Immunogenic compositions and methods for eliciting an immune response against S. epidermidis and other related staphylococci are provided. The immunogenic compositions can include immunogenic conjugates of poly-γ-glutamic acid (such as γDLPGA) polypeptides of S. epidermidis, or related staphylococci that express a γPGA polypeptide. The γPGA conjugates elicit an effective immune response against S. epidermidis, or other staphylococci, in subjects to which the conjugates are administered. A method of treating an infection caused by a Staphylococcus organism that expresses cap genes is also disclosed. The method can include selecting a subject who is at risk of or has been diagonosed with the infection by the Staphylococcus organism which expresses γPGA from the cap genes. Further, the expression of a γPGA polypeptide by the organism can then be altered.