CRITERION™ DERMATOPHYTE TEST MEDIUM (DTM)

Cat. no. C5570 CRITERION™ Dermatophyte Test Medium 82.6gm
Cat. no. C5571 CRITERION™ Dermatophyte Test Medium 500gm
Cat. no. C5572 CRITERION™ Dermatophyte Test Medium 2kg
Cat. no. C5573 CRITERION™ Dermatophyte Test Medium 10kg

INTENDED USE

Hardy Diagnostics CRITERION™ Dermatophyte Test Medium (DTM) is a selective medium recommended for the isolation and cultivation of dermatophytic fungi.

This dehydrated culture medium is a raw material intended to be used in the making of prepared media products, which will require further processing, additional ingredients, or supplements.

SUMMARY

CRITERION™ 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. Gentamicin and Chlortetracycline act as a broad spectrum antimicrobics that inhibit 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.

FORMULA*

Gram weight per liter: 41.8gm/L
Soy Peptone 10.0gm
Dextrose 10.0gm
Cycloheximide 0.5gm
Phenol Red 0.2gm
Gentamicin 0.1gm
Chlortetracycline 0.1gm
Agar 20.0gm

Final pH 5.6 +/- 0.2 at 25ºC.

* Adjusted and/or supplemented as required to meet performance criteria.

STORAGE AND SHELF LIFE

Store the sealed bottle(s) containing dehydrated culture medium at 2-30ºC. Dehydrated culture medium is very hygroscopic. Keep lid tightly sealed. Protect dehydrated culture media from moisture and light. The dehydrated culture media should be discarded if it is not free-flowing or if the color has changed from its original beige.

Store the prepared culture media at 2-8ºC.

PRECAUTIONS

METHOD OF PREPARATION FOR DEHYDRATED CULTURE MEDIA

1. Suspend 41.3gm of the dehydrated culture media in 1 liter of distilled or deionized water. Stir to mix thoroughly.

2. Heat to boiling to dissolve completely.

3. Sterilize in the autoclave at 121ºC. for 15 minutes.

4. Cool to 45-50ºC.

PROCEDURE AND INTERPRETATION OF RESULTS

For information on procedures and interpretation of results, consult listed references or refer to the prepared media Instructions for Use (IFU) for Cat. No. X15.

LIMITATIONS

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-dermatophyte 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 autoclaves, incinerators, and incubators, etc., are not provided.

QUALITY CONTROL

Test Organisms Inoculation Method* Incubation Results
Time Temperature Atmosphere
Trichophyton mentagrophytes
ATCC ® 9533**
G 4-7 days 15-30°C Aerobic Growth; white colony with red color change in media on reverse
Candida albicans
ATCC ® 10231
A 24hr 15-30°C Aerobic Growth; small white colonies
Aspergillus brasiliensis
formerly A. niger
ATCC ® 16404**

G 7 days 15-30°C Aerobic Partial to complete inhibition; no color change
Escherichia coli
ATCC ® 25922
B 24hr 35°C Aerobic Partial to complete inhibition
Staphylococcus aureus
ATCC ® 25923
B 24hr 35°C Aerobic Partial to complete inhibition
Pseudomonas aeruginosa
ATCC ® 27853
B 24hr 35°C Aerobic Partial to complete inhibition

** Recommended QC strains for User Quality Control according to the CLSI document M22 when applicable.

User Quality Control

Physical Appearance

CRITERION™ Dermatophyte Test Medium powder should appear homogeneous, free-flowing, and beige in color. The prepared media should appear opaque, and yellow-orange in color.

REFERENCES

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.


ATCC is a registered trademark of the American Type Culture Collection.

052316gr