"Indian" strains of Trichophyton mentagrophytes with reduced itraconazole susceptibility in Germany

Antifungal resistance in dermatophytes - review of the epidemiology, diagnostic challenges and treatment strategies for managing Trichophyton indotineae infections

INTRODUCTION

There is an increasing number of reports of Trichophyton indotineae infections. This species is usually poorly responsive to terbinafine.

AREAS COVERED

A literature search was conducted in May 2024. T.indotineae infections detected outside the Indian subcontinent are generally associated with international travel. Reports of local spread are mounting.As a newly identified dermatophyte species closely related to the T. mentagrophytes complex with limited genetic and phenotypic differences, there is an unmet need to develop molecular diagnosis for T. indotineae. Terbinafine has become less effective as a first-line agent attributed to mutations in the squalene epoxidase gene (Leu393Phe, Phe397Leu). Alternative therapies include itraconazole for a longer time-period or a higher dose (200 mg/day or higher). Generally, fluconazole and griseofulvin are not effective. In some cases, especially when the area of involvement is relatively small, topical non-allylamine antifungals may be an option either as monotherapy or in combination with oral therapy. In instances when the patient relapses after apparent clinical cure then itraconazole may be considered. Good antifungal stewardship should be considered at all times.

EXPERT OPINION

When both terbinafine and itraconazole are ineffective, options include off-label triazoles (voriconazole and posaconazole). We present four patients responding to these newer triazoles.

Dermatophyte infection: from fungal pathogenicity to host immune responses

Dermatophytosis is a common superficial infection caused by dermatophytes, a group of pathogenic keratinophilic fungi. Apart from invasion against skin barrier, host immune responses to dermatophytes could also lead to pathologic inflammation and tissue damage to some extent. Therefore, it is of great help to understand the pathogenesis of dermatophytes, including fungal virulence factors and anti-pathogen immune responses. This review aims to summarize the recent advances in host-fungal interactions, focusing on the mechanisms of anti-fungal immunity and the relationship between immune deficiency and chronic dermatophytosis, in order to facilitate novel diagnostic and therapeutic approaches to improve the outcomes of these patients.

Antifungal Resistance, Susceptibility Testing and Treatment of Recalcitrant Dermatophytosis Caused by Trichophyton indotineae: A North American Perspective on Management

There is an ongoing epidemic of chronic, relapsing dermatophytoses caused by Trichophyton indotineae that are unresponsive to one or multiple antifungal agents. Although this new species may have originated from the Indian subcontinent, there has been a notable increase of its reporting in other countries. Based on current literature, antifungal susceptibility testing (AFST) showed a large variation of terbinafine minimum inhibitory concentrations (MICs) (0.04 to ≥ 32 µg/ml). Elevated terbinafine MICs can be attributed to mutations in the squalene epoxidase gene (single mutations: Leu393Phe, Leu393Ser, Phe397Leu, and double mutations: Leu393Phe/Ala448Thr, Phe397Leu/Ala448Thr). Itraconazole MICs had a lower range when compared with that of terbinafine (0.008-16 µg/ml, with most MICs falling between 0.008 µg/ml and < 1 µg/ml). The interpretation of AFST results remains challenging due to protocol variations and a lack of established breakpoints. Adoption of molecular methods for resistance detection, coupled with AFST, may provide a better evaluation of the in vitro resistance status of T. indotineae. There is limited information on treatment options for patients with confirmed T. indotineae infections by molecular diagnosis; preliminary evidence generated from case reports and case series points to itraconazole as an effective treatment modality, while terbinafine and griseofulvin are generally not effective. For physicians working outside of endemic regions, there is currently an unmet need for standardized clinical trials to establish treatment guidelines; in particular, combination therapy of oral and topical agents (e.g., itraconazole and ciclopirox), as well as with other azoles (i.e., fluconazole, voriconazole, ketoconazole), warrants further investigation as multidrug resistance is a possibility for T. indotineae.

