Caution and warning: Arrival of terbinafine‐resistant Trichophyton interdigitale of the Indian genotype, isolated from extensive dermatophytosis, in Japan

Clinico-mycological and therapeutic updates on cutaneous dermatophytic infections in the era of Trichophyton indotineae

Trichophyton indotineae has emerged as a novel dermatophyte species resulting in treatment recalcitrant skin infections. While the earliest reports came from India, T. indotineae has now spread to many parts of the world and is rapidly becoming a global health concern. Accurate identification of T. indotineae requires elaborate mycological investigations which is beyond the domain of routine microbiology testing. Extensive, non-inflammatory and atypical presentations are commonly seen with this novel species. T. indotineae shows an alarmingly high rate of mutations in the squalene epoxidase gene leading to lowered in vitro susceptibility to terbinafine. This has also translated into a lowered clinical response and requirement of a higher dose and much longer durations of treatment with the drug. Although the species remains largely susceptible to itraconazole, prolonged treatment durations are required to achieve cure with itraconazole. Fluconazole and griseofulvin do not have satisfactory in vitro or clinical activity. Apart from requirement of prolonged treatment durations, relapse postsuccessful treatment is a distressing and yet unexplained consequence of this "species-shift." Use of third generation azoles and combinations of systemic antifungals is unwarranted as both have not demonstrated clear superiority over itraconazole given alone, and the former is an important class of drugs for invasive mycoses.

Terbinafine-resistant T. indotineae due to F397L/L393S or F397L/L393F mutation among corticoid-related tinea incognita patients

Tinea incognita (TI) can mimic other dermatoses, presenting a diagnostic challenge for dermatologists. In some uncertain cases, it is crucial to accurately identify the causative agent using internal transcribed spacer (ITS) sequencing. The global issue of drug-resistant dermatophytosis is increasing, with Trichophyton (T.) indotineae being the main cause. This study presents four cases of TI (diagnosed as eczema) by terbinafine-resistant T. indotineae strains and reviews the current global TI epidemiology based on geographical continent and related conditions. Furthermore, squalene epoxidase (SQLE)-associated resistance mechanisms are evaluated. Lesions caused by terbinafine-resistant T. indotineae strains do not respond to allylamine antifungals, thus allowing the infection to spread. Among T. indotineae isolates, the SQLE F397L substitution is the most prevalent mutation contributing to azole resistance. F397L and L393F replacements in SQLE were detected in all isolates that exhibited high-level resistance. L393S was seen in isolates with low-resistant strains. Interestingly, and for the first time, an L393F amino acid substitution in the SQLE gene product was detected in the Iranian clinical T. indotineae strain. Also, a genomics-based update on terbinafine resistance that focuses on T. indotineae is discussed in this study.

Terbinafine resistance in Trichophyton mentagrophytes and Trichophyton rubrum in the Czech Republic: A prospective multicentric study

BACKGROUND

Terbinafine, an allylamine antifungal, is crucial for treating dermatophytosis by inhibiting squalene epoxidase (SQLE) in the ergosterol biosynthetic pathway. However, resistance is emerging, particularly in India and Southeast Asia, but reports of resistance spread worldwide. Despite this, comprehensive studies on terbinafine resistance in Trichophyton are still limited.

OBJECTIVES

This research aimed to determine the prevalence of terbinafine resistance in the Czech Republic, with a focus on Trichophyton rubrum and Trichophyton mentagrophytes, and investigate the underlying molecular mechanisms.

PATIENTS/METHODS

A total of 514 clinical strains of T. rubrum and 240 T. mentagrophytes collected from four Czech clinical institutions were screened for terbinafine resistance. Molecular investigations included DNA sequencing, specifically the ITS rDNA region and SQLE gene, as well as antifungal susceptibility testing following EUCAST guidelines.

