Development of an agar-based screening method for terbinafine, itraconazole, and amorolfine susceptibility testing of Trichophyton spp.

Resistance in dermatophytes is an emerging global public health issue. We, therefore, developed an agar-based method for screening Trichophyton spp. susceptibility to terbinafine (TRB), itraconazole (ITC), and amorolfine (AMF) and validated it using molecularly characterized isolates. Α total of 40 Trichophyton spp. isolates, 28 TRB wild type (WT) (13 T. rubrum, 10 T. mentagrophytes, 5 T. interdigitale) and 12 TRB non-WT (7 T. rubrum, 5 T. indotineae) with different alterations in the squalene epoxidase (SQLE) gene, were used. The optimal test conditions (inoculum and drug concentrations, incubation time, and temperature) and stability over time were evaluated. The method was then applied for 86 WT Trichophyton spp. clinical isolates (68 T. rubrum, 7 T. interdigitale, 6 T. tonsurans, 5 T. mentagrophytes) and 4 non-WT T. indotineae. Optimal growth of drug-free controls was observed using an inoculum of 20 µL 0.5 McFarland after 5-7 days of incubation at 30°C. The optimal concentrations that prevented the growth of WT isolates were 0.016 mg/L of TRB, 1 mg/L of ITC, and 0.25 mg/L of AMF, whereas 0.125 mg/L of TRB was used for the detection of Trichophyton strong SQLE mutants (MIC ≥0.25 mg/L). The agar plates were stable up to 4 months. Inter-observer and inter-experimental agreement were 100%, and the method successfully detected TRB non-WT Trichophyton spp. strains showing 100% agreement with the reference EUCAST methodology. An agar-based method was developed for screening Trichophyton spp. in order to detect TRB non-WT weak and strong mutant isolates facilitating their detection in non-expert routine diagnostic laboratories.

Dual quantitative PCR assays for the rapid detection of Trichophyton indotineae from clinical samples.

Trichophyton indotineae is an emerging species of the Trichophyton mentagrophytes complex (TMC), responsible for an epidemic of widespread hairless skin infections that is frequently (50-70%) resistant to terbinafine. In order to initiate appropriate treatment as quickly as possible without waiting for culture positivity (10-15 days) and molecular identification from the strain, we developed a dual quantitative PCR (qPCR) for the direct detection of T. indotineae in clinical samples. We first designed a T. indotineae-specific qPCR assay (TI-qPCR) targeting a single specific polymorphism in the internal transcribed spacer region. Although none of the 94 non-dermatophyte and 7 dermatophyte species were amplified, this TI-qPCR allowed amplification of other TMC species at a lower yield. With equal amounts (0.1 ng) of DNA per reaction, the mean quantitative cycle (Cq) values for T. indotineae and non-indotineae TMC were 27.9 (±0.1) and 38.9 (±0.3), respectively. Therefore, we normalized this assay against a previously validated pan-dermatophyte qPCR assay (PD-qPCR) and relied on the ΔCq [(TI-qPCR) - (PD-qPCR)] to identify T. indotineae versus other TMC species. Dual assay was validated using 86 clinical samples of culture-confirmed T. indotinea and 19 non-indotineae TMC cases. The mean ΔCq for non-indotineae TMC was 9.6 ± 2.7, whereas the ΔCq for T. indotinea was -1.46 ± 2.1 (P < .001). Setting the ΔCq at 4.5 as a cutoff value resulted in 100% specificity for the detection of T. indotineae. This dual qPCR assay quickly detects T. indotineae from skin scrapings, aiding in early diagnosis and treatment for patients with suspected infection.

Identifying the emerging species Trichophyton indotineae is long and requires to wait for culture positivity. We developed a dual qPCR strategy to detect T. indotineae directly from clinical sample with a 100% sensitivity.

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.

Molecular Detection of Dermatophytes and Nondermatophytes in Onychomycosis in Antalya, Turkey.

