Evaluation of the heat sensitivity of Trichophyton rubrum and Trichophyton interdigitale

Onychomycosis affects up to 50% of patients in the older population.

This study aimed to explore heat sensitivity of Trichophyton rubrum and Trichophyton interdigitale as pathogens of onychomycosis.

The fungi were heated in sterile saline solution up to 100°C for five or 10 minutes with or without additional previous treatment with 1% ciclopirox solution or chitinase and 1,3 -galactidase or for 45 minutes at 40°C or 60°C with washing powder. Subsequently, the fungi were cultured and regrowth was assessed after one week.

After heating T. rubrum for five minutes at 60°C, growth was completely inhibited. After heating T. interdigitale for five minutes at 60°C, all of the samples regrew, and at 95°C, none of the samples regrew. No difference between five and 10-minute heating was observed. Previous incubation with 1% ciclopirox solution for 24 hours inhibited the growth of T. rubrum completely. T. interdigitale was still able to regrow to 100% after five minutes at 40°C, to 33% after 60°C, and to 22% after 80°C. Incubation for 45 minutes with washing powder solution at 40°C or 60°C did not lead to significant growth reduction of T. rubrum or interdigitale. Two hours incubation with -1,3-glucanase and chitinase prior to five minutes of heating to 60°C and 80°C reduced the heat resistance of T. interdigitale; growth was inhibited in 56% and 100% of the samples, respectively.

The heat resistance of T. rubrum and interdigitale should be considered using non-medical thermal treatment.