Dermatophyte Test Medium

Dermatophyte Test Medium DTM - Teknofarma

Specific culture medium for:
Microsporum canis,
Microsporum gypseum,
Tricophyton mentagrophytes

Mycoses are very frequent skin diseases in dogs and cats.

Various methods can be used to diagnose them – e.g. A Wood’s lamp or trichoscopic examination – but the most important and most reliable is certainly the culture test.

A culture test is carried out by taking a skin sample from the infected area (hairs and scales) and placing it on a selective culture medium for the growth of dermatophytes (DTM medium). This contains:

  • antibiotics, which prevent the growth of contaminating bacteria and fungi other than dermatophytes
  • a colour indicator, which shows if the sample is positive. As the dermatophyte grows, it produces alkaline metabolites, thus causing the alkalinisation of the medium. As a consequence, the colour of the medium changes from orangey yellow to deep red.

DTM is a dermatophyte-specific culture medium for the diagnosis of fungal infections of the skin caused by Microsporum canis, Microsporum gypseum and Tricophyton mentagrophytes.

DTM consists of a transparent bottle containing a selective, orange-coloured culture medium which changes colour. If the culture medium changes to red within 2-10 days after placing the sample, it is diagnostic for the presence of pathogenic dermatophytes.



When taking a sample, it is essential to follow a few simple, yet particularly important rules:

  • use sterile tools (scalpels, tweezers, etc.)
  • take the sample from lesions that have not been treated with antifungal and/or disinfectant agents
  • choose smaller and more recent lesions
  • take the material (hairs and scales) both from the centre and the edges of the lesions. To make sure that the sample also contains a portion of the intrafollicular part of the hair, gradually pull in the direction of the hair.

Performing the test

  • Open the bottle by unscrewing the screw cap.
  • Place the sampled material (hairs and scales) on the surface of the culture medium without scratching it. Make sure that the proximal and/or intrafollicular part of the hair is in contact with the medium. In case of very long hairs, the distal part of the hair can be cut off and removed to facilitate inoculation.
  • Close the bottle by placing the cap on top of it, without screwing it in. Mark the sample with name, number, date or other relevant information.
  • Keep the test away from direct sunlight and at a temperature between 20 and 30 °C, or place it in a thermostat at 25 °C.
  • Starting 48 hours after inoculation, check the tests daily.

Reading and interpreting the results

Positive test for dermatophytes

Within 2 to 10 days since inoculating the culture medium, the colour changes from orangey yellow to red around the colony/colonies. The colonies can have different sizes, they look raised from the culture medium, have a cottony appearance and are whitish or cream-coloured.

Negative test for dermatophytes

Within 2 to 10 days since inoculating the culture medium, no colour change occurs. The presence of dark green, brown or black saprophytic colonies may be detected. Although the medium contains specific growth inhibitors, these colonies may develop because of a high pollution load in the inoculated sample.

After about 2-3 weeks since inoculation, and in the presence of saprophytic colonies, the medium may show a delayed change of colour and become red. However, this has no diagnostic relevance.

Negative test for dermatophytes, but indicative of candida

Within 1 to 4 days since inoculating the culture medium, no colour change occurs, but the early development of a flat, pearly-white, translucent or waxy-looking colony is observed.

After 6 or more days since the appearance of the colony, the entire culture medium might show a slight change in colour. However, this has no diagnostic relevance for the detection of dermatophytes.

The above mentioned times may vary depending on the fungal load of the sample and the incubation temperature of the test.

lampada di wood - Teknofarma
micosi gatto - Teknofarma

The tests must be kept away from light sources and at a temperature lower than 25 °C, or in refrigerator at 2-8 °C.

The presence of condensation inside the bottle is normal.

If correctly stored, the culture medium has a gelatinous texture, a smooth, homogeneous surface and is slanted.

The glass bottle and the airtight closure with aluminium cap ensure the optimal preservation of the culture medium.

If the culture medium inside the bottle looks dehydrated with a cracked or wrinkled surface, it is no longer usable.

The period of validity of the test is 30 days after the date of preparation.


DTM is available in three packages:

  • 2-test box
  • 12-test box
  • 24-test box.

The sale of DTM is reserved for veterinarians and health professionals.

You can buy DTM from veterinary wholesalers or directly from the manufacturing company.

For commercial offers on DTM, please contact commerciale@teknofarma.com


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