Increasing Terbinafine Resistance in Danish Trichophyton Isolates 2019–2020

In vitro activity of olorofim against 507 filamentous fungi including antifungal drug-resistant strains at a tertiary laboratory in Australia: 2020-2023

BACKGROUND

New antifungal agents are required to mitigate against azole-resistant Aspergillus and drug-resistant non-Aspergillus moulds. The novel orotomide, olorofim (F2G, Manchester, UK), has potent fungicidal activity against Aspergillus including azole-resistant Aspergillus fumigatus, Lomentospora prolificans and Scedosporium spp. Development of olorofim-specific clinical breakpoints/epidemiological cut-off values requires reliable MIC data.

OBJECTIVES

Determine the in vitro activity of olorofim compared with standard antifungals against mould pathogens at an Australian hospital.

MATERIALS AND METHODS

Olorofim MICs were determined for 507 clinical mould isolates using the CLSI M38-A3 standard. MICs of amphotericin B, anidulafungin, posaconazole, voriconazole and isavuconazole were obtained using Sensititre™ YeastOne YO10 and AUSNMRCI panels (Thermo-Fisher Scientific).

RESULTS

A. fumigatus sensu stricto was the commonest species (33.3%) followed by L. prolificans (18.3%), Scedosporium (11.4%) and Fusarium (6%) species. Olorofim modal MICs were ≤0.25 mg/L (MIC90 0.25 mg/L) for all Aspergillus except Aspergillus Section Usti (1 mg/L); MICs for nine azole-resistant/non-wild-type A. fumigatus ranged from 0.008 to 0.125 mg/L. The MIC90 of olorofim for L. prolificans was 0.5 mg/L, 0.25-0.5 mg/L for Scedosporium spp. and 8 mg/L for the F. solani complex but with modal MICs of 0.25 and 0.008 mg/L for F. oxysporum and F. proliferatum complexes, respectively. For Verruconis gallopava (n = 10), the olorofim MIC90 was 0.06 mg/L (voriconazole MIC90 2 mg/L, isavuconazole MICs of 4->8 mg/L). Olorofim had little activity against other dematiaceous moulds including Exophiala species.

CONCLUSIONS

Olorofim was highly active against Aspergillus spp. including azole-resistant A. fumigatus, L. prolificans, Scedosporium spp. and some Fusarium species with the new finding of potent activity against V. gallopava.

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.

Twenty Years in EUCAST Anti-Fungal Susceptibility Testing: Progress & Remaining Challenges

Since its inception in 2002, the EUCAST Antifungal Susceptibility Testing Subcommittee (AFST) has developed and refined susceptibility testing methods for yeast, moulds and dermatophytes, and established epidemiological cut-off values and breakpoints for antifungals. For yeast, three challenges have been addressed. Interpretation of trailing growth in fluconazole susceptibility testing, which has been proven without impact on efficacy if below the 50% endpoint. Variability in rezafungin MIC testing due to laboratory conditions, which has been solved by the addition of Tween 20 to the growth medium in E.Def 7.4. And third, interpretation of MICs for rare yeast with no breakpoints, where recommendations have been established for MIC-based clinical advice. For moulds, refinements include the validation of spectrophotometer reading for A. fumigatus to facilitate objective MIC determination, and for dermatophytes the establishment of a microdilution method with automated reading and a selective medium to minimise the risk of contaminations. Recent initiatives involve development and validation of agar-based screening assays for detection of potential azole and echinocandin resistance in A. fumigatus and Aspergillus species, respectively, and of terbinafine resistance in Trichophyton species. Moreover, the development of a EUCAST guidance document for molecular resistance testing represents an advancement, particularly for identifying target gene alterations associated with resistance. In summary, EUCAST AFST continues to play a pivotal role in standardizing AFST and facilitating accurate interpretation of susceptibility data for clinical decision-making. Adoption of EUCAST breakpoints for commercial test methods, however, requires thorough validation to ensure concordance with EUCAST reference testing species-specific MIC distributions.

Potential emergence of terbinafine resistance by squalene epoxidase gene mutations: An 18-month cohort study of onychomycosis patients in the United States

BACKGROUND

There is a concerning rise in antifungal-resistant dermatophytosis globally, with resistance to terbinafine conferred by point mutations in the squalene epoxidase (SQLE) gene.

OBJECTIVES

Report changes in the prevalence and profile of SQLE mutations in onychomycosis patients in the United States.

METHODS

A longitudinal cohort study of toenail samples was collected from suspected onychomycosis patients over an 18-month period from 2022 to 2023. Samples were submitted from across the United States and subjected to multiplex real-time polymerase chain reactions for dermatophyte detection, with further screening of SQLE mutations at four known hotspots (393Leu, 397Phe, 415Phe and 440His).

RESULTS

A total of 62,056 samples were submitted (mean age: 57.5 years; female: 60.4%). Dermatophytes were detected in 38.5% of samples, primarily Trichophyton rubrum complex (83.6%) and T. mentagrophytes complex (10.7%). A survey of SQLE mutations was carried out in 22,610 dermatophyte samples; there was a significant increase in the prevalence of SQLE mutations between the first quarter of 2022 and the second quarter of 2023 (29.0 to 61.9 per 1000 persons). The Phe397Leu substitution was the predominant mutation; Phe415Ser and His440Tyr have also emerged which were previously reported as minor mutations in skin samples. The temporal change in mutation rates can be primarily attributed to the Phe415Ser substitution. Samples from elderly patients (>70 years) are more likely to be infected with the T. mentagrophytes complex including strains harbouring the Phe415Ser substitution.

