Itraconazole resistance of Trichophyton rubrum mediated by the ABC transporter TruMDR2

Widespread Majocchi's Granuloma Caused by Multidrug-Resistant Trichophyton rubrum Successfully Treated With Amphotericin B and Posaconazole

We encountered a 60-year-old Japanese female patient with disseminated dermatophytosis caused by terbinafine-resistant Trichophyton rubrum with mutant SQLE (Leu393Phe substitution). Histopathology showed fungus in the dermis, indicating Majocchi granuloma. Oral fosravuconazole and topical luliconazole were administered for 18 months, resulting in invasive dermatophytosis with a high β-d-glucan level of 7320 pg/mL. The MICs of amphotericin B, posaconazole, griseofulvin, itraconazole, voriconazole, ravuconazole, and terbinafine were 0.5, 0.5, 8, 16, 8, 16, and 32 μg/mL, respectively. Amphotericin B for 6 months followed by oral posaconazole for another 6 months cured the disease. Posaconazole may be a promising agent for the treatment of multidrug-resistant dermatophytes. We present the first reported case of multiazole-resistant T. rubrum resulting from prolonged fosravuconazole treatment.

Comparative functional analysis of a new CDR1-like ABC transporter gene in multidrug resistance and virulence between Magnaporthe oryzae and Trichophyton mentagrophytes

Fungi are notorious for causing diseases in plants and domestic animals. ABC transporters play pivotal roles in multidrug resistance in fungi, with some ABC proteins indispensable for the pathogenicity of plant fungal pathogens. However, the roles of ABC proteins in animal pathogenic fungi, and the functional connections between ABC homologues in plant and animal pathogenic fungi are largely obscure. Here, we identified a new ABCG-1 gene, MoCDR1, in rice-blast fungus Magnaporthe oryzae. MoCDR1 disruption caused hypersensitivity to multidrugs, and impaired conidiation, appressorium formation, and pathogenicity. Subsequently, we systematically retrieved ABC proteins in animal pathogenic fungus Trichophyton mentagrophytes and identified TmCdr1, a homologue to MoCdr1. TmCDR1 effectively rescued the drug sensitivity and virulence of ΔMocdr1 and mediated the drug resistance and animal skin infection in T. mentagrophytes. Moreover, MoCDR1 also rescued the defects in drug sensitivity and virulence of ΔTmcdr1. MoCdr1 and TmCdr1 are conserved in structures and functions, and both involved in drug resistance and pathogenicity by analogously regulating gene expression levels related to transporter activity, MAPK signaling pathway, and metabolic processes. Altogether, our results represent the first comprehensive characterization of ABC genes in T. mentagrophytes, establishing a functional correlation between homologous ABC genes in plant and animal pathogenic fungi.

Strategy to Identify Virulence-Related Genes of the Pathogenic Fungus Trichosporon asahii Using an Efficient Gene-Targeting System

Trichosporon asahii is a pathogenic fungus that causes severe deep-seated mycosis in immunocompromised patients with neutropenia. Understanding the molecular mechanisms of T. asahii infection will facilitate the development of new therapeutic and preventive strategies. Two main obstacles have prevented the identification of virulence-related genes in T. asahii using molecular genetic techniques: the lack of experimental animal infection models for easy evaluation of T. asahii virulence and the lack of genetic recombination technology for T. asahii. To address these issues, we developed a silkworm infection model to quantitatively evaluate T. asahii virulence and a genetic recombination method to generate gene-deficient T. asahii mutants, enabling the identification of virulence factors of T. asahii. In this review, we propose a strategy for identifying virulence-related factors in T. asahii using a silkworm infection model and an efficient gene-targeting system.

Mechanisms of resistance against allylamine and azole antifungals in Trichophyton: A renewed call for innovative molecular diagnostics in susceptibility testing

