A novel peptide isolated from phage library to substitute a complex system for a vaccine against staphylococci infection.

Staphylococcus aureus is a major human pathogen and many of the strains are resistant to conventional antibacterial treatment. The bacteria cause disease largely due to the production of multiple toxins, whose synthesis is controlled by an RNA molecule termed RNAIII. The production of RNAIII is induced by quorum sensing systems, one of them containing the protein RNAIII activating protein (RAP). Here we show that we partially purified supernatant of S. aureus, used this fraction to vaccinate mice, and selected antibody-binding peptides by phage display. Mice were vaccinated with the various peptides and challenged with S. aureus. One of the binding peptide termed R13 induced a protective immune response. Western blot analysis showed that the anti-R13 antibodies specifically bind to native or recombinant RAP. Mice vaccinated with R13 were protected and protection was sustained for the duration of the 6-month study period. Our results show that R13 could be used as a long-term effective protective-peptide-vaccine to prevent S. aureus infections and once again show that targeting the RAP quorum sensing system is an effective approach to preventing staphylococcal infections. In addition our studies show that selection of specific protective peptides by phage display using sera induced by complex antigens is a rapid and effective way to identify the protective antigen and select for a peptide vaccine.