Microbiology Laboratory

GERM TUBE TEST

Written by MicroDok

AIM: To identify Candida albicans from fungal cultures as an aid in the diagnosis of Candidiasis.

MATERIAL/APPARATUS: Fungal culture, glass slide, cover slip, microscope, lactophenol cotton blue, Bunsen burner, inoculating loop, water bath or incubator, micro – pipette, test tube, test tube rack, horse serum or human serum, Pasteur pipette.

METHOD/PROCEDURE:

  1. Using a micro – pipette, pipette or transfer 0.5 ml (500 µl) of human/horse serum into a sterile test tube.
  2. Inoculate a portion of the fungal culture into the serum in the test tube using a sterile inoculating loop.
  3. Place the test tube containing both the fungal culture and the serum in a water bath or incubator at 35 – 37oC for about 2 – 3 hours.
  4. Transfer a drop of the serum – fungal culture to a glass slide using a Pasteur’s pipette.
  5. Cover the preparation with a cover slip.
  6. Examine the prepared slide under the microscope using the ×10 and ×40 objective lens. Make sure that the condenser iris of the microscope is sufficiently closed in order to get a good contrast. A drop of lactophenol cotton blue stain can also be added to the preparation if desired in order to stain the yeast cells for a proper/clear view.

REPORTING OF THE RESULT:

Look out for germ tubes i.e. sprouting/growing yeast cells that have tube – like outgrowth. If found, report the culture as: Candida albicans isolated.   But if these sprouting yeast cells are not seen, report the culture as: yeast other than C. albicans isolated.

NOTE: Only C. albicans and C. dubliniensis (a rarer oral pathogen) can produce germ tubes under the above described conditions. Other species of the genius Candida are germ tube negative under the above conditions, and thus require further tests to identify them.

Candida albicans is yeast which falls under the genus of fungi known as Candida. Several species of Candida are capable of causing candidiasis in humans. Candida species are members of the normal flora of the skin, mucous membranes, and gastrointestinal tract of humans. The indiscriminate administration of antibiotics in humans can further increase the amount of Candida in our intestinal tract, and they can enter the circulation by crossing intestinal mucosa, and become systemic. Candida vaginitis is a common infection experienced by women during pregnancy. Candida infections are opportunistic mycoses, occurring in debilitated people i.e. persons whose immune systems are weak or compromised as a result of a prior infection or something else like stress. Candida infections of the mouth and oesophagus are most common in people who have HIV infections.  The infection can be treated by the administration of antifungal drugs like amphotericin B, nystatin or fluconazole. Avoiding disturbance to the normal balance of microbial flora and host defenses of the body is the most important preventive measure for candidiasis.

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MicroDok

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