Dermatophyte test medium

Dermatophyte Test Medium (DTM) is a specialized agar medium used in Microbiology and Dermatology for the selective culture of dermatophytes, a group of fungi that cause skin infections known as tinea or ringworm in humans and animals. The medium contains ingredients that inhibit the growth of non-dermatophytic fungi and bacteria, while promoting the growth of dermatophytes. This allows for the easy identification and diagnosis of dermatophyte infections.

Composition

Dermatophyte Test Medium comprises several key components:

• Antibiotics (usually Cycloheximide and Chloramphenicol) to suppress the growth of saprophytic fungi and bacteria.
• Phenol red as a pH indicator, which changes color in the presence of dermatophytes due to the alkaline byproducts they produce.
• Nutrients to support the growth of dermatophytes, including sources of Carbon and Nitrogen.

Mechanism

The principle behind DTM's functionality lies in its selective inhibition and the pH indicator. Dermatophytes metabolize the nutrients in the medium, producing alkaline byproducts that cause the phenol red in the medium to shift from yellow to red. This color change is a positive indication of the presence of dermatophytes. Non-dermatophytic organisms, if they grow at all, do not produce a significant change in the medium's color.

Usage

DTM is widely used in veterinary and medical laboratories for the presumptive identification of dermatophyte infections. A sample from the infected area is placed on the medium and incubated at room temperature. A color change to red within a specified period, typically 14 days, suggests a positive result for dermatophytes. However, a definitive diagnosis may require further microscopic examination and culture identification.

Advantages and Limitations

The primary advantage of DTM is its ability to quickly and easily screen for dermatophyte infections. However, it is not without limitations. False positives can occur, and the medium does not differentiate between different species of dermatophytes. Additionally, some dermatophyte species may be inhibited by the antibiotics present in the medium.

Conclusion

Dermatophyte Test Medium is a valuable tool in the diagnosis of dermatophyte infections. Its selective properties allow for the efficient identification of these fungi, facilitating timely and appropriate treatment. However, it should be used in conjunction with other diagnostic methods to ensure accuracy.