no constriction at the point of origin is identified as C.albicans or C. dubliniensis. Some C. tropicalis isolates produce pseudohyphae that require careful observation to discriminate from those of C. albicans.

A minimum of five germ tubes should be observed before calling an organism positive, because rare tubes may be produced by other species. Growth at 45°C separates C. albicans from Candida dubliniensis.

Difference between pseudohyphae and germ tube

Negative germ tube test: No hyphal extension arising from a yeast cell or a short hyphal extension with constriction at the point of origin. A constriction where the lateral extension meets the yeast cell is produced by pseudohyphae or budding cells.


  1. Candida tropicalis may produce pseudo-germ tubes after 3 hrs of incubation but they show constriction at the point of origin.
  2. Too heavy inoculum will inhibit germ tube formation.

References and further readings

  1. Sudbery, P. E. (2011). Growth of Candida albicans hyphae. Nature Reviews Microbiology, 9(10), 737–748.
  2. Sudbery, P. E. (2001). The germ tubes of Candida albicans hyphae and pseudohyphae show different patterns of septin ring localization. Molecular Microbiology, 41(1), 19–31.
  3. Clinical Microbiology Procedures Handbook, Fourth Edition. (2016). American Society of Microbiology.

Acharya Tankeshwar

Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. As an asst. professor, I am teaching microbiology and immunology to medical and nursing students at PAHS, Nepal. I have been working as a microbiologist at Patan hospital for more than 10 years.

11 thoughts on “Germ Tube Test: Principle, Procedure, Results

  1. Thank-you very much for your wonderful description about germ tube….

    Let me ask you one doubt , about Isoplater in Microbiology.
    My question is. “From which area the Isoplater will start it’s streaking in an agar plate ?” I mean in which area the Isoplater will put the first inoculum on a plate..

    1. Hello Rajesh
      in our hospital laboratory we use manual streaking “streak plate method” and never used Isoplater so far. So i am not in the position to give you hands on tips regarding its usage and methodology. If you have not checked it earlier, you may get relevant information about Isoplater in this website.

  2. thank you for this nice article. I have a question, why is it necessary to observe germ cells microscopically after 2 hours of incubation?

  3. •Positive Result: A short hyphal (filamentous) extension arising laterally from a yeast cell with no constriction at the point of origin. May be confirmed as C.albicans
    •Negative Result: No hyphal extension arising from a yeast cell or a short hyphal extension with constriction at the point of origin.

    this is wrong
    acaually its opposite…

  4. Hi thanks you for this usefull blog myself Dr. Prabha working as lecturer in college
    . I need protocol for isolation of auxotrophic mutants. Thanks

  5. Why serum is used in germ tube test what is the function of serum in germ tube test??

    1. If a person was exposed to syphilis a month ago and was treated but did the test again and the antibodies are still positive , where else his VDRL/RPR and TPHA are negative. Can the antibody be transmitted to his/her partner through sex?

      1. Yes syphilis comes under sexually transmitted diseases which means it can be transmitted via sexual contact. Also instead of giving attention to positive reaction you must give attention to titre values whether they are increasing or decreasing.

  6. thank you for these information, but please what is the reference of positive result of germ tube test ?? bcz i need it to mention it in my thesis.

  7. Why serum is used in germ tube test what is the function of serum in germ tube test??

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