Terbinafine‐resistant strain of Trichophyton interdigitale strain isolated from a tinea pedis patient

Abstract

Trichophyton interdigitale is an anthropophilic species that is frequently isolated from tinea unguium and tinea pedis throughout the world. In the present study, antifungal susceptibility testing was performed on T. interdigitale isolates from Japanese patients (isolated in 2017–2018; 24 strains) to assess itraconazole (ITZ) and terbinafine (TRF) susceptibility of these strains. E‐test determinations revealed that the mean ITZ minimum inhibitory concentration (MIC) of the 24 strains was 0.023 mg/L (range, 0.064–1). Clinical Laboratory Standards Institute M38‐A2 determinations revealed that the mean TRF MIC of 23 of the 24 strains was less than 0.03125 mg/L. Among these strains, one (NUBS18016) had a TRF MIC of 2 mg/L, confirming its resistance to TRF. The predicted amino acid sequences of the squalene epoxidase (SQLE) gene from the TRF‐resistant strain (NUBS18016) was 100% identical to the SQLE gene sequence of the reference strain T. interdigitale, indicating that no gene mutations were present in NUBS18016. Therefore, the TRF‐resistance mechanism of our TRF‐resistant strain NUBS18016 has not been defined. Dermatologists should be cautious about the prevalence of foot dermatophytosis due to antifungal drug‐resistant strains.

<p>Emergence of Terbinafine Resistant <em>Trichophyton mentagrophytes</em> in Iran, Harboring Mutations in the Squalene Epoxidase (<em>SQLE</em>) Gene</p>

“…19 The TRB MIC values in resistant TMTISG isolates from Iran and other countries varied in the range ≥1-≥32 μg/mL. [12][13][14][16][17][18] In the current report, similar to some other studies, 5,15,17,19 all TRB resistant isolates belonged to T. mentagrophytes species and ITS type VIII (5/28; 18%). Despite this, careful analysis of the literature revealed resistant Type II strains (Table 3).…”

“…To the extent of our knowledge, TRB resistance in TMTISG isolates has already been reported from at least eight Asian and European countries, including India, 5,12,14,15 Switzerland, 11,16 Japan, 13 Finland, 17 Denmark, 18 Bahrain, 19 Russia, 32 and Germany. 19 The TRB MIC values in resistant TMTISG isolates from Iran and other countries varied in the range ≥1-≥32 μg/mL.…”

“…In some cases, in vitro resistance could not be explained by the presence of any mutation in SQLE (wild type). 12,13 Then, mechanisms other than Phe397Leu and Leu393Phe substitution should still be considered as alternatives for TRB treatment failure. For example, Santos et al, recently showed that TRB resistance in T. rubrum can be mediated by multiplication of salicylate 1-monooxygenase (salA) gene.…”

“…9,10 Nonetheless, recent reports from India and some other Asian and European countries indicate that clinical/microbial TRB resistance now involves T. interdigitale and T. mentagrophytes. 5,[11][12][13][14][15][16][17][18][19] Since these fungi are essentially conspecific, 20 they can be treated together as the T. mentagrophytes/T. interdigitale species group (TMTISG).…”

In Vitro Ravuconazole Susceptibility of Anthropophilic Dermatophyte Strains Isolated from Japanese Patients

“…In a previous report, we also described the ITCZ low susceptible strain (MIC: 1 mg/L) and TEBF resistant strain (MIC: 2 mg/L) of T. interdigitale from Japanese patients (4). We expect that high-level tolerance or resistance to azoles and/or other antifungal drugs will develop in dermatophytes in Japan.…”