Type I collagen enhances biofilm formation of Staphylococcus epidermidis

The symbiotic skin bacterium Staphylococcus epidermidis moisturizes human skin, helps protect the body from external pathogens, and contributes to stimulation of the innate immune system. However, the relationship between the major skin protein collagen and S. epidermidis has not been studied extensively. Here, I observed development of S. epidermidis biofilms using scanning electron microscopy with an ionic liquid sample pretreatment technique; the biofilms were formed on a carbon-coated triacetylcellulose membrane in the presence or absence of collagen. In the presence of collagen, S. epidermidis cells adhered to the substrate, multiplied rapidly, secreted microvesicles, formed delicate web-like intercellular fibril connections, and became surrounded by an extracellular polymeric substance matrix. Remarkably, with extension of the cultivation time, cells on the surface of the thick biofilms aligned in a regular pattern; in areas with fewer bacterial cells on the biofilm surface, elongated thread-like structures formed between the cells. The firm attachment of S. epidermidis cells to the collagen substrate supports the presence of a previously proposed collagen-binding protein in this bacterium. The properties of the biofilms of S. epidermidis formed in the presence of collagen could reflect their lifestyle on vertebrate skin. The specific biofilm structure might be advantageous for moisturization of our skin, and important for understanding the role of S. epidermidis in our innate immune system and pathogenic processes of this bacterium.