RESULTS

While no resistance was observed in T. rubrum, 2.5% of T. mentagrophytes strains exhibited resistance, marked by the F397L mutation in SQLE. Notably, resistance surged from 1.2% in 2019 to 9.3% in 2020 but reverted to 0% in 2021. All resistant strains were identified as T. mentagrophytes var. indotineae. Resistant strains exhibited high MICs for terbinafine (≥4 mg L-1 ) but low MICs to the other seven antifungals tested except for fluconazole.

CONCLUSIONS

This study highlights the emergence of terbinafine-resistant T. mentagrophytes strains in the Czech Republic, with the F397L mutation being pivotal. Due to the relatively low resistance level, the current guidelines for dermatomycosis treatment in the Czech Republic remain effective, but ongoing surveillance is essential for timely adaptations if resistance patterns change.

Combatting antifungal resistance: Paradigm shift in the diagnosis and management of onychomycosis and dermatomycosis

Antifungal resistance has become prevalent worldwide. Understanding the factors involved in spread of resistance allows the formulation of strategies to slow resistance development and likewise identify solutions for the treatment of highly recalcitrant fungal infections. To investigate the recent explosion of resistant strains, a literature review was performed focusing on four main areas: mechanisms of resistance to antifungal agents, diagnosis of superficial fungal infections, management, and stewardship. The use of traditional diagnostic tools such as culture, KOH analysis and minimum inhibitory concentration values on treatment were investigated and compared to the newer techniques such as molecular methods including whole genome sequencing, and polymerase chain reaction. The management of terbinafine-resistant strains is discussed. We have emphasized the need for antifungal stewardship including increasing surveillance for resistant infection.

The emergence of Trichophyton indotineae: Implications for clinical practice

Emergence and increase of terbinafine-resistant dermatophytosis led to the identification of Trichophyton mentagrophytes internal transcriber space (ITS) genotype VIII in 2017, later renamed as Trichophyton indotineae and classified as a separate species in 2020. With its suspected origin in South Asia, this novel strain has emerged in Bahrain, Canada, Denmark, Finland, France, Germany, India, Iran, Japan, Russia, and Switzerland, with its spread attributed primarily to travel and migration. Diagnosis using routine mycology laboratory techniques is unable to distinguish T. indotineae from T. mentagrophytes and T. interdigitale; specific identification requires genomic sequencing to identify unique, specific markers. One speculated reason for this recent outbreak is the unrestricted use of topical steroid creams and antifungal agents. Patients with extensive tinea corporis and cruris due to T. indotineae present with inflammatory red plaques in multiple body sites. The majority of these infections prove to be resistant to conventional antifungals, including allylamines and azoles (itraconazole and fluconazole), thus emphasizing the need for antifungal susceptibility testing before treatment initiation and for reassessing in nonresponsive patients. Molecular studies have identified several point mutations in the ERG1 (terbinafine resistance) and ERG11 (azole resistance) genes, which need to be analyzed further. Use of relatively new agents, such as voriconazole and luliconazole, as well as device modalities and combination therapy, could be investigated for recalcitrant T. indotineae infections.

Tinea Gladiatorum: Epidemiology, Clinical Aspects, and Management

Tinea gladiatorum (TG) is a fungal skin infection that occurs among wrestlers and other contact sport athletes with a varied prevalence rate. The most common causative factor responsible as well for local outbreaks of the infection is an anthropophilic dermatophyte species—Trichophyton tonsurans (T. tonsurans). The purpose of this study was to gather current data about TG, including epidemiology, possible diagnosing methods, clinical features, treatment approaches, and potential prevention techniques. We also performed a systematic review of studies describing TG incidence. The prevalence of the disease varied from 2.4% up to 100%. That wide range of variability forces medical practitioners to update knowledge about TG and points to the fact that it still may be a diagnostic and therapeutic challenge. Spreading awareness among athletes and trainers is one of the most important preventive steps.

