Subtilisin Sub3 is involved in adherence of Microsporum canis to human and animal epidermis

The aim of this study was to assess the role of the secreted keratinolytic subtilisin-like protease Sub3 in adherence of Microsporum canis to epidermis from various susceptible species, in addition to cat for which this role was recently demonstrated. Firstly, we showed by immunostaining that Sub3 is not expressed in arthroconidia from an M. canis SUB3 RNA-silenced strain but is present on the surface of arthroconidia from a SUB3 non-silenced parental strain. Secondly, comparative adherence assays using arthroconidia from both M. canis strains and skin explants from humans, dogs, horses, rabbits, guinea pigs, mice and cats revealed that only 8-16% of arthroconidia from the SUB3 silenced strain adhered to different types of epidermis when compared to the control strain. Attempts to restore fungal adherence by the addition of recombinant Sub3 failed in the tested conditions. Overall results show for the first time that Sub3 is necessary for the adherence of M. canis arthroconidia to epidermis from humans and other animal species than cat, supporting the idea that Sub3 plays a central role in colonization of keratinized host structures by M. canis, whatever the host.