[Dermatophytes do not produce sialidase in vitro]

Sialidase (EC 3.2.1.18) is a pathogenicity factor of many microorganisms, and may also play a role in adhesion of dermatophytes to the epithelia of their hosts by the hydrolytical cleavage of terminal, negatively charged sialic acids of glycoconjugates on the cell surfaces, thus allowing fungal lectins to bind to the subterminal sugars. Therefore, 116 strains of seven species of dermatophytes were investigated for sialidase production. Two highly sensitive, quantitative sialidase assays were applied to cell homogenates and culture supernatants from seven different media of the fungi, but were always negative for sialidase activity. However, sialidase activity was always detected in Ophiostoma stenoceras used as a positive control cultivated in parallel; the enzyme was inducible by sialylated mucins. A sialidase-dependent pathomechanism for dermatophytes appears unlikely based on the results presented.