BACKGROUND: Onychomycosis is a chronic nail infection, and dermatophytes, yeasts, and nondermatophytic molds may be the causative agents. This study aimed to determine the etiological agents of onychomycosis by using conventional and molecular methods. METHODS: Between June 2020 and July 2021, 37 patients with a presumptive diagnosis of onychomycosis and mycological evidence (culture and/or EUROArray Dermatomycosis assay) were included in the study. Organisms detected in cultured nail specimens were identified by combined phenotypic characteristics and by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). An EUROarray Dermatomycosis assay was used for molecular detection of fungal pathogens. RESULTS: The EUROArray Dermatomycosis assay was positive for a single fungal target in 23 samples, and 14 samples were positive by culture. The most common pathogen was Trichophyton rubrum in both methods. Coinfection was detected in 14 samples by using molecular methods, and Trichophyton rubrum and Fusarium solani (9 samples) were the most common pathogens detected together. Trichophyton spp., nondermatophyte molds, and Candida spp. were detected in 33 (89.2%), 16 (43.2%), and 6 (16.2%) samples, respectively, when the two methods were evaluated together. CONCLUSIONS: Our results revealed that fungal culture allows the diagnosis of onychomycosis, but it is not as sensitive as the EUROArray Dermatomycosis test, especially in patients receiving antifungal therapy.

Prolonged treatment of dermatophytosis caused by Trichophyton indotinea with terbinafine or itraconazole impacts better outcomes irrespective of mutation in the squalene epoxidase gene.

BACKGROUND: Over the past decades, the increasing incidence of recurrent dermatophytosis associated with terbinafine-resistant Trichophyton has posed a serious challenge in management of dermatophytosis. Independent reports of failure of treatment and high minimum inhibitory concentrations (MIC) of antifungals are available, but data correlating MIC and clinical outcomes is still sparse. Therefore, the present study was conducted to evaluate the outcomes of systemic treatment of dermatophytosis and its correlation with MIC of the etiological agents isolated from such patients. METHODS: Retrospective analysis of 587 consecutive patients with dermatophytosis was done from March 2017 to March 2019. Demographic and clinical details of the patients were noted, along with the results of direct microscopy and fungal culture. The isolates were identified by sequencing the internal transcribed spacer region of rDNA. Antifungal susceptibility testing was performed following the CLSI M38 protocol. Mutation in the squalene epoxidase (SE) gene was detected by DNA sequencing and ARMS-PCR. Based on the culture-positivity and prescribed systemic antifungal, patients were categorised into Group I culture-positive cases treated with systemic terbinafine and Group II culture-positive cases treated with systemic itraconazole, each for a total period of 12 weeks. RESULTS: In the present study, 477 (81.39%) were culture-positive; however, 12 weeks follow-up was available for 294 patients (Group I-157 and Group II-137) who were included for statistical analysis. In both groups [Group I-37/63 (51.4%) and Group II-14/54 (58.3%)], a better cure rate was observed if the initiation of therapy was performed within <6 months of illness. Treatment outcome revealed that if therapy was extended for 8-12 weeks, the odds of cure rate are significantly better (p < .001) with either itraconazole (Odd Ratio-15.5) or terbinafine (Odd Ratio-4.34). Higher MICs for terbinafine were noted in 41 cases (cured-18 and uncured-23) in Group I and 39 cases (cured-16 and uncured-23) in Group II. From cured (Group I-17/18; 94.4% and Group II-14/16; 87.5%) and uncured (Group I-20/23; 86.9% and Group II-21/23; 91.3%) cases had F397L mutation in the SE gene. No significant difference in cure rate was observed in patients with Trichophyton spp. having terbinafine MIC ≥ 1or <1 µg/mL (Group I-p = .712 and Group II-p = .69). CONCLUSION: This study revealed that prolonging terbinafine or itraconazole therapy for beyond 8 weeks rather than the standard 4 weeks significantly increases the cure rate. Moreover, no correlation has been observed between antifungal susceptibility and clinical outcomes. The MIC remains the primary parameter for defining antifungal activity and predicting the potency of antifungal agents against specific fungi. However, predicting therapeutic success based solely on the MIC of a fungal strain is not always reliable, as studies have shown a poor correlation between in vitro data and in vivo outcomes. To address this issue, further correlation of antifungal susceptibility testing (AFST) data with clinical outcomes and therapeutic drug monitoring is needed. It also highlights that initiation of the treatment within <6 months of illness increases cure rates and reduces recurrence. Extensive research is warranted to establish a better treatment regime for dermatophytosis.