The emergence of antifungal resistance calls for continued research efforts to better guide healthcare providers in treatment selection and outcomes. Unlike bacterial infections, treatment of superficial fungal infections is mainly limited to allylamines (terbinafine) and azoles (itraconazole). Here, we aim to update our current understanding of resistance mechanisms against allylamine and azole antifungals in the Trichophyton genus. Resistance development has been demonstrated in vitro by challenging Trichophyton isolates with allylamines or azoles at levels below the minimum inhibitory concentration (MIC), which corroborates the observation of clinical resistance. Frequently reported mechanisms of resistance include: (I) Alterations of the drug target by single-nucleotide variations (SNVs) of the SQLE/ERG1 and ERG11 genes; in particular, SQLE SNVs (Leu393Phe, Leu393Ser, and Phe397Leu) have been frequently reported in isolates with high terbinafine MICs; (II) overexpression of the target enzyme for azoles (ERG11) and downstream genes in the ergosterol biosynthesis pathway can decrease the effective drug concentration as well as prevent the depletion of ergosterol and the accumulation of toxic sterol intermediates; (III) the up-regulation of drug efflux channels-belonging to the ABC superfamily (PDR1, MDR2, MDR3, MDR4), MFS superfamily (MFS1), or Pma1 (plasma membrane ATPase 1)-can reduce the effective concentrations of terbinafine and azoles. The possibility of multidrug resistance has been shown in Trichophyton strains, of both human and animal origins, harboring multiple resistance mechanisms (e.g., target alteration/overexpression and drug efflux channels). Tackling the issue of antifungal resistance will require an integrated approach with multidisciplinary efforts including surveillance initiatives and antifungal stewardship programs. However, these efforts are hampered by the current limited accessibility of antifungal susceptibility testing as well as the limited choice of antifungals available in routine practice. A better understanding of resistance mechanisms could help develop targeted, molecular-based assays.

Dermatophytes: Update on Clinical Epidemiology and Treatment

Dermatophytes represent the largest and most common group of fungal infections, impacting 25% of the global population. Among them, Trichophyton rubrum has emerged as the predominant species, responsible for a range of conditions such as tinea corporis, tinea pedis, onychomycosis, tinea cruris, and tinea manuum. Although dermatophyte incidence varies geographically, there is a noticeable rise in cases caused by T. indotineae, a strain that exhibits resistance to terbinafine. In the past decade zoophilic dermatophyte T. mentagophytes genotype VII (now known as T. interdigitale) gains a growing importance, due to its increasing frequency, the severity of the clinical manifestation and mode of transmission. Tinea infections present with various clinical symptoms and can affect individuals of all ages, from tinea pedis in adults to tinea capitis in children. Among adults globally, tinea unguium (onychomycosis) is the most common form of dermatophytosis, affecting 5.5% of the general population. Tinea unguium is more frequently seen in developed countries, while tinea capitis is more common in developing nations. The COVID-19 pandemic has led to an increase in cases of tinea faciei, likely due to prolonged mask-wearing. Terbinafine remains the preferred treatment for dermatophyte infections worldwide due to its potent fungicidal properties, minimal risk of drug interactions, and fewer side effects compared to other oral antifungals. Itraconazole and terbinafine appear to be equally effective and safe for treating tinea cruris and tinea corporis. However, the rising resistance of dermatophytes to these antifungal drugs, along with frequent recurrences of dermatophytosis in certain regions, is becoming a significant public health concern.

Combinatorial effect of fluconazole, itraconazole, and terbinafine with different culture extracts of Candida parapsilosis and Trichophyton spp. against Trichophyton rubrum

Onychomycosis is a nail infection caused by dermatophytes, non-dermatophyte fungi, and yeasts, especially Candida species. The present study evaluated the combinatorial effect of different cultured extracts of Candida parapsilosis and Trichophyton mentagrophytes and Trichophyton rubrum with fluconazole, itraconazole, and terbinafine against clinical isolates of Trichophyton rubrum. In addition, investigation of the action of the extracts on the wall or membrane was performed. Pure and mixed cultures of Candida parapsilosis and dermatophytes were filtered through a 0.2-μm membrane and submitted to liquid-liquid extraction using ethyl acetate. After a checkerboard, trial with drugs was performed to evaluate the synergistic interaction with the extract. The results obtained for the minimum inhibitory concentration (MIC) of extracts against the T. rubrum strain in isolation were 500-8000 μg/mL. The MIC range for fluconazole, itraconazole, and terbinafine were 2-32 μg/mL, 0.25-0.5 μg/mL, 0.03-64 μg/mL, respectively. However, when the extract was combined with drugs, the MIC values decreased: extracts 1.9-1000 μg/mL, fluconazole 0.25-4, itraconazole 0.03-0.06 μg/mL, and terbinafine 0.001-0.02 μg/mL. The MIC values of the extracts in the Roswell Park Memorial Institute 1640 medium (RPMI) supplemented with sorbitol did not change, suggesting any action on the cell wall. However, in the presence of RPMI supplemented with ergosterol, MIC values of the extracts increased by up to 2×, indicating action on the fungal cell membrane. A synergistic action was observed between products and drugs, detecting a decrease in MIC values. There is potential and a new therapeutic perspective for fungal control.

