Increasing and Alarming Prevalence of Trichophyton indotineae as the Primary Causal Agent of Skin Dermatophytosis in Iran.

Background: Trichophyton indotineae, formerly described as T. mentagrophytes rDNA-ITS genotype VIII, has recently been identified as a novel species within the T. mentagrophytes complex. It has rapidly replaced T. rubrum as the predominant dermatophyte. In this study, skin dermatophyte isolates collected from patients in Iran were sequence-analysed for species identification. Additionally, the current prevalence of T. indotineae was compared with data from the previous decade.

Methods: A total of 194 dermatophyte isolates were collected from patients in four cities across Iran between July and December 2023, with 73 isolates of the T. mentagrophytes complex from the past decade also included. DNA was extracted from fresh colonies, and the internal transcribed spacer (ITS) 1-5.8S rDNA-ITS2 region was PCR-amplified and sequenced, followed by bioinformatic sequence analysis.

Results: Out of the 194 dermatophyte isolates, 132 samples (68.04%) were identified as T. indotineae, followed by T. tonsurans (14.43%), T. rubrum (7.22%), Microsporum canis (4.64%), T. interdigitale (3.61%), T. mentagrophytes (1.55%) and Arthroderma benhamiae (0.51%). Sequence analysis of 73 isolates from the past decade showed T. indotineae as the most frequently identified species (43.83%), followed by T. interdigitale (32.88%), T. mentagrophytes (21.92%) and Nannizzia fulva (1.37%). These findings indicate an increasing prevalence of T. indotineae in Iran in recent years. We analysed 214 T. mentagrophytes/T. interdigitale isolates, identifying 164 as T. indotineae, including 26 with nucleotide variations. A phylogenetic tree highlighted the genetic diversity within the species complex.

Conclusion: The alarmingly high prevalence of the potentially drug-resistant species T. indotineae signals the necessity of continuous surveillance of skin dermatophytosis in the community.