The Staphylococcus aureus surface protein SasG and its homologues promote bacterial adherence to human desquamated nasal epithelial cells

Abstract

Staphylococcus aureusbinds to human desquamated nasal epithelial cells, a phenomenon likely to be important in nasal colonization. ClfB was identified previously as one staphylococcal adhesin that promoted binding to nasal epithelia. In this study, it is shown that theS. aureussurface protein SasG, identified previously byin silicoanalysis of genome sequences, and two homologous proteins, Pls ofS. aureusand AAP ofStaphylococcus epidermidis, also promote bacterial adherence to nasal epithelial cells. Conditions forin vitroexpression of SasG byS. aureuswere not found. Adherence assays were therefore performed withS. aureusandLactococcus lactisexpressing SasG from an expression plasmid. These studies showed that SasG did not bind several ligands typically bound byS. aureus. Significantly, SasG and Pls did promote bacterial adherence to nasal epithelial cells. Furthermore, pre-incubation of epithelial cells with purified recombinant proteins revealed that the N-terminal A regions of SasG, Pls and AAP, but not the B repeats of SasG, inhibited adherence ofL. lactisexpressing SasG in a dose-dependent fashion. These results suggest that SasG, Pls and AAP bind to the same as-yet-unidentified receptor on the surface of nasal epithelial cells. In addition, expression of SasG, like Pls, reduced adherence ofS. aureusto fibronectin and fibrinogen.