Recalcitrant dermatophyte infections: identification and risk factors

INTRODUCTION

Recalcitrant dermatophytosis is an emerging phenomenon that occurs worldwide, and Trichophyton indotineae is currently the prominent cause.

MATERIALS AND METHODS

Skin specimens from patients with tinea infection were obtained by scrubbing and then sectioned into three fragments. Two fragments were subjected to direct microscopic examination and culture, while the third portion was utilized in the PCR method.

RESULTS

Isolates were morphologically identified as Trichophyton mentagrophytes/interdigitale complex (n = 60 [83.33%]), Microsporum canis (n = 8 [11.11%]), Trichophyton rubrum (n = 3 [4.16%]), and Epidermophyton floccosum (n = 1 [1.38%]). Among 60 T. mentagrophytes complex isolates, 53 (88.33%) were classified as T. indotineae and seven as T. interdigitale genotype II. The disease duration was longer in the T. indotineae group (P = 0.035). Both Gradient PCR and skin-sampling methods yield similar results in terms of positive and negative cases (P = 1.0000). The time patients stopped their medication did not impact the positive case numbers (P = 0.803). Gender had no effects on the frequency (P = 0.699). Familial contamination, dermatologic disorder, and other underlying conditions did not differ in the two group infections (P > 0.05). Steroid usage is strongly associated with the emergence of tinea infection (P < 0.04). The duration of antifungal administration had a substantial effect on the emergence of resistant organisms (P = 0.05).

CONCLUSIONS

Steroid usage, T. indotineae involvement, and prolonged exposure to antifungals were the solid and influential factors in recalcitrant involvement. Regarding quick and suitable diagnosis and treatment, which is essential in preventing recalcitrant cases, we suggest that direct skin sample PCR can meet the demands.

Chinese expert consensus on management of antifungal-resistant dermatophytoses (2024 edition)

Antifungal-resistant dermatophytes (ARD) infection is a hotspot issue in clinical microbiology and the dermatology field. Trichophyton indotineae as the dominant species of dermatophyte with terbinafine-resistance or multidrug resistance, is easy to be missed detection clinically, which brings severe challenges to diagnosis and treatment. ARD infection cases have emerged in China, and it predicts a risk of transmission among human. Based on the existing medical evidence and research data, the Mycology Group of Combination of Traditional and Western Medicine Dermatology and Chinese Antifungal⁃Resistant Dermatophytoses Expert Consensus Group organized experts to make consensus on the management of the infection. Here, the consensus formulated diagnosis and treatment recommendations, to raise attention to dermatophytes drug resistance problem, and expect to provide reference information for the clinical diagnosis, treatment, prevention and control.

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.

Epidemiological study of antifungal-resistant dermatophytes isolated from Japanese patients

An epidemiological study of antifungal drug-resistant dermatophytes was conducted as a follow-up to our 2020 survey. Dermatophytes were isolated in 2022 from the same dermatology clinics as in the previous study. In total, 288 Trichophyton interdigitale and Trichophyton rubrum clinical isolates were obtained from 288 human cases of dermatophytosis in Tokyo, Saitama, Shizuoka, and Kumamoto, Japan. Four strains were found to be resistant to terbinafine (TRF) and susceptible to itraconazole (ITZ), luliconazole (LCZ), and ravuconazole (RVZ), and three other strains were found to be resistant to ITZ and susceptible to TRF, LCZ, and RVZ. We determined the sequences of the squalene epoxidase (SQLE)-encoding gene in the three TRF-resistant T. rubrum strains, and found that two strains harbored L393F missense mutations, and one strain harbored a F397L missense mutation. The results of the present study indicated that the prevalence of TRF-resistant dermatophytes has not increased since 2020. However, TRF-resistant T. interdigitale (L393F mutation) was isolated for the first time, indicating that attention should be paid to the presence of TRF-resistant T. interdigitale in the future. We also examined for the first time the epidemiology of ITZ-resistant T. rubrum in Japanese patients. Although the number of ITZ-resistant strains was not large, the results confirmed that ITZ-resistant T. rubrum strains do exist in Japanese patients.