CONCLUSION

The prevalence of SQLE mutations among onychomycosis patients with Trichophyton infections may be underestimated. Older individuals may have a higher risk.

The Impact of the Fungal Priority Pathogens List on Medical Mycology: A Northern European Perspective

Fungal diseases represent a considerable global health concern, affecting >1 billion people annually. In response to this growing challenge, the World Health Organization introduced the pivotal fungal priority pathogens list (FPPL) in late 2022. The FPPL highlights the challenges in estimating the global burden of fungal diseases and antifungal resistance (AFR), as well as limited surveillance capabilities and lack of routine AFR testing. Furthermore, training programs should incorporate sufficient information on fungal diseases, necessitating global advocacy to educate health care professionals and scientists. Established international guidelines and the FPPL are vital in strengthening local guidance on tackling fungal diseases. Future iterations of the FPPL have the potential to refine the list further, addressing its limitations and advancing our collective ability to combat fungal diseases effectively. Napp Pharmaceuticals Limited (Mundipharma UK) organized a workshop with key experts from Northern Europe to discuss the impact of the FPPL on regional clinical practice.

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.

Trichophyton indotineae, an Emerging Drug-Resistant Dermatophyte: A Review of the Treatment Options

Background: Dermatophytosis is a prevalent superficial infection caused by filamentous fungi, primarily affecting the skin and/or its appendages. In recent years, there has been a notable increase in mycotic strains resistant to standard antifungal therapies, including Trichophyton indotineae, a dermatophyte of the Trichophyton mentagrophytes complex. This review aims to provide a comprehensive overview of the treatment options for T. indotineae, elucidating their effectiveness in managing this challenging mycotic infection. Methods: For this review, a search was conducted in the PubMed, Scopus, Web of Science, Embase, and Google Scholar databases, encompassing all published data until March 2024. English-language articles detailing therapy outcomes for patients confirmed to be affected by T. indotineae, identified through molecular analysis, were included. Results: Itraconazole was shown to be a good therapeutic choice, particularly when administered at a dosage of 200 mg/day for 1-12 weeks. Voriconazole was also demonstrated to be effective, while terbinafine exhibited a reduced response rate. Griseofulvin and fluconazole, on the other hand, were found to be ineffective. Although topical treatments were mostly ineffective when used alone, they showed promising results when used in combination with systemic therapy. Mutational status was associated with different profiles of treatment response, suggesting the need for a more tailored approach. Conclusions: When managing T. indotineae infections, it is necessary to optimize therapy to mitigate resistances and relapse. Combining in vitro antifungal susceptibility testing with mutational analysis could be a promising strategy in refining treatment selection.

Increased terbinafine resistance among clinical genotypes of Trichophyton mentagrophytes/T. interdigitale species complex harboring squalene epoxidase gene mutations

Terbinafine resistance has become epidemic as an emerging problem in treatment of dermatohpytosis. This could be attributed in part to a point mutation in the squalene epoxidase (SQLE) gene. In this study, point mutations in the SQLE gene were studied in T. rubrum and T. mentagrophytes/T. interdigitale species complex as two main causative agents of dermatophytosis. Antifungal susceptibility of clinical isolates of T. rubrum (n = 27) and T. mentagrophytes/T. interdigitale (n = 56) was assessed using the M38-3rd edition CLSI method. The SQLE gene and ITS region were sequenced for all the fungal strains, and the mutation sites and genotypes of the terbinafine-resistant strains were characterized. The results demonstrated that, in T. rubrum, the minimum inhibitory concentration of terbinafine (MIC50 and MIC90) was 0.03 μg/ml, and the geometric mean (G mean) concentration was 0.02. For the T. mentagrophytes complex, the MIC50 and MIC90 were 0.03 and 1.0 μg/ml, respectively, and the G mean concentration was 0.04 μg/ml. Four out of the five resistant strains were T. indotineae harboring the F397L and Q408L mutations, while the last one was T. mentagrophytes genotype VII, which harbors the F397L mutation. T. indotineae was the prominent causative agent of terbinafine resistance, with 80 % of the isolates, and T. mentagrophytes genotype VII was introduced as a new genotype in the terbinafine-resistant T. mentagrophytes complex. Our findings further substantiate the importance of antifungal susceptibility testing in selecting the choice of drug for effective treatment of dermatophytosis and highlight the importance of screening dermatophyte species for point mutations responsible for newly developed resistant strains to improve the current knowledge of overcoming infections caused by resistant species.

High Prevalence of Terbinafine Resistance Among Trichophyton mentagrophytes/T. interdigitale Species Complex, a Cross-Sectional Study from 2021 to 2022 in Northern Parts of Iran

