Dermatophyte test medium

Dermatophyte Test Medium (DTM) is a specialized culture medium used in the field of dermatology and microbiology to isolate and identify dermatophytes, which are a type of fungi that cause skin infections known as dermatophytosis. These infections are commonly referred to as ringworm or tinea.

Composition

DTM is composed of a nutrient base that supports the growth of dermatophytes, along with indicators and inhibitors. The medium typically contains:

• Sabouraud dextrose agar as the nutrient base.
• Cycloheximide to inhibit the growth of non-dermatophyte fungi.
• Chloramphenicol to inhibit bacterial growth.
• Phenol red as a pH indicator.

The presence of phenol red allows for the detection of dermatophyte growth by a color change in the medium. Dermatophytes metabolize the nutrients in the medium, leading to an alkaline reaction that changes the color of the medium from yellow to red.

Procedure

To perform a dermatophyte test using DTM, the following steps are typically followed:

1. Sample Collection: A sample is collected from the infected area of the skin, hair, or nails using a sterile instrument. 2. Inoculation: The sample is inoculated onto the surface of the DTM. 3. Incubation: The inoculated medium is incubated at a temperature of 25-30°C for up to 14 days. 4. Observation: The medium is observed for growth and color change. A positive result is indicated by the growth of colonies and a color change to red.

Interpretation

A positive DTM result suggests the presence of dermatophytes. However, further identification of the specific species may require additional tests, such as microscopic examination or molecular techniques.

Applications

DTM is widely used in clinical laboratories for the diagnosis of dermatophytosis. It is a valuable tool for veterinarians and dermatologists in identifying the causative agents of fungal infections in both humans and animals.

Limitations

While DTM is effective in isolating dermatophytes, it has limitations:

• False positives can occur due to the growth of non-dermatophyte fungi that also cause a color change.
• Some dermatophytes may not grow well on DTM, requiring alternative methods for confirmation.

Related pages

• Dermatophytosis
• Fungal culture
• Microbiology
• Sabouraud agar