Immunomodulatory responses of differentially polarized macrophages to fungal infections

Macrophages, the first line of defense against invasive fungi in the innate immune system, are widely distributed in the blood and tissues of the body. In response to various internal and external stimulators, macrophages can polarize into classically activated macrophages (M1) and alternatively activated macrophages (M2). These two types of polarized macrophages play different roles in antifungal activity and in maintaining the steady-state balance between inflammation and tissue repair. However, the antifungal mechanisms of M1- and M2-type macrophages have not been fully described. In this review, the immune regulatory mechanisms against pathogenic fungi of these two classical types of macrophages in various tissues are summarized. The effects of antifungal factors on macrophage differentiation are also highlighted. The description of these data, on the one hand provides valuable insight for future investigations and also highlights new strategies for the treatment of pathogenic fungal infections.

In vitro antifungal activity of heterocyclic organoboron compounds against Trichophyton mentagrophytes and Microsporum canis obtained from clinical isolates

The aim of this study was to investigate the in vitro activity of thirty-eight heterocyclic organoboron compounds (1a-o, 2a-j, 3a-m) against clinically isolated dermatophytes Trichophyton mentagrophytes and Microsporum canis. Minimum inhibitory concentrations (MICs) of compounds (1a-o, 2a-j, 3a-m) were determined according to published protocol Clinical and Laboratory Standards Institute (CLSI) M38-A2 broth microdilution method. The minimum fungicidal concentrations (MFCs) for both T. mentagrophytes and M. canis were found by subculturing each fungal suspension on potato dextrose agar. According to the results, heterocyclic organoboron compounds (1a-o, 2a-j, 3a-m) were found to be more effective against dermatophyte M. canis (MIC = 3.12-25 µg/ml) than T. mentagrophytes (MIC = 12.5-100 µg/ml). Our findings showed that 7-membered heterocyclic organoboron compounds (3a-m) (MIC = 12.5-50 µg/ml) have stronger in vitro antifungal activity against T. mentagrophytes than 5-membered heterocyclic organoboron compounds (1a-o, 2a-j) (MIC = 25-100 µg/ml). The MFC values for all compounds ranged from 6.25 to 200 µg/ml. The limited number of systemic antifungal agents used in the treatment of dermatophyte infections and the presence of side effects have led to the search for new treatment resources in recent years. Therefore, investigation of the effect of heterocyclic organoboron compounds against dermatophytes will be promising for the discovery of new antifungal compounds that have gained great importance today.

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.

A Paradigm Shift in the Treatment and Management of Onychomycosis

There is an increase in the incidence of onychomycosis, especially in at-risk populations. Onychomycosis is difficult to treat, as the efficacy of most antifungal agents is relatively low. Nondermatophyte molds (NDMs) and mixed infection (dermatophyte plus NDM) onychomycosis are contributing to growing antifungal resistance, as they are often underestimated and ignored due to incorrect diagnosis. There is a need for a paradigm shift in the management of onychomycosis to a patient-centered, holistic approach with an emphasis on laboratory diagnosis prior to initiating treatment, which enables the rational choice of the antifungal agent. Additionally, in the case of resistant infections, antifungal susceptibility testing is recommended. Strategies for effective management of onychomycosis include disinfection of fungal reservoirs in shoes and socks and prophylaxis posttreatment using topical antifungal agents. These measures may reduce the recurrence of onychomycosis and improve long-term clinical success.

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

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

Topical efinaconazole: A sequential combination therapy with oral terbinafine for refractory tinea unguium

Efinaconazole is a topical antifungal drug approved in Japan for tinea unguium. Although topical treatments generally have low cure rates with a prolonged therapy period, a Cochrane review confirmed that high‐quality evidence supports the effectiveness of efinaconazole for the complete cure of tinea unguium. Combination therapy is a way to improve the cure rate of onychomycosis. In this study, topical efinaconazole was administrated to 12 patients who had been treated with oral terbinafine (125 mg daily) for more than 20 weeks with little expected effect. Because terbinafine accumulates for a long time in the nail, treatment immediately followed by other drugs can be considered sequential combination therapy. During terbinafine monotherapy, the percentage involvement decreased from 53.5% to 44.0% after 37.4 weeks and the effective and cure rates were 16.7% and 0%, respectively. During sequential topical efinaconazole therapy combined with lasting terbinafine in the nail, the percentage involvement decreased from 44.0% to 18.7% after 28.4 weeks, and the effective and cure rates were 66.7% and 16.7%, respectively. The improvement rate per month of combination therapy (12.6%) was higher than that with monotherapy (2.1%) (p = 0.002). There were no serious side‐effects. This sequential combination therapy with efinaconazole was effective in poor terbinafine responders, making it a promising regimen for improving the cure rate of tinea unguium.