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.

The StuA Transcription Factor and Alternative Splicing Mechanisms Drive the Levels of MAPK Hog1 Transcripts in the Dermatophyte Trichophyton rubrum

Trichophyton rubrum is a human fungal pathogen that causes dermatophytosis, an infection that affects keratinized tissues. Integrated molecular signals coordinate mechanisms that control pathogenicity. Transcriptional regulation is a core regulation of relevant fungal processes. Previous RNA sequencing data revealed that the absence of the transcription factor StuA resulted in the differential expression of the MAPK-related high glycerol osmolarity gene (hog1) in T. rubrum. Here we validated the role of StuA in regulating the transcript levels of hog1. We showed through RT-qPCR that transcriptional regulation controls hog1 levels in response to glucose, keratin, and co-culture with human keratinocytes. In addition, we also detected hog1 pre-mRNA transcripts that underwent alternative splicing, presenting intron retention in a StuA-dependent mechanism. Our findings suggest that StuA and alternative splicing simultaneously, but not dependently, coordinate hog1 transcript levels in T. rubrum. As a means of preventing and treating dermatophytosis, our results contribute to the search for new potential drug therapies based on the molecular aspects of signaling pathways in T. rubrum.

Two different types of tandem sequences mediate the overexpression of TinCYP51B in azole-resistant Trichophyton indotineae

Trichophyton indotineae is an emerging dermatophyte that causes severe tinea corporis and tinea cruris. Numerous cases of terbinafine- and azole-recalcitrant T. indotineae-related dermatophytosis have been observed in India over the past decade, and cases are now being recorded worldwide. Whole genome sequencing of three azole-resistant strains revealed a variable number of repeats of a 2,404 base pair (bp) sequence encoding TinCYP51B in tandem specifically at the CYP51B locus position. However, many other resistant strains (itraconazole MIC ≥0.25 µg/mL; voriconazole MIC ≥0.25 µg/mL) did not contain such duplications. Whole-genome sequencing of three of these strains revealed a variable number of 7,374 bp tandem repeat blocks harboring TinCYP51B. Consequently, two types of T. indotineae azole-resistant strains were found to host TinCYP51B in tandem sequences (type I with 2,404 bp TinCYP51B blocks and type II with 7,374 bp TinCYP51B blocks). Using the CRISPR/Cas9 genome-editing tool, the copy number of TinCYP51B within the genome of types I and II strains was brought back to a single copy. The azole susceptibility of these modified strains was similar to that of strains without TinCYP51B duplication, showing that azole resistance in T. indotineae strains is mediated by one of two types of TinCYP51B amplification. Type II strains were prevalent among 32 resistant strains analyzed using a rapid and reliable PCR test.

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.

An update on the myriad antifungal resistance mechanisms in dermatophytes and the place of experimental and existential therapeutic agents for Trichophyton complex implicated in tinea corporis and cruris

INTRODUCTION

There is an epidemic emergence of increased resistance in dermatophytes with to antifungal drugs with ergosterol1 (Erg1) and Erg11 mutations to terbinafine and azoles. Apart from mutations, mechanisms that predict clinical failure include efflux pumps, cellular kinases, heat shock proteins (Hsp), and biofilms. Apart from itraconazole and SUBATM (Super-Bioavailable) itraconazole, measures that can be used in terbinafine failure include efflux-pump inhibitors, Hsp inhibitors and judicious use of antifungal drugs (topical + systemic) combinations.

AREAS COVERED

A PubMed search was done for the relevant studies and reviews published in the last 22 years using keywords dermatophytes OR Trichophyton, anti-fungal, resistance, mechanism and fungal AND resistance mechanisms. Our aim was to look for literature on prevalent species and we specifically researched studies on Trichophyton genus. We have analyzed varied antifungal drug mechanisms and detailed varied experimental and approved drugs to treat recalcitrant dermatophytosis.

EXPERT OPINION

Apart from administering drugs with low minimum inhibitory concentration, combinations of oral and topical antifungals (based on synergy data) and new formulations of existing drugs are useful in recalcitrant cases. There is a need for research into resistance mechanism of the existent Trichophyton strains in therapeutic failures in tinea corporis & cruris instead of data derived from laboratory strains which may not mirror clinical failures.