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.

Resistance Profile, Terbinafine Resistance Screening and MALDI-TOF MS Identification of the Emerging Pathogen Trichophyton indotineae.

The emerging pathogen Trichophyton indotineae, often resistant to terbinafine (TRB), is known to cause severe dermatophytoses such as tinea corporis and tinea cruris. In order to achieve successful treatment for these infections, insight in the resistance profile of T. indotineae strains and rapid, reliable identification is necessary. In this research, a screening medium was tested on T. indotineae strains (n = 20) as an indication tool of TRB resistance. The obtained results were confirmed by antifungal susceptibility testing (AST) for TRB following the in vitro broth microdilution reference method. Additionally, AST was performed for eight other antifungal drugs: fluconazole, itraconazole, voriconazole, ketoconazole, griseofulvin, ciclopirox olamine, naftifine and amorolfine. Forty-five percent of the strains were confirmed to be resistant to terbinafine. The TRB resistant strains showed elevated minimal inhibitory concentration values for naftifine and amorolfine as well. DNA sequencing of the squalene epoxidase-encoding gene showed that TRB resistance was a consequence of missense point mutations in this gene, which led to amino acid substitutions F397L or L393F. MALDI-TOF MS was used as a quick, accurate identification tool for T. indotineae, as it can be challenging to distinguish it from closely related species such as Trichophyton mentagrophytes or Trichophyton interdigitale using morphological characteristics. While MALDI-TOF MS could reliably identify ≥ 95% of the T. indotineae strains (depending on the spectral library), it could not be used to successfully distinguish TRB susceptible from TRB resistant strains.

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.

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.

Sexually Transmitted Trichophyton mentagrophytes Genotype VII Infection among Men Who Have Sex with Men.

Transmission of dermatophytes, especially Trichophyton mentagrophytes genotype VII, during sexual intercourse has been recently reported. We report 13 such cases in France. All patients were male; 12 were men who have sex with men. Our findings suggest sexual transmission of this pathogen within a specific population, men who have sex with men.

Metabolic phenotype analysis of Trichophyton rubrum after laser irradiation.

BACKGROUND: Biological phenotypes are important characteristics of microorganisms, and often reflect their genotype and genotype changes. Traditionally, Trichophyton rubrum (T. rubrum) phenotypes were detected using carbon source assimilation tests, during which the types of tested substances are limited. In addition, the operation is complicated, and only one substance can be tested at once. To observe the changes of the metabolic phenotype of T. rubrum after laser irradiation, a high-throughput phenotype microarray system was used to analyze the metabolism of different carbon, nitrogen, phosphorus and sulfur source substrates in a Biolog metabolic phenotyping system. RESULTS: The strain of T. rubrum used in this study can effectively utilize 33 carbon, 20 nitrogen, 16 phosphorus, and 13 sulfur source substrates prior to laser irradiation. After laser irradiation, the strain was able to utilize 10 carbon, 12 nitrogen, 12 phosphorus, and 8 sulfur source substrates. The degree of utilization was significantly decreased compared with the control. Both groups efficiently utilized saccharides and organic acids as carbon sources as well as some amino acids as nitrogen sources for growth. The number of substrates utilized by T. rubrum after laser irradiation were significantly reduced, especially carbon substrates. Some substrates utilization degree in the laser treated group was higher than control, such as D-glucosamine, L-glutamine, D-2-Phospho-Glyceric Acid, D-glucosamine-6-phosphate, and D-methionine. CONCLUSION: Laser irradiation of T. rubrum may lead to changes in the metabolic substrate and metabolic pathway, thus weakening the activity of the strain.

Differential deuterolysin expression with a peak at low pH in human pathogenic fungi Trichophyton rubrum and T. mentagrophytes.