Treatment-resistant dermatophytosis caused by the members of the Trichophyton mentagrophytes/Trichophyton interdigitale species group (TMTISG) is increasing worldwide. We aimed to determine the prevalence of TMTISG in patients with dermatophytosis in two centers from north of Iran and detect the possible mutations in the squalene epoxidase (SQLE) gene in relevant terbinafine (TRB) resistant pathogenic isolates. From November 2021 to December 2022, 1960 patients suspected to dermatophytosis and referred to two mycology referral laboratories in the north of Iran were included in the study. Identification of all dermatophyte isolates was confirmed by RFLP of rDNA internal transcribed spacer (ITS) regions. Antifungal susceptibility testing against five common antifungals using the CLSI-M38-A3 protocol was performed. The TMTISG isolates resistant to TRB, were further analyzed to determine the possible mutations in the SQLE gene. Totally, 647 cases (33%) were positive for dermatophytosis of which 280 cases (43.3%) were identified as members of TMTISG. These were more frequently isolated from tinea corporis 131 (44.56%) and tinea cruris 116 (39.46%). Of 280 TMTISG isolates, 40 (14.3%) were resistant to TRB (MIC ≥ 4 µg/mL), all found to be T. indotineae in ITS sequencing. In SQLE sequencing 34 (85%) of TRB-resistant isolates had coincident mutations of Phe397Leu and Ala448Thr whereas four and two isolates had single mutations of Phe397Leu and Leu393Ser, respectively. Overall, the resistance of Iranian TMTISG isolates to TRB greatly occurred by a mutation of Phe397Leu in the SQLE gene as alone or in combination with Ala448Thr. Nevertheless, for the occurrence of in vitro resistance, only the presence of Phe397Leu mutation seems to be decisive.

Mapping the Global Spread of T. indotineae: An Update on Antifungal Resistance, Mutations, and Strategies for Effective Management

INTRODUCTION

The global spread of Trichophyton indotineae presents a pressing challenge in dermatophytosis management. This systematic review explores the current landscape of T. indotineae infections, emphasizing resistance patterns, susceptibility testing, mutational analysis, and management strategies.

METHODS

A literature search was conducted in November 2023 using Embase, PubMed, Scopus, and Web of Science databases. Inclusion criteria covered clinical trials, observational studies, case series, or case reports with T. indotineae diagnosis through molecular methods. Reports on resistance mechanisms, antifungal susceptibility testing, and management were used for data extraction.

RESULTS AND DISCUSSION

A total of 1148 articles were identified through the systematic search process, with 45 meeting the inclusion criteria. The global spread of T. indotineae is evident, with cases reported in numerous new countries in 2023. Tentative epidemiological cut-off values (ECOFFs) suggested by several groups provide insights into the likelihood of clinical resistance. The presence of specific mutations, particularly Phe397Leu, correlate with higher minimum inhibitory concentrations (MICs), indicating potential clinical resistance. Azole resistance has also been reported and investigated in T. indotineae, and is a growing concern. Nevertheless, itraconazole continues to be an alternative therapy. Recommendations for management include oral or combination therapies and individualized approaches based on mutational analysis and susceptibility testing.

CONCLUSION

Trichophyton indotineae poses a complex clinical scenario, necessitating enhanced surveillance, improved diagnostics, and cautious antifungal use. The absence of established clinical breakpoints for dermatophytes underscores the need for further research in this challenging field.

Expert Panel Review of Skin and Hair Dermatophytoses in an Era of Antifungal Resistance

Dermatophytoses are fungal infections of the skin, hair, and nails that affect approximately 25% of the global population. Occlusive clothing, living in a hot humid environment, poor hygiene, proximity to animals, and crowded living conditions are important risk factors. Dermatophyte infections are named for the anatomic area they infect, and include tinea corporis, cruris, capitis, barbae, faciei, pedis, and manuum. Tinea incognito describes steroid-modified tinea. In some patients, especially those who are immunosuppressed or who have a history of corticosteroid use, dermatophyte infections may spread to involve extensive skin areas, and, in rare cases, may extend to the dermis and hair follicle. Over the past decade, dermatophytoses cases not responding to standard of care therapy have been increasingly reported. These cases are especially prevalent in the Indian subcontinent, and Trichophyton indotineae has been identified as the causative species, generating concern regarding resistance to available antifungal therapies. Antifungal-resistant dermatophyte infections have been recently recognized in the United States. Antifungal resistance is now a global health concern. When feasible, mycological confirmation before starting treatment is considered best practice. To curb antifungal-resistant infections, it is necessary for physicians to maintain a high index of suspicion for resistant dermatophyte infections coupled with antifungal stewardship efforts. Furthermore, by forging partnerships with federal agencies, state and local public health agencies, professional societies, and academic institutions, dermatologists can lead efforts to prevent the spread of antifungal-resistant dermatophytes.

An update on antifungal resistance in dermatophytosis

INTRODUCTION

The reports of resistance to antifungal agents used for treating onychomycosis and other superficial fungal infections are increasing. This rise in antifungal resistance poses a public health challenge that requires attention.

AREAS COVERED

This review explores the prevalence of dermatophytes and the current relationship between dermatophyte species, their minimum inhibitory concentrations (MICs) for terbinafine (an allylamine) and itraconazole (an azole), and various mutations prevalent in these species. The most frequently isolated dermatophyte associated with resistance in patients with onychomycosis and dermatophytosis was T. mentagrophytes. However, T. indotineae emerged as the most prevalent isolate with mutations in the SQLE gene, exhibiting the highest MIC of 8 µg/ml for terbinafine and MICs of 8 µg/ml and ≥ 32 µg/ml for itraconazole.Overall, the most prevalent SQLE mutations were Phe397Leu, Leu393Phe, Ala448Thr, Phe397Leu/Ala448Thr, and Lys276Asn/Leu415Phe (relatively recent).

