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Utility of MALDI-ToF MS for Recognition and Antifungal Susceptibility of Nannizzia, an Underestimated Group of Dermatophytes

Summary

Nannizzia species are soil-dwelling fungi that increasingly cause stubborn skin, nail, and hair infections in humans and animals. This study tested two laboratory methods for identifying these fungi and measured their sensitivity to eight antifungal drugs. The faster liquid-based method was slightly more accurate (67%) than the traditional culture method (62%), though neither method could identify six very rare species. Terbinafine emerged as the most effective antifungal treatment in laboratory tests.

Background

Nannizzia species are geophilic dermatophytes increasingly implicated in stubborn skin, hair, and nail infections. However, MALDI-TOF MS evaluations and antifungal-susceptibility data have focused almost exclusively on N. gypsea, with limited biochemical profiles and MIC cut-offs available for the genus.

Objective

To benchmark two commercial MALDI-TOF MS libraries (MSI-2 and Bruker MALDI Biotyper Filamentous-Fungi Library 6.0/2023) for identification of Nannizzia species and determine in vitro activity of eight antifungals against a genus-wide panel of Nannizzia species.

Results

MSI-2 achieved 62% accuracy with 7-day PDA cultures, while Biotyper yielded 67% within four days. Combined low-confidence scores increased overall accuracy to 73%. MSI-2 excelled for N. gypsea (73%) and uniquely detected N. nana (50%). Terbinafine showed the lowest geometric mean MIC (0.009 mg/L), while fluconazole exhibited the highest values.

Conclusion

Diagnostic coverage of Nannizzia remains incomplete with six rare species unrecognized by either database. Expanding commercial MALDI-TOF MS libraries with spectra from rare species and performing routine susceptibility testing are essential to optimize patient management and develop targeted treatment protocols.
  • Published in:Mycoses,
  • Study Type:Experimental Study,
  • Source: PMID: 40965921, DOI: 10.1111/myc.70117
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