The Domestic Isolation of Terbinafine- and Itraconazole-Resistant Trichophyton indotineae in Chinese Mainland

BACKGROUND

Trichophyton indotineae, a new species of dermatophytes, has become a significant concern in treating dermatophytosis due to the high level of terbinafine resistance reported in India and even worldwide.

OBJECTIVES

This study aimed to report the terbinafine- and itraconazole-resistant T. indotineae in Chinese mainland, by identifying the phylogenetic classification of the isolate strain, and detecting the drug resistance, gene mutation and expression.

PATIENTS/METHODS

The skin scales of the patient were cultured on SDA and the isolate was authenticated by DNA sequencing and MALDI-TOF MS. Antifungal susceptibility testing was performed following the M38-A2 CLSI protocol to examine the MICs values of terbinafine, itraconazole, fluconazole, etc. The strain was screened for mutations in the squalene epoxidase (SQLE) gene by Sanger sequencing and detected the expression of CYP51A and CYP51B by qRT-PCR.

RESULTS

A multi-resistant ITS genotype VIII sibling of the T. mentagrophytes complex (T. indotineae) was isolated in Chinese mainland. The strain harbored high terbinafine MIC of > 32 μg/mL and itraconazole MIC of 1.0 μg/mL, which was identified a mutation in the squalene epoxidase gene with amino acid substitution (Phe397Leu, mutation 1191C > A). In addition, overexpression of CYP51A and CYP51B was observed. With multiple relapses, the patient finally achieved clinical cure by itraconazole pulse therapy and topical clotrimazole cream for 5 weeks.

CONCLUSIONS

The first domestic strain of terbinafine- and itraconazole-resistant T. indotineae from a patient in Chinese mainland was isolated. Itraconazole pulse therapy can be an effective method for the treatment of T. indotineae.

Current Topics in Dermatophyte Classification and Clinical Diagnosis

Dermatophytes are highly infectious fungi that cause superficial infections in keratinized tissues in humans and animals. This group of fungi is defined by their ability to digest keratin and encompasses a wide range of species. Classification of many of these species has recently changed due to genetic analysis, potentially affecting clinical diagnosis and disease management. In this review, we discuss dermatophyte classification including name changes for medically important species, current and potential diagnostic techniques for detecting dermatophytes, and an in-depth review of Microsporum canis, a prevalent zoonotic dermatophyte. Fungal culture is still considered the “gold standard” for diagnosing dermatophytosis; however, modern molecular assays have overcome the main disadvantages of culture, allowing for tandem use with cultures. Further investigation into novel molecular assays for dermatophytosis is critical, especially for high-density populations where rapid diagnosis is essential for outbreak prevention. A frequently encountered dermatophyte in clinical settings is M. canis, which causes dermatophytosis in humans and cats. M. canis is adapting to its primary host (cats) as one of its mating types (MAT1-2) appears to be going extinct, leading to a loss of sexual reproduction. Investigating M. canis strains around the world can help elucidate the evolutionary trajectory of this fungi.

Trichophyton indotineae-An Emerging Pathogen Causing Recalcitrant Dermatophytoses in India and Worldwide-A Multidimensional Perspective

Trichophyton (T.) indotineae is a newly identified dermatophyte species that has been found in a near-epidemic form on the Indian subcontinent. There is evidence of its spread from the Indian subcontinent to a number of countries worldwide. The fungus is identical to genotype VIII within the T. mentagrophytes/T. interdigitale species complex, which was described in 2019 by sequencing the Internal Transcribed Spacer (ITS) region of ribosomal DNA of the dermatophyte. More than 10 ITS genotypes of T. interdigitale and T. mentagrophytes can now be identified. T. indotineae causes inflammatory and itchy, often widespread, dermatophytosis affecting the groins, gluteal region, trunk, and face. Patients of all ages and genders are affected. The new species has largely displaced other previously prevalent dermatophytes on the Indian subcontinent. T. indotineae has become a problematic dermatophyte due to its predominantly in vitro genetic resistance to terbinafine owing to point mutations of the squalene epoxidase gene. It also displays in vivo resistance to terbinafine. The most efficacious drug currently available for this terbinafine-resistant dermatophytoses, based on sound evidence, is itraconazole.