FRET-based molecular diagnostics for rapid and specific dermatophyte detection and differentiation.

Background

Dermatophytosis, a common superficial fungal infection in companion animals, is caused primarily by Microsporum canis, Nannizzia gypsea, and Trichophyton mentagrophytes. These infections are highly contagious and possess significant zoonotic potential, impacting both animal health and public well-being. Therefore, rapid and accurate species-level identification is critically needed for effective treatment, precise transmission control, and robust epidemiological surveillance, given the differing clinical implications and transmission routes of each dermatophyte.

Current diagnostic approaches, such as microscopy and fungal culture, suffer from substantial drawbacks. Fungal culture, while traditional, is notoriously slow, often requiring two to four weeks for definitive results. Moreover, it can be inconclusive due to phenotypic similarities among species and susceptibility to environmental contamination. While molecular methods like real-time PCR offer speed, existing dye-based assays frequently exhibit reduced sensitivity at low DNA concentrations, non-specific amplification, and cross-reactivity with non-target fungi, hindering reliable species differentiation.

Technology

This real-time PCR assay employs Fluorescence Resonance Energy Transfer (FRET) for the simultaneous detection and differentiation of Microsporum canis, Nannizzia gypsea, and Trichophyton mentagrophytes. It targets a ~200 base pair region of the chitin synthase 1 (CHS1) gene using a single primer set and dual probes: a 6-FAM-labeled anchor and an LC Red 640-labeled reporter. Species differentiation is achieved through specific polymorphisms in the reporter probe region, yielding distinct melting temperature (Tm) profiles for each dermatophyte, such as T. mentagrophytes at ~51.8°C and M. canis at ~56.1°C. This method offers sensitive detection down to a single gene copy and high specificity.

This technology is highly differentiated from traditional fungal culture, which is slow (weeks) and often inconclusive. Unlike other molecular methods like SYBR Green or EvaGreen assays, this FRET-based approach provides superior sensitivity and specificity, avoiding non-specific amplification and cross-reactivity with non-target fungi. Its dual-probe design combined with high-resolution melting analysis ensures reliable species discrimination. The short amplicon size enhances amplification efficiency and robustness against DNA degradation or PCR inhibitors, making it ideal for clinical samples. This rapid, accurate species-level identification is crucial for timely treatment, effective transmission control, and epidemiological surveillance of dermatophytosis.

Benefits

• Rapid diagnosis, providing results in approximately 2.5 hours.
• Simultaneous detection and accurate species differentiation of *Microsporum canis*, *Nannizzia gypsea*, and *Trichophyton mentagrophytes*.
• High sensitivity, detecting as low as a single gene copy.
• High specificity, avoiding cross-reactivity with non-target fungi.
• Enables improved clinical management, targeted treatment, and infection control due to precise species identification.
• Robustness for clinical samples, tolerating degraded DNA and PCR inhibitors.

Applications

• Veterinary dermatophyte diagnostic testing
• Animal dermatophyte screening programs
• Zoonotic disease surveillance
• Guide veterinary treatment decisions
• Dermatophyte research and epidemiology

Additional info

This real-time PCR assay utilizes Fluorescence Resonance Energy Transfer (FRET) with dual probes to simultaneously detect and differentiate *Microsporum canis*, *Nannizzia gypsea*, and *Trichophyton mentagrophytes*. It targets a ~200 bp chitin synthase 1 (CHS1) gene region. Species differentiation relies on specific polymorphisms within the reporter probe binding site, yielding distinct melting temperature profiles for sensitive, specific identification down to a single gene copy.