The epidemic of the multiresistant dermatophyte Trichophyton indotineae has reached China

Due to its high degree of natural resistance to terbinafine in vitro and its tendency to spread globally from the Indian subcontinent, the emerging dermatophyte Trichophyton indotineae has become a major concern in dermatology. Herein, we present the first report of T. indotineae from mainland China. The transmission of the fungus to Guizhou Province in central China and eventual host susceptibilities were investigated. We studied 31 strains of the T. mentagrophytes complex from outpatient clinics of our hospital collected during the past 5 years. The set comprised four ITS genotypes, two of which were T. mentagrophytes genotype VIII, now known as Trichophyton indotineae; the earliest isolation in the Guiyang area appeared to date back to 2018. The isolate was derived from an Indian patient, while local Chinese patients had no dermatophytosis caused by this genotype. Reports from around the world indicated that almost all of the globally reported T. indotineae cases originated from the Indian subcontinent and surrounding countries without transmission among native populations, suggesting deviating local conditions or racial differences in immunity against this fungus.

Antifungal Resistance in Dermatophytes: Genetic Considerations, Clinical Presentations and Alternative Therapies

Numerous reports describe the emergence of resistance in dermatophytes, especially in T. rubrum and T. mentagrophytes/indotineae strains. We here present a review of the current status of resistance in dermatophytes worldwide. Resistance to terbinafine is mainly discussed, with different mutations found in the squalene epoxidase gene also considered. Resistance to azoles is also approached. Clinical presentations caused by resistant dermatophytes are presented, together with alternative therapies that help to better manage these kind of infections.

Antifungal Combinations in Dermatophytes

Dermatophytes are the most common cause of fungal infections worldwide, affecting millions of people annually. The emergence of resistance among dermatophytes along with the availability of antifungal susceptibility procedures suitable for testing antifungal agents against this group of fungi make the combinatorial approach particularly interesting to be investigated. Therefore, we reviewed the scientific literature concerning the antifungal combinations against dermatophytes. A literature search on the subject performed in PubMed yielded 68 publications: 37 articles referring to in vitro studies and 31 articles referring to case reports or clinical studies. In vitro studies involved over 400 clinical isolates of dermatophytes (69% Trichophyton spp., 29% Microsporum spp., and 2% Epidermophyton floccosum). Combinations included two antifungal agents or an antifungal agent plus another chemical compound including plant extracts or essential oils, calcineurin inhibitors, peptides, disinfectant agents, and others. In general, drug combinations yielded variable results spanning from synergism to indifference. Antagonism was rarely seen. In over 700 patients with documented dermatophyte infections, an antifungal combination approach could be evaluated. The most frequent combination included a systemic antifungal agent administered orally (i.e., terbinafine, griseofulvin, or azole-mainly itraconazole) plus a topical medication (i.e., azole, terbinafine, ciclopirox, amorolfine) for several weeks. Clinical results indicate that association of antifungal agents is effective, and it might be useful to accelerate the clinical and microbiological healing of a superficial infection. Antifungal combinations in dermatophytes have gained considerable scientific interest over the years and, in consideration of the interesting results available so far, it is desirable to continue the research in this field.

ATP-binding Cassette (ABC) Transporter Proteins in Highly Terbinafine-resistant Strains of Trichophyton indotineae (Former Species Name: Trichophyton interdigitale)

To clarify the terbinafine (TRF) resistance mechanism in highly TRF-resistant [minimum inhibitory concentration (MIC) >32 μg/mL] strains of Trichophyton indotineae (NUBS19006^T and NUBS19007), we investigated the expression of squalene epoxidase (SQLE), pleiotropic drug resistance 1 (PDR1), multidrug resistance 2 (MDR2), and MDR4 genes by real-time quantitative PCR analysis, given the known interaction of the corresponding proteins with antifungals and the efflux blocker tacrolimus (FK506). SQLE, PDR1, MDR2, and MDR4 transcript levels in TRF-resistant strains cultured in SDB were not significantly higher than those of the respective genes in TRF-susceptible strains (1 and 10). By contrast, PDR1, MDR2, and MDR4 transcript levels in TRF-resistant and TRF-susceptible strains cultured in SDB containing 10 μg/mL TRF were 5-100 times higher than those of the respective genes in strains grown in the absence of TRF. However, no differences in PDR1, MDR2, and MDR4 transcript levels were found between TRF-resistant (NUBS19006^T and NUBS19007) and TRF-susceptible strains cultured in SDB containing 10 μg/mL TRF. The interaction between TRF and FK506 on antifungal activity was not detected in TRF-resistant strains. These results indicate that ATP-dependent efflux pumps do not confer TRF-resistance mechanisms in TRF-resistant strains.

