Functional characterisation of cell wall proteins that enhance nasal colonisation by Staphylococcus aureus, through binding to host mucin

Human nasal colonization with Staphylococcus aureus sets the stage for subsequent systemic infection. The mechanisms responsible for colonization are not fully understood. This study characterizes S. aureus adhesion to nasal mucosa in vitro and observes the interaction of S. aureus with mucin. S. aureus showed significantly higher binding to mucin during stationary phase in comparison to log-phase cells. Adherence of S. aureus srtA mutant to mucin was not significantly different from wild-type, thus Srt A shows no influence on S. aureus interaction with mucin. Adherence to mucin was saturable in a dose- and time-dependent fashion. Biotin–labelled mucin bound to surface protein (55 kDa) of cell wall extracted S. aureus which is encoded by the sbi gene. These data suggest that adherence factors are present on the surface of S. aureus such as sbi. Purified recombinant Sbi was prepared and the mucin binding capacity of the protein was tested by ELISA. In order to determine the function of specific domains of Sbi in adhesion, Sbi constructs with, without the IgG-domain and with B2-glycoprotein domain were expressed on the surface of E. coli BL21(DE3). The expression of Sbi with the B2-glycoprotein domain on the surface adhesion, emphasizing the role of Sbi in mucin adhesion. A profound binding effect was observed with Sbi incubated in wells coated with host mucin. Therefore, it is proposed to investigate a novel interaction of S. aureus to host mucin in order to control S. aureus nasal colonization.