DERMATOPHYTE TEST MEDIUM (DTM)
|Cat. no. J107||Sabouraud Dextrose (SabDex) Agar with Chloramphenicol and Gentamicin / DTM, 15x100mm Biplate, 15ml/15ml||10 plates/bag|
|Cat. no. L27||Dermatophyte Test Medium, 10ml Vial, 7.5ml Slant||20 vials/box|
|Cat. no. X15||Dermatophyte Test Medium, 50ml Hardy Flask™, 12ml||20 flasks/box|
Hardy Diagnostics Dermatophyte Test Medium (DTM) is a selective and differential medium recommended for the cultivation and isolation of pathogenic dermatophytic fungi.
Dermatophyte Test Medium is a modification of a commercial formulation made by Taplin in 1969.(6-8) Nitrogenous and carbonaceous compounds essential for microbial growth are provided by soy peptone. Dextrose serves as the energy source for metabolism. Chloramphenicol acts as a broad spectrum antimicrobic which inhibits a wide range of gram-positive and gram-negative bacteria. Cycloheximide is added to inhibit saprophytic fungi. Phenol red, the pH indicator, is affected by the presence of dermatophytes (Epidermophyton, Microsporum, and Trichophyton spp.), which all produce alkaline metabolites. Production of alkali results in the medium changing from yellow-orange to red in color.
Other organisms that may grow on the medium can be recognized as non-dermatophytes by their color and colony morphology. Bacteria and certain yeast can grow on this medium showing characteristic white or creamy bacteria like colonies. Contaminating saprophytes can turn Dermatophyte Test Medium from its yellow-orange color to red, but can be ruled out due to the green to black hyphae produced. Dermatophytes typically produce white aerial hyphae.
Ingredients per liter of deionized water:*
|Papaic Digest of Soybean Meal||10.0gm|
Final pH 5.6 +/- 0.2 at 25ºC.
* Adjusted and/or supplemented as required to meet performance criteria.
STORAGE AND SHELF LIFE
Storage: Upon receipt store at 2-8ºC. away from direct light. Media should not be used if there are any signs of deterioration (shrinking, cracking, or discoloration), contamination, or if the expiration date has passed. Product is light and temperature sensitive; protect from light, excessive heat, moisture, and freezing.
Specimen Collection: Infectious material should be submitted directly to the laboratory without delay and protected from excessive heat and cold. If there is to be a delay in processing, the specimen should be inoculated onto an appropriate transport medium and refrigerated until inoculation. Consult listed references for information on specimen collection.(1-5)
Method of Use: The medium should be brought to room temperature, and the agar surface should be dry prior to inoculation. Once received by the lab, the specimen should be inoculated directly onto the medium by pressing the specimen lightly into the surface of the agar. Alternatively, a small amount of fungus may be placed on the agar surface if subculturing from another culture medium. A control medium, Sabouraud Dextrose Agar (Cat. no. L40), may be inoculated in parallel.(9) Incubate media at room temperature (15-30ºC.), aerobically, for up to fourteen days. Examine media daily and observe for development of a red color change in the medium. Most pathogenic dermatophytes will produce a color change in three to six days.
INTERPRETATION OF RESULTS
Media should be examined daily for up to fourteen (14) days.
Positive: Appearance of white aerial hyphae and red color around the fungal growth is positive for the presence of dermatophytic fungi.
Negative: Growth, without a color change to red, indicates that the organism is probably not a dermatophyte. Further biochemical and/or serological testing is recommended for complete identification.
If growth appears on the control medium (Sabouraud Dextrose Agar) and no growth appears on DTM, the organism is not a dermatophyte. Colonies with green or black hyphae is not typical of dermatophytes even though the media may turn red.
This medium is more useful as a general screening test, as opposed to an identification medium.
False-positive reactions may result, if interpretations are made beyond 14 days of incubation. An alkaline reaction will eventually be produced by most non-dermatophytic fungi that are capable of growing on this medium.
If the dormant area of an infection is cultured, false-negative reactions may arise.
The caps of inoculated media must be kept loose to assure optimal recovery of dermatophytes.
A color change in the medium may be produced by certain strains of yeast. A characteristic white, creamy, bacteria-like colony will be produced by these organisms and thus allow differentiation from dermatophytic fungi.
If the specimen is heavily contaminated, saprophytic fungi may result in a color change on the medium.(9) Some of these organisms may be recognized by their dark green to black hyphae; white aerial hyphae is exhibited by dermatophytes.
MATERIALS REQUIRED BUT NOT PROVIDED
Standard microbiological supplies and equipment such as loops, other culture media, swabs, applicator sticks, incinerators, and incubators, etc., as well as serological and biochemical reagents, are not provided.
|Test Organisms||Inoculation Method*||Incubation||Results|
|G||4-7 days||15-30°C||Aerobic||Growth; white colonies and a red color change develops in the medium surrounding the colonies|
|A||24hr||15-30°C||Aerobic||Growth; small white colonies and no color change in the medium|
|G||up to 7 days||15-30°C||Aerobic||Inhibited|
User Quality Control
Dermatophyte Test Medium (DTM) should appear clear to slightly opaque, and yellow-orange in color.
1. Anderson, N.L., et al. Cumitech 3B; Quality Systems in the Clinical Microbiology Laboratory, Coordinating ed., A.S. Weissfeld. American Society for Microbiology, Washington, D.C.
2. Jorgensen., et al. Manual of Clinical Microbiology, American Society for Microbiology, Washington, D.C.
3. Tille, P., et al. Bailey and Scott's Diagnostic Microbiology, C.V. Mosby Company, St. Louis, MO.
4. Isenberg, H.D. Clinical Microbiology Procedures Handbook, Vol. I, II & III. American Society for Microbiology, Washington, D.C.
5. Koneman, E.W., et al. Color Atlas and Textbook of Diagnostic Microbiology, J.B. Lippincott Company, Philadelphia, PA.
6. Rebell, E., and Taplin. 1970. Dermatophytes, 2nd ed. University of Miami Press, Miami.
7. Taplin, D. 1965. J. Invest. Der.; 45:545.
8. Taplin, D., et al. 1969. Arch. Derm.; 99:203.
9. Campbell, M.C., and J.L. Stewart. 1980. The Medical Mycology Handbook, John Wiley & Sons, New York.
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