Provided is a P4 peptide, which contains functional epitopes of the PsaA protein of Streptococcus pneumoniae, and related methods and compositions. P4 peptide mimetics having a conformational structure identical or similar to the conformation of P4 (e.g., SEQ ID NO: 1 and SEQ ID NO:2) are provided. An antibody that specifically binds to the epitope defined by the disclosed peptides is provided. A P4-specific antibody is PsaA-specific since P4 defines an epitope specific for PsaA. Immunogenic compositions comprising the peptide of SEQ ID NO: 1 and a pharmaceutical carrier or the peptide of SEQ ID NO:2 and a pharmaceutical carrier are also provided. Methods of using the peptides and antibodies of the invention are provided.