In vitro activity of azole derivatives and griseofulvin against planktonic and biofilm growth of clinical isolates of dermatophytes.

As shown by recent research, most of the clinically relevant fungi, including dermatophytes, form biofilms in vitro and in vivo, which may exhibit antimicrobial tolerance that favour recurrent infections. The aim of this study was to determine the minimum inhibitory concentrations (MICs) of itraconazole (ITC), voriconazole (VCZ) and griseofulvin (GRI) against Trichophyton rubrum, Trichophyton tonsurans, Trichophyton mentagrophytes, Microsporum canis and Microsporum gypseum in planktonic and biofilm growth. For the planktonic form, susceptibility testing was performed according to the Clinical and Laboratory Standards Institute (CLSI), document M38-A2, while biofilm susceptibility was evaluated using the XTT colorimetric essay. The planktonic growth of all strains was inhibited, with MIC values ranging from 0.00195 to 0.1225 µg/mL for VRC, 0.00195 to 0.25 µg/mL for ITC and <0.0039 to 4 µg/mL for GRI, while a 50-fold increase in the MIC was required to significantly reduce the metabolic activity (P < .05) of dermatophyte biofilms. In brief, the ability of dermatophytes to form biofilms may be a contributing factor for the recalcitrance of dermatophytoses or the dissemination of the disease.

Quantitative and structural analyses of the in vitro and ex vivo biofilm-forming ability of dermatophytes.

PURPOSE: The aim of this study was to evaluate the in vitro and ex vivo biofilm-forming ability of dermatophytes on a nail fragment. METHODOLOGY: Initially, four isolates of Trichophyton rubrum, six of Trichophyton tonsurans, three of Trichophyton mentagrophytes, ten of Microsporum canis and three of Microsporum gypseum were tested for production biomass by crystal violet assay. Then, one strain per species presenting the best biofilm production was chosen for further studies by optical microscopy (Congo red staining), confocal laser scanning (LIVE/DEAD staining) and scanning electron (secondary electron) microscopy. RESULTS: Biomass quantification by crystal violet assay, optical microscope images of Congo red staining, confocal microscope and scanning electron microscope images revealed that all species studied are able to form biofilms both in vitro and ex vivo, with variable density and architecture. M. gypseum, T. rubrum and T. tonsurans produced robust biofilms, with abundant matrix and biomass, while M. canis produced the weakest biofilms compared to other species. CONCLUSION: This study sheds light on biofilms of different dermatophyte species, which will contribute to a better understanding of the pathophysiology of dermatophytosis. Further studies of this type are necessary to investigate the processes involved in the formation and composition of dermatophyte biofilms.