Extensive dermatophytosis caused by terbinafine-resistant Trichophyton indotineae harboring Phe397Leu and Leu393Ser substitutions in the squalene epoxidase enzyme was diagnosed in France. Analysis of internal transcribed spacer sequences revealed the wide spread of this species in Asia and Europe. Detection of T. indotineae in animals suggests their possible role as reservoirs.

https://wwwnc.cdc.gov/eid/article/28/1/pdfs/21-0883.pdf

Extensive Dermatophytosis Caused by Terbinafine-Resistant Trichophyton indotineae, France

Background: During the past decade, a prolonged and serious outbreak of dermatophytosis due to a terbinafine-resistant novel species in the Trichophyton mentagrophytes / T. interdigitale complex is ongoing in India, and it spreads to several European countries.Objective: To investigate the molecular background of the squalene epoxidase (SQLE) gene in order to understand the risk of emergence and spread of multi-resistance in dermatophytes.Methods: Antifungal susceptibility for fluconazole, griseofulvin, itraconazole, ketoconazole, miconazole, naftifine, sertaconazole, and terbinafine was tested in 135 isolates from India, China, Australia, Germany and The Netherlands. Based on the latest taxonomic insights, strains were identified as three species: T. mentagrophytes s. str (n=35), T. indotineae (n=64 representing the Indian clone) and T. interdigitale s. str. (n=36).Results: High minimum inhibitory concentrations (MICs) of terbinafine (>16 mg/L) were found in 34 (53%) T. indotineae isolates. These isolates showed an amino acid substitution in the 397th position of the SQLE gene. Elevated MICs of terbinafine (0.5 mg/L) were noted in 2 (3%) T. indotineae isolates; these isolates lead to Phe415Val and Leu393Ser of the SQLE gene. Stability of the effect of the mutations was proven by serial transfer on drug-free medium. Substitutions of Lys276Asn and Leu419Phe were found in susceptible T. mentagrophytes strains. The double mutant Phe377Leu/Ala448Thr showed higher MIC values for triazoles.Conclusions: High MICs of terbinafine are as yet limited to T. indotineae, and are unlikely to be distributed through the T. mentagrophytes species complex by genetic exchange.

Antifungal Susceptibility and Mutations in the Squalene Epoxidase Gene in Dermatophytes of the Trichophyton mentagrophytes Species Complex.

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

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

Abstract 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. 

OUP accepted manuscript

One of the canonical features of the current outbreak of dermatophytosis in India is its unresponsiveness to treatment in majority of cases. Though there appears to be discordance between in vivo and in vitro resistance, demonstration of in vitro resistance of dermatophytes to antifungals by antifungal susceptibility testing is essential as it may help in appropriate management. The practical problem in the interpretation of antifungal susceptibility testing is the absence of clinical breakpoints and epidemiologic cutoff values. In their absence, evaluation of the upper limit of a minimal inhibitory concentration of wild type isolates may be beneficial for managing dermatophytosis and monitoring the emergence of isolates with reduced susceptibility. In the current scenario, most of the cases are unresponsive to standard dosages and duration of treatment recommended until now. This has resulted in many ex-cathedra modalities of treatment that are being pursued without any evidence. There is an urgent need to carry out methodical research to develop an evidence base to formulate a rational management approach in the current scenario.

The unprecedented epidemic-like scenario of dermatophytosis in India: III. Antifungal resistance and treatment options.

Dermatophytosis has gained interest in India due to rise in terbinafine resistance and difficulty in management of recalcitrant disease. The terbinafine resistance in dermatophytes is attributed to single nucleotide polymorphisms (SNPs) in squalene epoxidase (SE) gene. We evaluated the utility of amplified refractory mutation system polymerase chain reaction (ARMS PCR) for detection of previously reported point mutations, including a mutation C1191A in the SE gene in Trichophyton species. ARMS PCR was standardized using nine non-wild type isolates and two wild type isolates of Trichophyton species. Study included 214 patients with dermatophyte infection from March through December 2017. Antifungal susceptibility testing of isolated dermatophytes was performed according to CLSI-M38A2 guidelines. Among dermatophytes isolated in 68.2% (146/214) patients, Trichophyton species were predominant (66.4%). High (>2 mg/L, cut off) minimum inhibitory concentrations to terbinafine were noted in 15 (15.4%) Trichophyton mentagrophytes complex isolates. A complete agreement was noted between ARMS PCR assay and DNA sequencing. C to A transversion was responsible for amino acid substitution in 397th position of SE gene in terbinafine resistant isolates. Thus, the ARMS PCR assay is a simple and reliable method to detect terbinafine-resistant Trichophyton isolates.

/pdf/rapid-detection-of-terbinafine-resistance-in-trichophyton-4pf1w53eej.pdf

Rapid detection of terbinafine resistance in Trichophyton species by Amplified refractory mutation system-polymerase chain reaction.

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Rapid detection of terbinafine resistance in Trichophyton species by Amplified refractory mutation system-polymerase chain reaction.