Molecular Epidemiology and Antifungal Susceptibility of Trichophyton Isolates in Greece: Emergence of Terbinafine-Resistant Trichophytonmentagrophytes Type VIII Locally and Globally

Trichophyton isolates with reduced susceptibility to antifungals are now increasingly reported worldwide. We therefore studied the molecular epidemiology and the in vitro antifungal susceptibility patterns of Greek Trichophyton isolates over the last 10 years with the newly released EUCAST reference method for dermatophytes. Literature was reviewed to assess the global burden of antifungal resistance in Trichophyton spp. The in vitro susceptibility of 112 Trichophyton spp. molecularly identified clinical isolates (70 T. rubrum, 24 T. mentagrophytes, 12 T. interdigitale and 6 T. tonsurans) was tested against terbinafine, itraconazole, voriconazole and amorolfine (EUCAST E.DEF 11.0). Isolates were genotyped based on the internal transcribed spacer (ITS) sequences and the target gene squalene epoxidase (SQLE) was sequenced for isolates with reduced susceptibility to terbinafine. All T. rubrum, T. interdigitale and T. tonsurans isolates were classified as wild-type (WT) to all antifungals, whereas 9/24 (37.5%) T. mentagrophytes strains displayed elevated terbinafine MICs (0.25–8 mg/L) but not to azoles and amorolfine. All T. interdigitale isolates belonged to ITS Type II, while T. mentagrophytes isolates belonged to ITS Type III* (n = 11), VIII (n = 9) and VII (n = 4). All non-WT T. mentagrophytes isolates belonged to Indian Genotype VIII and harbored Leu393Ser (n = 5) and Phe397Leu (n = 4) SQLE mutations. Terbinafine resistance rates ranged globally from 0–44% for T. rubrum and 0–76% for T. interdigitale/T. mentagrophytes with strong endemicity. High incidence (37.5%) of terbinafine non-WT T. mentagrophytes isolates (all belonging to ITS Type VIII) without cross-resistance to other antifungals was found for the first time in Greece. This finding must alarm for susceptibility testing of dermatophytes at a local scale particularly in non-responding dermatophytoses.

A Case of Tinea Faciei, Tinea Corporis, and Tinea Unguium with Dermatophytoma Successfully Treated with Oral Fosravuconazole L-lysine Ethanolate

We present a 76-year-old Japanese male with tinea faciei, tinea corporis, and tinea unguium with dermatophytoma. We performed fungal culture and confirmed the causative fungus to be Trichophyton rubrum. We treated the patient using oral fosravuconazole l-lysine ethanolate (F-RVCZ). More than one year has passed since the end of treatment, but there has been no recurrence. This case suggests that F-RVCZ is effective for tinea other than tinea unguium.

Epidemiological study of terbinafine-resistant dermatophytes isolated from Japanese patients

