Temperature- and Contact Time-Dependent Efficacy of Common Disinfectants Against Selected Trichophyton, Microsporum, and Nannizzia Strains

Dermatophytosis requires environmental decontamination because dermatophyte spores can persist on contaminated surfaces for prolonged periods. However, regulatory frameworks in several countries rely solely on Trichophyton mentagrophytes to evaluate disinfectant efficacy, which may not represent the diversity of dermatophytes encountered in veterinary settings. In this study, we aimed to evaluate the disinfectant efficacy of four commercial disinfectants [quaternary ammonium compounds (QACs), potassium peroxymonosulfate (KMPS), iodine, and sodium dichloroisocyanurate (NaDCC)] against T. mentagrophytes, Trichophyton verrucosum, Microsporum canis, and Nannizzia gypsea at 25 °C and 4 °C. Minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) were determined using broth dilution methods with a 30-min contact time; a time-kill assay was performed at the MFC of each disinfectant to assess fungicidal activity over 30 min. MICs were 125–64,000 ppm, with QACs showing the greatest variability among strains (32-fold). KMPS consistently showed an MFC/MIC ratio of 1 across all strains and temperatures, whereas QACs reached a ratio of 8 against T. mentagrophytes at 25 °C suggesting fungistatic activity. In the time-kill assay, all disinfectants achieved a ≥ 3-log10 reduction within 30 min, except QACs against T. mentagrophytes at 25 °C (2.85-log10). At 25 min, fewer samples reached this threshold at 4 °C than at 25 °C (16.7% vs. 43.8%, p = 0.007), but this difference was not observed at 30 min (p = 0.111). NaDCC showed the strongest temperature dependence. These preliminary findings indicate that the inclusion of additional dermatophyte species and low-temperature conditions in standardized disinfectant efficacy testing warrants further evaluation using multiple isolates.