Species of candida, commonly known as yeast, can cause infections in humans, ranging from vaginal infections, oral thrush and diaper rash to more serious and life-threatening infections of the blood, liver, spleen, brain or the respiratory tract. Most mild infections of candida can be identified at a clinician's office by visual examination. However, when in doubt, reliable tests are performed in the laboratory using patient samples from the site of infection such as skin scrapings, sputum, blood or pus.
Gram Stain
A small amount of patient sample is smeared on a glass slide and stained with dyes such as crystal violet and basic fuschin and observed under a microscope. Candida cells have a characteristic purple color and budding structure. According to the information published in Mackie and McCartney's Manual of Practical Medical Microbiology, the observation of yeast cells during gram staining is significant in normally sterile tissues and body fluids. However, the results are much less conclusive in contaminated material such as feces and sputum.
KOH Exam
KOH exam is another rapid test that can be performed at the physician's office and can provide a quick preliminary diagnosis of candida infections. Patient sample is placed in a liquid containing potassium hydroxide, or KOH, and observed under the microscope. The New York Times Health Guide states that KOH destroys all non-candida cells and makes it easier to detect the yeast cells. As with gram staining, a positive KOH test is significant in sterile tissues and body fluids only.
Culture
Small portions of the patient's sample are placed on a growth medium, which is a gel designed to support the growth of candida species, and is placed at 37 degrees Celsius overnight. The Mackie and McCartney's Manual of Practical Medical Microbiology states that yeasts pathogenic to humans appear as pasty, opaque, pale colored colonies with sweet smell reminiscent of ripe apples. These yeast colonies may be confirmed by emulsifying a portion of the colony into a dye called lactophenol cotton blue and observing the characteristic budding cells under a microscope.
Biopsy
Biopsy involves removal of a small portion of the patient's infected tissue using a needle. A representative portion of this tissue is then transferred to a drop of 20 percent KOH on a slide and observed under the microscope. The Mackie and McCartney's Manual of Practical Medical Microbiology recommends this test for complicated tissue infections of candida such as those of liver and spleen.
Magnetic Resonance Imaging (MRI)
MRI is a non-invasive method of taking pictures of the infected organs and, like biopsy, is used to diagnose serious candida infections of organs such as liver and spleen. The patient has to lie down on a narrow table and slide into the MRI scanner which uses powerful magnets and radio waves to take pictures of the infected organs.
And, although MRIs are non-invasive, in a study published in the October 1998 edition of the journal "Acta haematologica", Dr. S. Sallah has reported that when used in patients with high clinical suspicion for liver and spleen candida infections, MRI provides an effective alternative for liver biopsy or other invasive diagnostic procedures.
References
- "Mackie and McCartney's Practical Medical Microbiology"; J. G. Collee, A. G. Fraser, B. P. Marmion, A. Simmons; 1996
- New York Health Guide: Skin Lesion KOH Exam
- "Acta haematologica"; Diagnosis and monitoring response to treatment of hepatosplenic candidiasis in patients with acute leukemia using magnetic resonance imaging.; Sallah S, Semelka R, Kelekis N, Worawattanakul S, Sallah W; October 1998