EXPERT OPINION

Managing dermatophyte infections requires a personalized approach. A detailed history should be obtained including details of travel, home and occupational exposure, and clinical examination of the skin, nails and other body systems. Relevant testing includes mycological examination (traditional and molecular). Additional testing, where available, includes MIC evaluation and detection of SQLE mutations. In case of suspected terbinafine resistance, itraconazole or voriconazole (less commonly) should be considered.

Emerging Antifungal Resistance in Fungal Pathogens

Purpose of Review

Over recent decades, the number of outbreaks caused by fungi has increased for humans, plants (including important crop species) and animals. Yet this problem is compounded by emerging antifungal drug resistance in pathogenic species. Resistance develops over time when fungi are exposed to drugs either in the patient or in the environment.

Recent Findings

Novel resistant variants of fungal pathogens that were previously susceptible are evolving (such as Aspergillus fumigatus) as well as newly emerging fungal species that are displaying antifungal resistance profiles (e.g. Candida auris and Trichophyton indotineae).

Summary

This review highlights the important topic of emerging antifungal resistance in fungal pathogens and how it evolved, as well as how this relates to a growing public health burden.

Time to Think Antifungal Resistance Increased Antifungal Resistance Exacerbates the Burden of Fungal Infections Including Resistant Dermatomycoses

Increased antifungal resistance is exacerbating the burden of invasive fungal infections, as well as potentially contributing to the increase in resistant dermatomycoses. In this commentary, we focus on antifungal drug resistance, in contrast to antibacterial resistance. We provide a brief historical perspective on the emergence of antifungal resistance and propose measures for combating this growing health concern. The increase in the incidence of invasive and cutaneous fungal infections parallels advancements in medical interventions, such as immunosuppressive drugs, to manage cancer and reduce organ rejection following transplant. A disturbing relatively new trend in antifungal resistance is the observation of several fungal species that now exhibit multidrug resistance (eg, Candida auris, Trichophyton indotineae). Increasing awareness of these multidrug-resistant species is paramount. Therefore, increased education regarding potential fungus-associated infections is needed to address awareness in the general healthcare setting, which may result in a more realistic picture of the prevalence of antifungal-resistant infections. In addition to education, increased use of diagnostic tests (eg, micro and macro conventional assays or molecular testing) should be routine for healthcare providers facing an unknown fungal infection. Two critical barriers that affect the low rates for Antifungal Susceptibility Testing (AST) are low (or a lack of) sufficient insurance reimbursement rates and the low number of qualified laboratories with the capacity to perform AST. The ultimate aim is to improve the quality of patient care through fungal identification, diagnosis, and, where appropriate, susceptibility testing. Here we propose an all-encompassing call to action to address this emerging challenge.

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.

Multi-drug resistance Trichophyton indotineae in a stray dog

A 2.5-year-old stray dog showed signs of hair loss, mild skin crusting, and redness on extremities and trunk. The etiologic agent was confirmed as Trichophyton indotineae by sequencing of ITS region. Using the Clinical and Laboratory Standards Institute (CLSI M38-A3) guideline, antifungal susceptibility testing showed multidrug resistance phenotype against terbinafine (16 μg/mL-1), itraconazole, and some other tested antifungals (minimum inhibitory concentration, MIC≥16 μg/mL-1). However, luliconazole was found to be active in- vitro (0.016 μg/mL-1). Upon further studies, sequencing of SQLE gene showed an amino acids substitution of Phe397Leu and Ala448Thr, which is potentially linked to terbinafine resistance in Trichophyton species.

Lipid-Centric Approaches in Combating Infectious Diseases: Antibacterials, Antifungals and Antivirals with Lipid-Associated Mechanisms of Action

One of the global challenges of the 21st century is the increase in mortality from infectious diseases against the backdrop of the spread of antibiotic-resistant pathogenic microorganisms. In this regard, it is worth targeting antibacterials towards the membranes of pathogens that are quite conservative and not amenable to elimination. This review is an attempt to critically analyze the possibilities of targeting antimicrobial agents towards enzymes involved in pathogen lipid biosynthesis or towards bacterial, fungal, and viral lipid membranes, to increase the permeability via pore formation and to modulate the membranes' properties in a manner that makes them incompatible with the pathogen's life cycle. This review discusses the advantages and disadvantages of each approach in the search for highly effective but nontoxic antimicrobial agents. Examples of compounds with a proven molecular mechanism of action are presented, and the types of the most promising pharmacophores for further research and the improvement of the characteristics of antibiotics are discussed. The strategies that pathogens use for survival in terms of modulating the lipid composition and physical properties of the membrane, achieving a balance between resistance to antibiotics and the ability to facilitate all necessary transport and signaling processes, are also considered.

The rapid emergence of antifungal-resistant human-pathogenic fungi

During recent decades, the emergence of pathogenic fungi has posed an increasing public health threat, particularly given the limited number of antifungal drugs available to treat invasive infections. In this Review, we discuss the global emergence and spread of three emerging antifungal-resistant fungi: Candida auris, driven by global health-care transmission and possibly facilitated by climate change; azole-resistant Aspergillus fumigatus, driven by the selection facilitated by azole fungicide use in agricultural and other settings; and Trichophyton indotineae, driven by the under-regulated use of over-the-counter high-potency corticosteroid-containing antifungal creams. The diversity of the fungi themselves and the drivers of their emergence make it clear that we cannot predict what might emerge next. Therefore, vigilance is critical to monitoring fungal emergence, as well as the rise in overall antifungal resistance.

