Sialic acids are absent from the dermatophytes Trichophyton mentagrophytes and Trichophyton rubrum

Experiments were performed to determine whether sialic acids are expressed in two dermatophytes: Trichophyton rubrum and T. mentagrophytes, similarly to other fungal pathogens. Chemical extraction of mycelia and microconidia followed by high-performance thin-layer chromatography and colorimetric assays were all negative for sialic acid. Incubation of dermatophytes in the presence of Limax flavus agglutinin, specific for sialic acid, was negative in a fluorescence staining test. We have also used other lectins that bind to sialic acid and/or other sugar residues, and these ligands coupled to fluorescein strongly stained these fungi. Such fluorescence staining was not abolished or reduced when fungi were pretreated with sialidase. Different strains of influenza virus which recognize sialic acid residues were also used, but no agglutination of the dermatophytes was observed. Based on these methods, which successfully revealed the presence of sialic acids in other fungal pathogens, we show that these monosaccharides do not occur in both dermatophyte species. Thus, sialic acids do not seem to play a role in the pathogenicity of these fungi.