Survival of Dermatophytes in Skin Scales after 10 Years Storage

Background: Survival of dermatophytes in skin scales and nail scraps sampled from human lesions could have ecological and epidemiological importance. The aim of this study was to store human skin scale and nail lesions infected with dermatophyte agents, at -20°C for a long time and to investigate the re-isolation rate of dermatophytes species from such samples after storage. Materials and Methods: After referral to Medical Mycology Laboratory of Tehran University of Medical Science, the patients were subjected to sampling. Confirmation of dermatophyte positive result in direct smears was done with Potassium hydroxide, then culturing on Sabouraud dextrose agar media was performed, and species were identified using standard procedures, and remaining samples were stored at -20°C. After 10 years, samples were re-examined for the presence and re-isolation of intended fungi according to the standard procedures. Results: From a total of 5 species enrolled in this study, Epidermophyton floccosum, Trichophyton mentagrophytes, and Tricholosporum violaceum survived, and Trichophyton rubrum and Trichophyton verrucosum lost their viability at -20°C after 10 years. There was a significant difference between the re-isolation rate and the type of dermatophytes (p<.05). E. floccosum had the highest re-isolation rate (66.7%), followed by T. mentagrophytes (27%). All of the re-isolated dermatophytes were taken from scales samples, but none from nail scraps samples. Conclusion: Some dermatophytes species including E. floccosum are able to maintain their ability to survive for a long time in human scale samples in certain time and temperature conditions (10 years at -20 °C) and to grow in appropriate conditions. These findings should be considered in ecological and epidemiological studies.