Interference of Malassezia restricta in the invasion of Staphylococcus aureus into human keratinocytes.

The human skin is a crucial defense system, protecting against external stressors. However, the skin also hosts various microorganisms that impact skin health and disease. Therefore, the polymicrobial interaction in the skin is particularly interesting since it can significantly influence alterations in the virulence traits of microbes and the immune responses of the hosts. This study aimed to investigate the influence of Malassezia restricta, a predominant fungal species on human skin, on the virulence of Staphylococcus aureus, a prominent skin bacterium associated with atopic dermatitis. Our findings revealed that M. restricta effectively interferes with the invasion of S. aureus into human keratinocytes, suggesting a potential mechanism for influencing bacterial infection by the fungus. Additionally, we observed that M. restricta exhibits fibronectin binding capabilities, a key mediator in the S. aureus invasion of keratinocytes. Physicochemical analysis indicated the involvement of a heat-unstable component, likely a M. restricta cell surface protein, which necessitates physical contact between the fungus and keratinocytes for fibronectin binding. Collectively, our results suggest the influential role of M. restricta in the pathogenesis of S. aureus and reveal a novel aspect of this fungal species within the human skin microbial community.