Trichophyton rubrum and T. mentagrophytes are the most common agents of dermatomycosis, a disease affecting millions worldwide. It has been widely recognized that secreted proteases are a key factor for host colonization. Dermatophytes have an unusually high amount of secreted protease, differentially expressed, and influenced by various conditions. This study analyzed the rule and expression of secreted deuterolysin protease of the M35 protein family in these two representative dermatophyte species. All strains secreted protease and could grow on keratin as the sole carbon and nitrogen source. Adding glucose to the keratin medium reduced the growth rate. Deuterolysin genes were most strongly expressed at acid conditions. NPIIc and NPIId expression was significantly higher than the other three deuterolysins. NPIIc had a high expression level in the two T. rubrum strains but a low expression in T. mentagrophytes strains. Both T. mentagrophytes strains had a high NPIId expression at low pH. NPIIc and NPIId deletion in T. rubrum caused a minor reduction in total protease activity, indicating the redundancy of protease in dermatophytes. It was postulated that protease gene enrichment in dermatophytes allows a sophisticated regulation of protease secretion to cope with changing conditions.

Nail infections and ringworm are caused by fungi called dermatophytes. About 20% of the world's population suffers from it at least once. Dermatophytes secrete skin protein-digesting enzymes. This study demonstrates the changing enzyme profile in response to different pH levels.

Clinical evaluation of a dermatophyte RT-PCR assay and its impact on the turn-around-time: A prospective study.

Onychomycosis is an important public health problem whose prevalence continues to grow and impact public health at several levels. Nevertheless, today the main diagnostic methods used in routine practice have many drawbacks. The aim of this study was to evaluate, for the first time, the clinical performance of a new multiplex polymerase chain reaction (PCR) (Novaplex®) in the identification of the causative agent on nail samples, and its impact on the turnaround time, compared to our traditional laboratory methods. From June 2022 to December 2022, all nail samples sent to our laboratory for suspected onychomycosis were included in this prospective study. We collected for each sample the results obtained with the Novaplex® PCR method and with the traditional direct microscopy examination and culture. Each discordant result was checked using a third method, which is another PCR method (DermaGenius® kit) as a resolver. For culture-positive samples, a turnaround time was calculated and compared to the one obtained with the Novaplex® method. A total of 131 samples were included. Among them, 5 were positive (3.8%) on direct microscopy, 33 were positive (25.2%) after culture, and 98 were negative (74.8%). All positive (n = 33) and negative (n = 69) cultures were also positive/negative with the Novaplex® PCR. Twenty-nine samples were positive with the Novaplex® method but negative with culture (discordant results). The percentage agreement between the culture and the Novaplex® methods was 77.9% (102 out of 131). While tested with the resolver (DermaGenius® PCR), 28 out of 29 discordant results were similarly found positive. The percentage agreement between the two PCR methods (Novaplex® and DermaGenius®) was 96.6%. The Novaplex® PCR method evaluated proved to be very reliable and allowed the direct identification of 62 out of 131 positive samples (47.3%) with the following distribution: 79.0% of Trichophyton rubrum complex, 11.3% of Trichophyton mentagrophytes complex, 6.5% of both Trichophyton rubrum complex and Trichophyton mentagrophytes complex, and 3.2% of Candida albicans. The median time [± 95% CI] for positive culture (between incubation and validation of the final identification) was 15 [12-23] days, while the turnaround time for the Novaplex® method adapted to our clinical laboratory routine is ≤7 days. Laboratory confirmation of onychomycosis is crucial and should always be obtained before starting treatment. The evaluated PCR method offered a rapid, reliable, robust, and inexpensive method of identification of the causative agent compared to traditional methods.

The aim of this study was to evaluate the clinical performance of a multiplex PCR in the identification of the causative agent of onychomycosis on nail samples, and its impact on the turnaround time, compared to our traditional laboratory methods. This new method is rapid, reliable, robust, and inexpensive.

Molecular detection and species identification of dermatophytes by SYBR-Green real-time PCR in-house methodology using hair samples obtained from dogs and cats.