Treatment Outcome with Fosravuconazole for Onychomycosis

Fosravuconazole L-lysine ethanolate (F-RVCZ), a ravuconazole prodrug, is a newly available agent with high expectations for efficacy in the treatment of onychomycosis. However, clinical data regarding the efficacy of F-RVCZ are limited because the drug was launched only in Japan in 2018. Therefore, we analyzed the outcome of F-RVCZ therapy in the treatment of onychomycosis at outpatient dermatology clinics in Japan. We examined data for 109 patients (68 male, 41 female) with varying clinical type, including total dystrophic onychomycosis and dermatophytoma, and a wide range of age groups, including the elderly. The complete cure rate at 12 weeks was 6.4% (7/109) and 67.9% (74/109) at the last visit (mean time to last visit: 32 ± 14.2 weeks). Mean rate of improvement in the affected nail area was 49.1 ± 23.3% at 12 weeks and 86.8 ± 22.4% at the last visit. Efficacy at 12 weeks and the last visit, respectively, was as follows: none, 4 cases and 1 case; slight, 35 cases and 4 cases; moderate, 51 cases and 21 cases; significant, 12 cases and 9 cases; complete cure, 7 cases and 74 cases. There were no serious adverse events. This retrospective survey was the first large-scale analysis of actual clinical practice outcomes and had minimal exclusions. Compared to previous reports, our results demonstrated excellent efficacy of F-RVCZ therapy in a variety of patients. Considering our results and the ease of oral administration (1 capsule/day for 12 weeks) and few adverse events, F-RVCZ therapy appears to be a useful option for the treatment of onychomycosis.

In Vitro activity of ravuconazole against Candida auris and vaginal candida isolates

BACKGROUND

Ravuconazole is an extended-spectrum triazole agent that is efficient in vitro against Candida spp. and has been approved to work as an oral formulae for onychomycosis in Japan in 2018. However, nobody had determined the MIC of ravuconazole against the Candida auris, which is known as an emerging multidrug-resistant yeast. Meanwhile, rare is known of the in vitro activity of ravuconazole against vaginal Candida isolates.

OBJECTIVES

To investigate the activity of ravuconazole against C. auris and vaginal Candida isolates of China and assess the feasibility of ravuconazole in the treatment of candidiasis caused by C. auris and other Candida spp.

METHODS

We determined the in vitro activity of ravuconazole and 9 comparators against 15 C. auris isolates and determined the MIC of ravuconazole on 525 vaginal Candida isolates (Candida albicans, Candida tropicalis, Candida glabrata and Candida parapsilosis) from 9 provinces of China by Clinical and Laboratory Standards Institute (CLSI) methodology.

RESULTS

The MICs of fluconazole and amphotericin B on C. auris were much higher than second-generation azoles and echinocandins. Ravuconazole was active against all the C. auris isolates and as effective as isavuconazole, posaconazole and echinocandins while showed a better antifungal activity than itraconazole, voriconazole to C. auris. For vaginal Candida isolates, the proportion of ravuconazole-resistant isolates is 0.19% (1/525).

CONCLUSIONS

Ravuconazole was in good active against C. auris and vaginal Candida isolates, which suggested ravuconazole could be used in the treatment of drug-resistant candidiasis.

Epidemiological study of terbinafine-resistant dermatophytes isolated from Japanese patients

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

Rapid Molecular Detection of Terbinafine-resistant Dermatophytes

Terbinafine (TRF)-resistant Trichophyton interdigitale and Trichophyton rubrum have been isolated from human patients. These strains have missense mutations (Leu393Ser/Phe or Phe397Leu) in the squalene epoxidase-encoding gene, SQLE. We developed a PCR detection method to identify hotspot mutation sites in SQLE genes of dermatophytes. To sequence hotspots in isolates, we prepared primers based on conserved sequences of T. rubrum and T. interdigitale SQLEs. Approximately 390-bp long DNA bands for T. rubrum, T. interdigitale, and Trichophyton indotineae strains were sequenced. Hotspots were detected only in TRF-resistant strains. This PCR-based method is simpler and more rapid than the conventional test.