Detection of Squalene Epoxidase Mutations in United States Patients with Onychomycosis: Implications for Management

Resistance to oral terbinafine, the most commonly used antifungal to treat dermatophytosis and onychomycosis worldwide, is being increasingly reported. In this study, we aimed to investigate the species distribution and prevalence of squalene epoxidase mutations among toenail dermatophyte isolates. Samples from 15,683 patients suspected of onychomycosis visiting the offices of dermatologists and podiatrists in the United States were analyzed. Clinical information was reviewed, and dermatophyte species with or without squalene epoxidase mutations were detected using multiplex real-time PCRs. The frequency of dermatophytes was 37.6%; of isolates belonging to the Trichophyton genus, 88.3% were the T. rubrum complex, and 11.2% were the T. mentagrophytes complex. Individuals aged >70 years exhibited higher infection rates for the T. mentagrophytes complex. The overall mutation rate among Trichophyton spp. was 3.7%, with a higher mutation rate detected in the T. mentagrophytes complex (4.3 vs. 3.6%). Commonly detected mutations were T1189C/Phe397Leu (34.5%), T1306C/Phe415Ser (16.0%), and C1191A/Phe397Leu (11.0%). Squalene epoxidase gene mutations associated with decreased terbinafine susceptibility have been identified in United States patients with toenail onychomycosis. Physicians should be aware of the risk factors for resistance development and engage in antifungal stewardship practices such as directed diagnosis and treatment of dermatophytosis and onychomycosis.

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.

Autochthonous case of Trichophyton indotineae in Kuwait

Trichophyton indotineae is an emerging dermatophyte that has remarkable impact on public health worldwide. In addition to producing severe extensive skin lesions, this species is frequently resistant to terbinafine, used as a first line agent. As a result, the infection is often refractory, making treatment very challenging. The current report describes the first case of Trichophyton indotineae infection in Kuwait. The infected woman had no recent travel history. She failed to respond to several courses of antifungals, but finally responded to voriconazole. The report suggests that T. indotineae is under recognised, hence, active surveillance of dermatophytes is warranted.

[Recurrent tinea corporis generalisata due to Terbinafine-resistant Trichophyton rubrum strain : Long-term treatment with super bioavailability itraconazole]

For more than 30 years, an 82-year-old man has been suffering from tinea corporis generalisata in the sense of Trichophyton rubrum syndrome. The patient received long-term treatment with terbinafine. Fluconazole had no effect. There was an increase in liver enzymes with itraconazole. Super bioavailability (SUBA) itraconazole was initially not tolerated. A therapy attempt with voriconazole was successful, but was stopped due to side effects. The Trichophyton (T.) rubrum strain isolated from skin scales was tested for terbinafine resistance using the breakpoint method and found to be (still) sensitive. Sequencing of the squalene epoxidase (SQLE) gene revealed a previously unknown point mutation of the codon for isoleucine ATC→ACC with amino acid substitution I479T (isoleucine479 threonine). Long-term therapy with terbinafine 250 mg had been given every 3 days since 2018. In addition, bifonazole cream, ciclopirox solution, and occasionally terbinafine cream were used. The skin condition was stable until an exacerbation of the dermatophytosis in 2021. There were erythematosquamous, partly atrophic, centrifugal, scaly, confluent plaques on the integument and the extremities. Fingernails and toenails had white to yellow-brown discoloration, and were hyperkeratotic and totally dystrophic. T. rubrum was cultured from skin scales from the integument, from the feet, from nail shavings from the fingernails and also toenails and detected by PCR. In the breakpoint test, the T. rubrum isolates from tinea corporis and nail samples showed a minimum inhibitory concentration (MIC) of 0.5 µg ml-1 (terbinafine resistance in vitro). Sequencing of the SQLE gene of the T. rubrum isolate revealed evidence of a further point mutation that led to amino acid substitution I479V (isoleucine 479 valine). Long-term therapy was started with SUBA itraconazole: 14 days 2 × 1 capsule daily, then twice weekly administration of 2 × 50 mg. During breaks in therapy, the mycosis regularly flared up again. Finally, 50 mg SUBA itraconazole was given 5 days a week, which completely suppressed the dermatophytosis. Topically, ciclopirox and miconazole cream were used alternately. In conclusion, in the case of recurrent and therapy-refractory dermatophytoses caused by T. rubrum, terbinafine resistance must also be considered in individual cases. An in vitro resistance test and point mutation analysis of the squalene epoxidase gene confirms the diagnosis. Itraconazole, also in the form of SUBA itraconazole, is the drug of choice for the oral antifungal treatment of these patients.

Dermatophyte resistance - on the rise

Dermatophytes are group of filamentous fungi which have adapted to living on the skin of humans and other animals. In the last decade, reports have emerged from Asia of new dermatophyte strains showing resistance to the commonly used antifungal agent terbinafine and others. The spread of these resistant strains has been noted in many other countries globally. Little is known about the mechanisms or management of this emerging problem. Urgent research and changes to current practice are required if the spread of the infection is to be contained and managed effectively.

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.

