Germ Tube Test for Candida: Principle, Procedure, Results and Interpretation 4.8/5 (15)

Germ tube test is the confirmatory test for Candida albicans. Germ tube formation was first reported by Reynolds and Braude and hence the germ tube test is also known as Reynolds-Braude Phenomenon. This is a rapid method for identifying and differentiating C. albicans from other Candida spp.

Germ Tube
Germ Tube

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.

Candida albicans in Gram Staining
Candida albicans in Gram Staining

Principle of Germ Tube Test:
Germ tubes are short outgrowth, 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 370C for 2-4 hours Candida albicans produce short, slender, tube like structures called germ tubes. 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 to human pooled serum.

Requirements:

  • Culture: Suspected Candida colonies from culture plate
  • 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

Procedure:

  1. Aliquot 0.5 ml (12 drops) of serum or media in a test tube.
  2. Make a light suspension of the suspect yeast colonies (by touching 1-2 large colonies or 3-4 smaller colonies with a sterile wooden applicator stick or loop) on serum.
  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 and cover with a coverslip.
  5.  Examine the wet mount microscopically (at 40X) for production of germ tubes (long tube-like projections extending out from the yeast cells).

    Candida albicans: Germ Tube Positive
    Candida albicans: Germ Tube Positive

Result and interpretation:

  • 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.

Limitations: 

  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.

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9 thoughts on “Germ Tube Test for Candida: Principle, Procedure, Results and Interpretation

  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. Tankeshwar Acharya

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      Reply

      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. jaffkumar@gmail.com

    - Edit

    Reply

    •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. prabha Sethuraman

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    Reply

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

     
    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.

         

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