The classical dermatophytes diagnosis is based on mycological culture and microscopy observation both human and animal hair, skin, and nail samples. The aim of this work was to develop the new in-house real-time PCR with pan-dematophyte reaction for detection and identification of the main dermatophytes directly from hair samples, providing a simple and rapid diagnosis of dermatophytosis in dogs and cats. An in-house SYBR-Green real-time PCR was designed and used for detecting a DNA fragment encoding chitin synthase 1 (CHS1). A total of 287 samples were processed by culture, microscopic examination with KOH 10%, and real-time PCR (qPCR) analysis. Melting curve analysis of the CHS1 fragment revealed to be reproducible, showing a single distinct peak for each species of dermatophyte, namely Trichophyton mentagrophytes, T. verrucosum, Microsporum canis, and Nannizzia gypsea (formerly M. gypseum). Then, out of the 287 clinically suspected cases of dermatophytosis, 50% were positive for dermatophytes by qPCR, 44% by mycological culture, and 25% by microscopic examination. Microsporum canis was identified in 117 samples tested by culture and 134 samples tested by qPCR, followed by N. gypsea in 5 samples (either tested by culture or qPCR) and T. mentagrophytes detected in 4 and 5 samples when tested by culture or qPCR, respectively. Overall, qPCR allowed the diagnosis of dermatophytosis in clinical samples. The results suggest this newly proposed in-house real-time PCR assay can be used as alternative diagnosis and rapid identification of dermatophytes frequently associated to clinical hair samples of dogs and cats.

The aim of this work was to develop a molecular detection strategy for dermatophytes by SYBR-Green real-time PCR of hair samples from animals. The melting curve analysis of the CHS1 fragment revealed to be reproducible, showing a single distinct peak for distinct dermatophyte species and allowed the diagnosis of dermatophytosis in dogs and cats caused mainly by Trichophyton mentagrophytes, Microsporum sp., and Nannizzia gypsea).

Erythroderma combined with deeper dermal dermatophytosis due to Trichophyton rubrum in a patient with myasthenia gravis: first case report and literature review.

BACKGROUND: Dermatophytes are the most common causative pathogens of mycoses worldwide and usually cause superficial infections. However, they can enter deep into the dermis lead to invasive dermatophytosis such as deeper dermal dermatophytosis on rare occasions. Erythroderma is a severe dermatological manifestation of various diseases resulting in generalized skin redness, but erythroderma due to fungi infections is barely reported. In this article, we reported the first case of erythroderma combined with deeper dermal dermatophytosis due to Trichophyton rubrum (T. rubrum) in a patient with myasthenia gravis. CASE PRESENTATION: A 48-year-old man was hospitalized because of erythema with scaling and nodules covering his body for a month. The patient had a history of myasthenia gravis controlled by regularly taking prednisolone for > 10 years and accompanied by onychomycosis and tinea pedis lasting > 8 years. Based on histopathological examinations, fungal cultures, and DNA sequencing results, the patient was finally diagnosed with dermatophyte-induced erythroderma combined with deeper dermal dermatophytosis caused by T. rubrum. After 2 weeks of antifungal treatment, the patient had recovered well. CONCLUSIONS: This case report shows that immunosuppressed patients with long histories of superficial mycoses tend to have a higher risk of developing invasive dermatophytic infections or disseminated fungal infections. Dermatologists should be alert to this condition and promptly treat the superficial dermatophytosis.

Reliable and rapid identification of terbinafine resistance in dermatophytic nail and skin infections.