Trichophyton: Changing Nomenclature and Practical Implications

Trichophyton interdigitale had been regarded as anthropophilic, mainly causing non-inflammatory tinea unguium and tinea pedis. T. mentagrophytes, thought to be zoophilic, were regarded as responsible for more inflammatory dermatophytosis. Indian terbinafine-resistant strains, identified with ribosomal internal transcribed spacer as 'genotype VIII', have recently been termed Trichophyton indotineae based on clinical and mycological features. Some of these have shown selective azole resistance as well. Phenotypic studies have shown some similarities and some differences between Trichophyton indotineae, T. mentagrophytes, and T. interdigitale, which are optimally distinguished with HMG locus analyses as three main genotypic groups containing the type strains of T. indotineae (CBS 146623), T. interdigitale (CBS 428.63), and T. mentagrophytes (IHEM 4268) and having approximate differences in geographic distribution. Trichophyton interdigitale was prevalently isolated from superficial infections on exposed body sites such as the scalp and face, while also feet and nails. Trichophyton mentagrophytes has a similar predilection but are also often found on the trunk and genitals. Trichophyton indotineae is mostly restricted to the trunk and groin. T. indotineae lesions are generally highly inflammatory, strongly associated with tinea cruris, corporis, and faciei and less commonly with fingernail onychomycosis and tinea pedis. They cause papulosquamous, pustular, pseudo-imbricata (tinea faciei), lichenoid, and pityriasis rosea (tinea corporis of the neck) types of lesions and spread rapidly to multiple sites and cause painful lesions with itching or burning. Lipolytic abilities of T. mentagrophytes and T. interdigitale are very similar and are higher than those of T. indotineae, which is associated with a higher prevalence of T. mentagrophytes on the human scalp, which is relatively rich in lipids. Keratin degradation is significantly larger in T. interdigitale due to location (tinea pedis and tinea unguium). Identification of T. indotineae through culture alone may not be sufficient for effective treatment decision-making; genetic analysis for resistance profiles is needed for optimum treatment selection. In India, steroid-induced suppression of local cellular immunity as well as an altered cutaneous microbiome provided a window of opportunity for the unique, multidrug-resistant species Trichophyton indotineae.

Therapeutic Updates on the Management of Tinea Corporis or Cruris in the Era of Trichophyton Indotineae: Separating Evidence from Hype-A Narrative Review

The emergence and spread of Trichophyton indotineae (T. indotineae) has led to a sea change in the prescription practices of clinicians regarding the management of dermatophytic skin infections. An infection easily managed with a few weeks of antifungals, tinea corporis or cruris, is now often chronic and recurrent and requires prolonged treatment. Rising resistance to terbinafine, with documented squalene epoxidase (SQLE) gene mutations, and slow clinical response to itraconazole leave clinicians with limited treatment choices. However, in these testing times, it is essential that the tenets of antifungal stewardship be followed in making therapeutic decisions, and that the existing armamentarium of antifungals be used in rationale ways to counter this extremely common cutaneous infection, while keeping the growing drug resistance among dermatophytes in check. This review provides updated evidence on the use of various systemic antifungals for dermatophytic infection of the glabrous skin, especially with respect to the emerging T. indotineae species, which is gradually becoming a worldwide concern.

Terbinafine-Resistant Dermatophytes and the Presence of Trichophyton indotineae in North America

Dermatophytes are common causes of skin, hair, and nail infections in humans. The most common species causing infections in humans are Trichophyton rubrum, Trichophyton mentagrophytes, and Trichophyton interdigitale. Outbreaks of recalcitrant dermatophytosis have been reported in parts of South Asia, including those caused by a hypervirulent and resistant species, Trichophyton indotineae. We evaluated the antifungal susceptibility profiles of dermatophytes received by our laboratory from institutions across North America between 2021 and 2022 and performed species identification for isolates deemed to demonstrate in vitro resistance. Susceptibility testing was performed by CLSI broth microdilution methods, and species identification was performed by DNA sequence analysis. During this 2-year period, 271 dermatophyte isolates were included, the majority of which demonstrated low MIC values for terbinafine (geometric mean [GM] and modal MIC, 0.031 μg/mL and 0.008 μg/mL, respectively) and the azoles itraconazole, posaconazole, and voriconazole (0.035 to 0.049 μg/mL and ≤0.03 μg/mL). However, 18.6% of the isolates tested were resistant to terbinafine (MIC ≥ 0.5 μg/mL), including 21 T. rubrum and 21 T. indotineae isolates. These isolates were received from several different states in the United States and two provinces in Canada. In contrast, resistance to itraconazole was relatively rare. We also searched our laboratory database for earlier isolates that were resistant to terbinafine and identified 3 additional T. indotineae isolates, the earliest of which was from 2017. These results demonstrate that terbinafine resistance in dermatophytes was relatively common over this 2-year period and that T. indotineae is present in multiple areas in North America. Continued surveillance is warranted.

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.

Trichophyton indotineae, from epidemiology to therapeutic

Trichophyton indotineae is a newly described dermatophyte species. This fungal pathogen has recently emerged in India and is responsible for chronic or recurrent widespread superficial infections. Resistance to terbinafine is frequently associated to this pathogen and is related to point mutations in the gene encoding the squalene epoxidase. T. indotineae infections have been reported outside India, highlighting the risk of worldwide diffusion of this microorganism. Species identification and antifungal susceptibility determination are key points for infection control but still remain challenging. Systemic treatment is usually required and itraconazole is frequently prescribed in case of terbinafine resistance. This review summarizes main features of T. indotineae taxonomy, epidemiology, clinical manifestations, identification, antifungal profile, treatment and prevention.

