Aberrations in Expression of the β Antigen of Streptococcus agalactiae

GBS of defined capsular antigen types can be subtyped on the basis of the strain-variable and surface-anchored c proteins cα and cβ, and R proteins. These proteins may function as virulence factors and they are targets of protective antibodies. Of the c proteins, cβ occurred in 24% of GBS as found by using a monoclonal antibody (MAb)-based fluorescent antibody test (FAT; 3). cβ also has the ability to bind to the Fc region of human IgA by virtue of two domains, A and B (2). In addition to A and B, this protein has one cell wall-spanning (W) and one membrane-spanning domain M (2). In the present study, we have compared cβ protein detection by the FAT with detection of the β gene by PCR amplification (β-PCR).