The invention relates to compositions of the capsular polysaccharide/adhesin (PS/A) of staphylococci. The PS/A may be isolated or synthesized and includes various modifications to the structure of native PS/A based on the chemical characterization of PS/A. The invention also relates to the use of the PS/A as a vaccine for inducing active immunity to infections caused by Staphylococcus aureus, S. epidermidis, other related coagulase-negative staphylococci and organisms carrying the ica (intracellular adhesin) locus, and to the use of antibodies directed to PS/A for inducing passive immunity to the same class of infections.