Onychomycosis: Old and New

Onychomycosis is a common chronic fungal infection of the nail that causes discoloration and/or thickening of the nail plate. Oral agents are generally preferred, except in the case of mild toenail infection limited to the distal nail plate. Terbinafine and itraconazole are the only approved oral therapies, and fluconazole is commonly utilized off-label. Cure rates with these therapies are limited, and resistance to terbinafine is starting to develop worldwide. In this review, we aim to review current oral treatment options for onychomycosis, as well as novel oral drugs that may have promising results in the treatment of onychomycosis.

Report of terbinafine resistant Trichophyton spp. in Italy: Clinical presentations, molecular identification, antifungal susceptibility testing and mutations in the squalene epoxidase gene

BACKGROUND

Numerous reports of resistance to terbinafine in Trichophyton spp. from all over the world are arousing justified attention and concern. Point mutations in the gene that encodes the squalene epoxidase (SQLE) enzyme are responsible for these therapeutic resistances.

OBJECTIVES

Primary objective of the study was to describe first isolates of Trichophyton spp. resistant to terbinafine among the patients treated between September 2019 and June 2022 at the Dermatology Units of Ospedale Maggiore Policlinico and San Bortolo Hospital. Secondary objective was to study the resistance mechanism.

METHODS

Patients with confirmed Trichophyton spp. infection has been treated with systemic and topical terbinafine. Patients were then re-evaluated 12 weeks after the therapy. Patients with incomplete or absent response to terbinafine underwent a new skin scraping for direct mycological examination, new identification of dermatophyte species from culture and MALDI-TOF, molecular species identification, antifungal susceptibility testing and molecular analysis of SQLE gene.

RESULTS

We identified five patients without clinical response to treatment with terbinafine. The DNA sequencing of the ITS region identified one Trichophyton rubrum and four Trichophyton indotineae. The T. rubrum strain showed minimum inhibitory concentration (MIC) (90% growth inhibition) of 4 mg/L for terbinafine. The four T. indotineae strains showed a MICs range of 0.25-4 mg/L for terbinafine. The analysis of the SQLE gene in the T. rubrum strain showed a nucleotide substitution generating a missense mutation (L393F). The SQLE gene sequencing in the T. indotineae strains showed a nucleotide substitution generating a missense mutation (F397L) in two strains, a nucleotide substitution L393S in one strain and a nucleotide substitution F415C in another strain.

CONCLUSIONS

We report the first cases of terbinafine-resistant Trichophyton isolates in the Italian population. Solid antifungal management programs will be needed to promote more responsible use of antimycotics and preserve their therapeutic efficacy to control antifungal resistance.

Potential Inhibitory Effect of Miltefosine against Terbinafine-Resistant Trichophyton indotineae

Several prolonged and significant outbreaks of dermatophytosis caused by Trichophyton indotineae, a new emerging terbinafine-resistant species, have been ongoing in India in recent years, and have since spread to various countries outside Asia. Miltefosine, an alkylphosphocholine, is the most recently approved drug for the treatment of both visceral and cutaneous leishmaniasis. Miltefosine in vitro activity against terbinafine-resistant and susceptible T. mentagrophytes/T. interdigitale species complex, including T. indotineae, is limited. The current study aimed to assess miltefosine's in vitro activity against dermatophyte isolates, which are the most common causes of dermatophytosis. Miltefosine, terbinafine, butenafine, tolnaftate, and itraconazole susceptibility testing was performed using Clinical and Laboratory Standards Institute broth microdilution methods (CLSI M38-A3) against 40 terbinafine-resistant T. indotineae isolates and 40 terbinafine-susceptible T. mentagrophytes/T. interdigitale species complex isolates. Miltefosine had MIC ranges of 0.063-0.5 µg/mL and 0.125-0.25 µg/mL against both terbinafine-resistant and susceptible isolates. In terbinafine-resistant isolates, the MIC₅₀ and MIC₉₀ were 0.125 µg/mL and 0.25 µg/mL, respectively, and 0.25 µg/mL in susceptible isolates. Miltefosine had statistically significant differences in MIC results when compared to other antifungal agents (p-value 0.05) in terbinafine-resistant strains. Accordingly, the findings suggest that miltefosine has a potential activity for treating infections caused by terbinafine-resistant T. indotineae. However, further studies are needed to determine how well this in vitro activity translates into in vivo efficacy.

First Terbinafine-Resistant Trichophyton indotineae Isolates with Phe397Leu and/or Thr414His Mutations in Turkey

Fungal infections of the skin, nails, and hair caused by dermatophyte species continue to be a worldwide concern. The increase in terbinafine-resistant superficial dermatophytosis has become a major concern over the last decade. In this report, we presented two cases of infection with terbinafine-resistant Trichophyton indotineae, the first diagnosis of this species in Turkey. One patient exhibited erythematous pruritic patches and plaques in the inguinal and gluteal regions, while the other patient showed annular erythematous scaly plaques in the bilateral posterior thigh and gluteal regions. One patient harbored a CD36 mutation. Both strains harbored the same amino acid substitution in the squalene epoxidase gene, whereas one isolate had another unknown mutation. Clinical improvement was observed with resveratrol treatment in the patient with the CD36 mutation but not in the other patient.