BACKGROUND: Fungal infections are the most frequent dermatoses. The gold standard treatment for dermatophytosis is the squalene epoxidase (SQLE) inhibitor terbinafine. Pathogenic dermatophytes resistant to terbinafine are an emerging global threat. Here, we determine the proportion of resistant fungal skin infections, analyse the molecular mechanisms of terbinafine resistance, and validate a method for its reliable rapid identification. METHODS: Between 2013 and 2021, we screened 5634 consecutively isolated Trichophyton for antifungal resistance determined by hyphal growth on Sabouraud dextrose agar medium containing 0.2 µg/mL terbinafine. All Trichophyton isolates with preserved growth capacity in the presence of terbinafine underwent SQLE sequencing. Minimum inhibitory concentrations (MICs) were determined by the broth microdilution method. RESULTS: Over an 8-year period, the proportion of fungal skin infections resistant to terbinafine increased from 0.63% in 2013 to 1.3% in 2021. Our routine phenotypic in vitro screening analysis identified 0.83% (n = 47/5634) of Trichophyton strains with in vitro terbinafine resistance. Molecular screening detected a mutation in the SQLE in all cases. Mutations L393F, L393S, F397L, F397I, F397V, Q408K, F415I, F415S, F415V, H440Y, or A398 A399 G400 deletion were detected in Trichophyton rubrum. Mutations L393F and F397L were the most frequent. In contrast, all mutations detected in T. mentagrophytes/T. interdigitale complex strains were F397L, except for one strain with L393S. All 47 strains featured significantly higher MICs than terbinafine-sensitive controls. The mutation-related range of MICs varied between 0.004 and 16.0 µg/mL, with MIC as low as 0.015 µg/mL conferring clinical resistance to standard terbinafine dosing. CONCLUSIONS: Based on our data, we propose MIC of 0.015 µg/mL as a minimum breakpoint for predicting clinically relevant terbinafine treatment failure to standard oral dosing for dermatophyte infections. We further propose growth on Sabouraud dextrose agar medium containing 0.2 µg/mL terbinafine and SQLE sequencing as fungal sporulation-independent methods for rapid and reliable detection of terbinafine resistance.

Clonal Outbreak of Trichophyton tonsurans Causing Tinea Capitis Among a Wrestling Team in Beijing, China.

Trichophyton tonsurans mostly causes tinea capitis and tinea corporis and often associates with outbreaks among combat sports athletes. Here, we report an outbreak of tinea capitis caused by T. tonsurans among five juvenile athletes in a wrestling team in Beijing, China. Scrapings from the lesions of the five patients were performed by direct microscopic examination and fungal culture. The fungal pathogens were all identified as T. tonsurans by morphology and sequencing of the internal transcribed spacer (ITS) regions. Multilocus genotyping analysis was performed by sequencing of 13 gene loci. The sequences of these markers were identical among the five isolates, revealing a single genotype. Antifungal susceptibilities of terbinafine, itraconazole, fluconazole, ketoconazole, and amphotericin B against T. tonsurans was determined by broth microdilution method according to the Clinical and Laboratory Standards Institute M38-A3 document and these isolates were all susceptible to the common antifungal drugs treating tinea capitis.

Genomic Analysis of Antifungal Drug Resistance Induced in Trichophyton rubrum After Prolonged Culture with Terbinafine.

In this study, we induced terbinafine (TRF) resistance in a T. rubrum strain in vitro for 18 months then compared the genomes of the TRF-resistant (N42-3) and TRF-susceptible wild-type (N42WT) strains to identify mutations. In the SQLE gene, N42WT had no mutation while N42-3 had a F397L mutation. We sequenced approximately 22.53 Mb of the genomes of the N43WT and N42-3 strains. Other than the F397L mutation in SQLE, there were three other genetic mutations in three different genes that were found in N42-3, but not in N43WT; however, these three mutations were not detected in other TRF-resistant T. rubrum strains. From this genome sequencing analysis, the only variation that was confirmed to be associated with drug resistance in the genome of the TRF-resistant T. rubrum was a hotspot mutation in SQLE.

Long Amplification PCR (LA-PCR) Detection of Azole Resistant Trichophyton indotineae.

Trichphyton indotineae, a species newly designated in 2020 independent of T. interdigitale, comprises highly terbinafine (TRF)-resistant dermatophytosis that is epidemic in North India and spreding to worldwide. Some clinical isolates of T. indotineae have been resistance both TRF and azoles that might be caused the treatment failure. To detect the azole resistance strains, we developed a long amplification PCR (LA-PCR) detection method for the tandem repeat of the CYP51B (encoding sterol 14a-demethylase gene) in T. indotineae. Contrasting the drug susceptibility test results with the LA-PCR results confirmed a trend toward low susceptibility to azole antifungal agents in strains with amplifications of 9.5 kbp or greater (3 or more copies of CYP51B). Our results suggest that the method could be detected rapidly of low-susceptibility strains to azole antifungal agents.

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.