Spectroscopic Characterization of Dermatophyte Pigments: Implications for Photodynamic Therapy

Abstract

The increasing resistance of dermatophytes to conventional antifungals has prompted the search for alternative therapeutic approaches, particularly antimicrobial photodynamic therapy (aPDT). The efficacy of aPDT depends on the spectral properties of endogenous photosensitizers, such as porphyrins and other pigments, which are influenced by the extraction solvent. This study investigated the collimated transmission spectra of extracts from clinically relevant dermatophytes—Trichophyton rubrum, T. mentagrophytes, and T. tonsurans—in acetone and hydrochloric acid (HCl) to characterize their pigment composition and photosensitizing potential.

The transmission spectra revealed distinct species-specific and solvent-dependent patterns. In acetone, all three species exhibited characteristic absorption maxima in the violet-blue region (400–450 nm), corresponding to porphyrin-like compounds (Soret band), with additional peaks in the visible range (500–650 nm, Q-bands) indicative of metalloporphyrins or other chromophores. Notably, T. rubrum extracts demonstrated the most pronounced absorption in this region, consistent with its higher sensitivity to 405 nm irradiation observed in functional studies.

Extraction with HCl significantly altered the spectral profiles, causing a bathochromic shift of the Soret band and enhanced absorption in the near-UV region. This effect is attributed to the protonation of porphyrin macrocycles and the release of metal ions from metalloporphyrins, which modifies their electronic structure and photophysical properties. The spectral differences between species were most evident in HCl extracts, suggesting that acidic conditions may facilitate the identification of species-specific pigment signatures.

These findings confirm that T. rubrum possesses a higher content of photosensitive pigments compared to T. mentagrophytes and T. tonsurans, correlating with its greater susceptibility to aPDT. The solvent-induced spectral changes highlight the importance of standardization in pigment extraction protocols for diagnostic and therapeutic applications. Furthermore, the species-specific spectral fingerprints provide a basis for developing optical diagnostic tools to differentiate dermatophyte species and predict their response to photodynamic treatment.

Speaker

Molchanova Ksenia Alexandrovna
Saratov Regional Clinical Dermatology and Venereology Dispensary, Ministry of Healthcare of the Saratov Region, Saratov, Russia
Russia

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