Treatment of recalcitrant cases of tinea corporis/cruris caused by T. mentagrophytes - interdigitale complex with mutations in ERG11 ERG 3, ERG4, MDR1 MFS genes & SQLE and their potential implications

BACKGROUND

Recalcitrant dermatophyte infections are being reported from various parts of the world due to varied causes including strain variation, steroid misuse, SQLE mutations, and variable quality of itraconazole pellet formulations. The oral drug preferred in endemic areas is itraconazole, to which MIC levels remain low, and clinical failures to itraconazole reported defy a sound scientific explanation.

OBJECTIVES

The objective of the study was to conduct a proteomic and genomic analysis on isolates from therapeutically recalcitrant case with isolation of gene mutations and enzymatic abnormalities to explain azole failures.

METHODS

Trichophyton mentagrophyte interdigitale complex strains were isolated from seven clinically non-responding tinea corporis/cruris patients, who had failed a sequential course of 6 weeks of terbinafine 250 mg QD and itraconazole 100 mg BID. After AFST 1 strain, KA01 with high MIC to most drugs was characterized using whole genome sequencing, comparative proteomic profiling, and total sterol quantification.

RESULTS

Sterol quantification showed that the standard strain of Trichophyton mentagrophytes (MTCC-7687) had half the ergosterol content than the resistant KA01 strain. Genomic analysis revealed mutations in SQLE, ERG4, ERG11, MDR1, MFS genes, and a novel ERG3 mutation. Proteomic analysis established the aberrant expression of acetyl Co-A transferase in the resistant strain and upregulation of thioredoxin reductase and peroxiredoxin.

CONCLUSION

Our findings demonstrate possible reasons for multidrug resistance in the prevalent strain with mutations in genes that predict terbinafine (SQLE) and azole actions (ERG4, ERG11, ERG3) apart from efflux pumps (MDR1, MFS) that can explain multidrug clinical failures.

Synergism between the Antidepressant Sertraline and Caspofungin as an Approach to Minimise the Virulence and Resistance in the Dermatophyte Trichophyton rubrum

Trichophyton rubrum is responsible for several superficial human mycoses. Novel strategies aimed at controlling this pathogen are being investigated. The objective of this study was to evaluate the antifungal activity of the antidepressant sertraline (SRT), either alone or in combination with caspofungin (CASP). We calculated the minimum inhibitory concentrations of SRT and CASP against T. rubrum. Interactions between SRT and CASP were evaluated using a broth microdilution chequerboard. We assessed the differential expression of T. rubrum cultivated in the presence of SRT or combinations of SRT and CASP. We used MTT and violet crystal assays to compare the effect of SRT alone on T. rubrum biofilms with that of the synergistic combination of SRT and CASP. A human nail infection assay was performed. SRT alone, or in combination with CASP, exhibited antifungal activity against T. rubrum. SRT targets genes involved in the biosyntheses of cell wall and ergosterol. Furthermore, the metabolic activity of the T. rubrum biofilm and its biomass were affected by SRT and the combination of SRT and CASP. SRT alone, or in combination, shows potential as an approach to minimise resistance and reduce virulence.

Gene Amplification of CYP51B: a New Mechanism of Resistance to Azole Compounds in Trichophyton indotineae

Trichophyton indotineae causes dermatophytosis that is resistant to terbinafine and azole compounds. The aim of this study was to determine the mechanisms of resistance to itraconazole (ITC) and voriconazole (VRC) in strains of T. indotineae. Two azole-sensitive strains (ITC MIC < 0.125 μg/mL; VRC MIC < 0.06 μg/mL) and four azole-resistant strains (ITC MIC ≥ 0.5 μg/mL; VRC MIC ≥ 0.5 μg/mL) were used for the investigation. The expression of MDR genes encoding multidrug transporters of the ABC family for which orthologs have been identified in Trichophyton rubrum and those of CYP51A and CYP51B encoding the targets of azole antifungal compounds were compared between susceptible and resistant strains. TinMDR3 and TinCYP51B were overexpressed in T. indotineae resistant strains. Only small differences in susceptibility were observed between TinMDR3 disruptants and parental strains overexpressing TinMDR3. Whole-genome sequencing of resistant strains revealed the creation of a variable number of TinCYP51B tandem repeats at the specific position of their genomes in three resistant strains. Downregulation of TinCYP51B by RNA interference (RNAi) restored the susceptibility of azole-resistant strains. In contrast, overexpression of TinCYP51B cDNA conferred resistance to a susceptible strain of T. indotineae. In conclusion, the reduced sensitivity of T. indotineae strains to azoles is mainly due to the overexpression of TinCYP51B resulting from additional copies of this gene.

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

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