A Review of Antifungal Susceptibility Testing for Dermatophyte Fungi and It's Correlation with Previous Exposure and Clinical Responses

Background: An increase in the number of recurrent and recalcitrant dermatophytoses calls for a tool to guide the clinician to correlate in vitro minimum inhibitory concentration (MIC) data, antifungal treatment with clinical outcomes. This systematic review aims to explore a possible correlation between one aspect of this, previous antifungal exposure, and clinical outcomes. Methods: A systematic literature search for articles on previous antifungal treatment, treatment outcome, susceptibility methods used, organism (genus/species), and MIC values was conducted. Results: A total of 720 records were identified of which 19 articles met the inclusion criteria. Forty percent of the cases had contact with or travel to India, 28% originated from or had traveled to other countries where treatment unresponsive tinea infections had been reported. Tinea corporis was the most common clinical presentation and the species involved were Trichophyton (T.) indotineae and T. rubrum, followed by T. mentagrophyte/interdigitale complex and T. tonsurans. Nearly all patients had previously been exposed to one or more antifungals. The studies were too heterogeneous to perform a statistical analysis to test if previous antifungal exposure was related to resistance. Conclusions: Only a few studies were identified, which had both sufficient and robust data on in vitro susceptibility testing and clinical treatment failure. Further research on the value of susceptibility testing to improve clinical practice in the management of dermatophyte infections is needed.

Effect of Different Itraconazole Dosing Regimens on Cure Rates, Treatment Duration, Safety, and Relapse Rates in Adult Patients With Tinea Corporis/Cruris: A Randomized Clinical Trial

Importance

With worldwide emergence of recalcitrant and resistant dermatophytosis, itraconazole is increasingly being used as the first-line drug for treatment of tinea corporis/cruris (TCC). Apparent inadequacy with low doses has led to empirical use of higher doses and antifungal combinations.

Objective

To compare cure rates, treatment durations, safety profiles, and relapse rates of itraconazole 100, 200, and 400 mg/d for the treatment of TCC.

Design, Setting, and Participants

This double-blind randomized clinical trial included adult patients with treatment-naive TCC involving at least 5% body surface area. Patients were recruited from the dermatology outpatient department of a tertiary care hospital in New Delhi, India between March 1, 2020, and August 31, 2021.

Interventions

Patients were randomized to 1 of the 3 treatment groups. Biweekly blinded assessments were performed until cure or treatment failure. Posttreatment follow-up of at least 8 weeks was conducted to detect relapses.

Main Outcome and Measures

Cure rates, treatment durations, safety profiles, and relapse rates were assessed. Secondary outcomes included comparison of rapidity of clinical response and cost-effectiveness between groups.

Results

Of the 149 patients assessed, the mean (SD) age was 34.3 (12.2) years, 69 patients (46.4%) were women, and 80 patients (53.6%) were men. The difference in cure rate between the 100- and 200-mg groups was statistically nonsignificant (hazard ratio [HR], 1.44; 95% CI, 0.91-2.30; P = .12), while the difference between the 100- and 400-mg groups (HR, 2.87; 95% CI, 1.78-4.62; P < .001) and between the 200- and 400-mg groups (HR, 1.99; 95% CI, 1.28-3.09; P = .002) was statistically significant. Mean (SD) treatment durations were statistically significantly different between the 100- and 400-mg groups (7.7 [4.7] weeks vs 5.2 [2.6] weeks; P = .03) and between the 200- and 400-mg groups (7.2 [3.8] weeks vs 5.2 [2.6] weeks; P = .004), but the difference between the 100- and 200-mg groups was not statistically significant. A total of 55 patients (47.4%) relapsed after treatment. Relapse rates were comparable across groups. No patient discontinued treatment due to adverse effects. Treatment with the 200-mg dose incurred a 63% higher cost and 400 mg a 120% higher cost over 100 mg in achieving cure.

Conclusions and Relevance

In this randomized clinical trial, high overall efficacy was observed among the 3 itraconazole doses for treatment of TCC, but with prolonged treatment durations and considerable relapse rates. Treatment with the 200- and 100-mg doses did not differ significantly in efficacy or treatment durations, while 400 mg scored over the other 2 on these outcomes. Considerable additional cost is incurred in achieving cure with the 200- and 400-mg doses.

Trial Registration

Clinical Trials Registry of India Identifier: CTRI/2020/03/024326.

Correction: Astvad et al. Increasing Terbinafine Resistance in Danish Trichophyton Isolates 2019–2020. J. Fungi 2022, 8, 150

In paragraph four of the discussion in the original article [...]

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.

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.

OUP accepted manuscript

The increasing incidence and changing epidemiology of invasive fungal infections continue to present many challenges to their effective management. The repertoire of antifungal drugs available for treatment is still limited although there are new antifungals on the horizon. Successful treatment of invasive mycoses is dependent on a mix of pathogen-, host- and antifungal drug-related factors. Laboratories need to be adept at detection of fungal pathogens in clinical samples in order to effectively guide treatment by identifying isolates with acquired drug resistance. While there are international guidelines on how to conduct in vitro antifungal susceptibility testing, these are not performed as widely as for bacterial pathogens. Furthermore, fungi generally are recovered in cultures more slowly than bacteria, and often cannot be cultured in the laboratory. Therefore, non-culture-based methods, including molecular tests, to detect fungi in clinical specimens are increasingly important in patient management and are becoming more reliable as technology improves. Molecular methods can also be used for detection of target gene mutations or other mechanisms that predict antifungal drug resistance. This review addresses acquired antifungal drug resistance in the principal human fungal pathogens and describes known resistance mechanisms and what in-house and commercial tools are available for their detection. It is emphasized that this approach should be complementary to culture-based susceptibility testing, given the range of mutations, resistance mechanisms and target genes that may be present in clinical isolates, but may not be included in current molecular assays.

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.