The role of capsular antigens in Staphylococcus aureus immunity

Most clinical blood isolates of Staphylococcus aureus have been shown to be encapsulated. Techniques are now available for the preparation of type-specific capsular antisera and to provide reliable serologic methods for the identification of clinical isolates of Staphylococcus aureus. Epidemiologic studies in the U.S.A. and Europe indicated the prevalence of capsular types 5 and 8 among clinical isolates from human, bovine, and poultry. Encapsulated types 5 and 8 resisted in vitro phagocytosis and specific anti-capsular serum facilitated type-specific opsonization of S. aureus by polymorphonuclear leukocytes (PMN). The structure of the prevalent types 5 and 8 capsular polysaccharides (CP) have been elucidated. Vaccines of CP conjugated to exotoxin A of Pseudomonas aeruginosa have been prepared and have been injected into animals and human volunteers. Antibodies elicated by these conjugates facilitated opsonization of specific S. aureus types by human PMN.