ABSTRACT
BACKGROUND: Onychomycosis affects up to 50% of patients in the older population. OBJECTIVES: This study aimed to explore heat sensitivity of Trichophyton rubrum and Trichophyton interdigitale as pathogens of onychomycosis. MATERIALS & METHODS: 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 ï¢-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. RESULTS: 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 ï¢-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. CONCLUSION: The heat resistance of T. rubrum and interdigitale should be considered using non-medical thermal treatment.
Subject(s)
Onychomycosis , Humans , Trichophyton , Ciclopirox/pharmacology , Hot Temperature , PowdersABSTRACT
Chronic recalcitrant dermatophytoses, due to Trichophyton (T.) mentagrophytes Type VIII are on the rise in India and are noteworthy for their predominance. It would not be wrong to assume that travel and migration would be responsible for the spread of T. mentagrophytes Type VIII from India, with many strains resistant to terbinafine, to other parts of the world. From September 2016 until March 2020, a total of 29 strains of T. mentagrophytes Type VIII (India) were isolated. All patients were residents of Germany: 12 females, 15 males and the gender of the remaining two was not assignable. Patients originated from India (11), Pakistan (two), Bangladesh (one), Iraq (two), Bahrain (one), Libya (one) and other unspecified countries (10). At least two patients were German-born residents. Most samples (21) were collected in 2019 and 2020. All 29 T. mentagrophytes isolates were sequenced (internal transcribed spacer (ITS) and translation elongation factor 1-α gene (TEF1-α)). All were identified as genotype VIII (India) of T. mentagrophytes. In vitro resistance testing revealed 13/29 strains (45%) to be terbinafine-resistant with minimum inhibitory concentration (MIC) breakpoints ≥0.2 µg/mL. The remaining 16 strains (55%) were terbinafine-sensitive. Point mutation analysis revealed that 10/13 resistant strains exhibited Phe397Leu amino acid substitution of squalene epoxidase (SQLE), indicative for in vitro resistance to terbinafine. Two resistant strains showed combined Phe397Leu and Ala448Thr amino acid substitutions, and one strain a single Leu393Phe amino acid substitution. Out of 16 terbinafine-sensitive strains, in eight Ala448Thr, and in one Ala448Thr +, new Val444 Ile amino acid substitutions were detected. Resistance to both itraconazole and voriconazole was observed in three out of 13 analyzed strains. Treatment included topical ciclopirox olamine plus topical miconazole or sertaconazole. Oral itraconazole 200 mg twice daily for four to eight weeks was found to be adequate. Terbinafine-resistant T. mentagrophytes Type VIII are being increasingly isolated. In Germany, transmission of T. mentagrophytes Type VIII from the Indian subcontinent to Europe should be viewed as a significant public health issue.
