Protein A (SpA) is a 42kDa virulence factor produced by Staphylococcus aureus, and is composed of five highly homologous consecutive extracellular Ig-binding domains, namely domains E, D, A, B, and C. This protein is present in both secreted and membrane-associated forms.
Protein A (SpA) causes B cells death in vitro, by binding to the Fc region of antibody and the Fab regions of the B-cell receptor, thus inhibiting its opsonophagocytosis. This protein is thought to be implicated in the evasion of host immune responses by Staphylococcus aureus, and thus, might be a candidate for vaccine development approaches to prevent severe S. aureus infections. S. aureus is responsible for nosocomial infections as well as a variety of human infections, such as food poisoning, toxic shock syndrome, endocarditis, septicemia, skin infections, soft tissue infections, and bone infections. It is also responsible for bovine and ovine mastitis. SpA typing or DNA sequence analysis of the variable repeat region of protein A gene is useful in determining S. aureus outbreak strains from those strains that are epidemiologically insignificant.
