The major 20-kDa polysaccharide of Staphylococcus epidermidis extracellular slime and its antibodies as powerful agents for detecting antibodies in blood serum and differentiating among slime-positive and -negative S. epidermidis and other staphylococci species.

Staphylococcus epidermidis has been recognized as an important pathogen in immunocompromised hosts and patients with prosthetic or implanted medical devices. A highly adhesive extracellular material (slime or biofilm) produced by certain strains is associated with bacterial adherence to and growth on biomaterials contributing to pathogenesis of bacteremia. We have recently reported on the isolation and characterization of a sulfated 20-kDa acidic polysaccharide which constitutes slime's major component. Immunization of rabbits with crude slime and 20-kDa polysaccharide gave rise to readily reactive sera without manipulation of the 20-kDa polysaccharide structure. Immunological studies using purified polyclonal antibodies to 20-kDa polysaccharide by direct and competitive ELISA showed that they exhibit a high degree of reactivity and specificity with the homologous antigen. A significant proportion of the reactivity of antibodies to crude slime was also shown to be attributed to the 20-kDa polysaccharide. This polysaccharide is immunogenic in humans since blood sera derived from patients 10-15 days after confirmation of slime-producing S. epidermidis bacteremia gave approximately 16 times higher reactivity than that of healthy individuals. Antibodies to 20-kDa polysaccharide were able to recognize and react specifically with slime-positive S. epidermidis strains compared to slime-negative ones (2 to 5 times higher reactivity). Moreover, these antibodies exhibited statistically significant (P < 0.05) differences in the degree of reactivity among S. epidermidis and other staphylococci species. These results open a new area in the diagnosis of S. epidermidis infection by direct analysis in blood sera, in differentiating among slime-positive and slime-negative strains as well as in distinguishing slime-producing S. epidermidis from other staphylococci species by simple laboratory tests.