Terbinafine (TRF) has been used in the treatment of fungal infections for more than 20 years. Recently, TRF-resistant Trichophyton interdigitale and T. rubrum strains have been isolated from human patients worldwide. However, an epidemiological study of TRF-resistant strains in Japanese patients has not been investigated. In the present study, antifungal susceptibility testing was performed on clinical isolates from Japanese patients to assess TRF-resistance patterns of T. interdigitale and T. rubrum strains. We also sequenced the squalene epoxidase (SQLE) encoding gene of TRF-resistant T. rubrum strains. Two hundred and ten T. interdigitale and T. rubrum clinical isolates were obtained from 210 human cases of tinea pedis, tinea corporis, tinea unguium, tinea cruris, tinea manuum, tinea faciei and tinea capitis in Tokyo, Saitama, Chiba, Hyogo and Kumamoto, Japan, in 2020. Five T. rubrum isolates (N74, N79, N99, H30 and K2) grew on Sabouraud's dextrose agar (SDA) containing 1 mg/L of TRF. All five strains exhibited TRF minimum inhibitory concentrations (MICs) ≥32 mg/L but remained susceptible to azoles. We determined SQLE sequences in these TRF-resistant T. rubrum strains and found that all strains harbored missense mutations (L393F) in the SQLE-encoding gene.

Trichophyton indotineae sp. nov.: A New Highly Terbinafine-Resistant Anthropophilic Dermatophyte Species

In this report, we describe the first isolation of two highly terbinafine (TRF)-resistant Trichophyton interdigitale-like strains from a Nepali patient and an Indian patient with tinea corporis in Japan. These strains (designated NUBS19006 and NUBS19007) exhibited a TRF minimal inhibitory concentration (MIC) of > 32 mg/L and contained a missense mutation (Phe397Leu) in squalene epoxidase (SQLE) gene. The internal transcribed spacer (ITS) region sequences amplified from the isolates (NUBS19006 and NUBS19007) were 99.5% identical to Japanese isolates of T. interdigitale and T. interdigitale strain CBS 428.63. The homology of region sequences were also 97.6% identical to T. mentagrophytes strain CBS 318.56. Moreover, the ITS sequences amplified from the isolates were 100% identical to highly TRF-resistant strains of T. interdigitale, which were isolated in Delhi, India, and harbored mutations in SQLE. The urease test on Christensen's urease agar was positive for T. mentagrophytes and T. interdigitale after 7 days of incubation. On the other hand, the type strain of T. rubrum CBS 100081 ^T and highly TRF-resistant strains (NUBS19006 and NUBS19007) were negative on Christensen urease agar after 7 and 14 days of incubation. Moreover, NUBS19006 and NUBS19007 were also negative reaction on the hair perforation test. To avoid confusion in the taxonomy of the T. mentagrophytes/T. interdigitale complex, we suggest that the highly TRF-resistant Indian strains be considered a new species independent of T. interdigitale, according to clinical and mycological features.

Alarming India-wide phenomenon of antifungal resistance in dermatophytes: A multicentre study

BACKGROUND

An alarming increase in recalcitrant dermatophytosis has been witnessed in India over the past decade. Drug resistance may play a major role in this scenario.

OBJECTIVES

The aim of the present study was to determine the prevalence of in vitro resistance to terbinafine, itraconazole and voriconazole in dermatophytes, and to identify underlying mutations in the fungal squalene epoxidase (SQLE) gene.

PATIENTS/METHODS

We analysed skin samples from 402 patients originating from eight locations in India. Fungi were identified by microbiological and molecular methods, tested for antifungal susceptibility (terbinafine, itraconazole, voriconazole), and investigated for missense mutations in SQLE.

RESULTS

Trichophyton (T.) mentagrophytes internal transcribed spacer (ITS) Type VIII was found in 314 (78%) samples. Eighteen (5%) samples harboured species identified up to the T interdigitale/mentagrophytes complex, and T rubrum was detected in 19 (5%) samples. 71% of isolates were resistant to terbinafine. The amino acid substitution Phe397Leu in the squalene epoxidase of resistant T mentagrophytes was highly prevalent (91%). Two novel substitutions in resistant Trichophyton strains, Ser395Pro and Ser443Pro, were discovered. The substitution Ala448Thr was found in terbinafine-sensitive and terbinafine-resistant isolates but was associated with increased MICs of itraconazole and voriconazole.

CONCLUSIONS

The high frequencies of terbinafine resistance in dermatophytes are worrisome and demand monitoring and further research. Squalene epoxidase substitutions between Leu393 and Ser443 could serve as markers of resistance in the future.