Identification of conserved antigens from staphylococcal and streptococcal pathogens

The design of vaccines containing epitopes shared between different human pathogens may lead to cross-species protection. In order to identify potentially conserved bacterial antigens, bacteriophage expression libraries of genomic DNA from Streptococcus agalactiae, Streptococcus pneumoniae and Streptococcus pyogenes were probed with human sera from Staphylococcus aureus-infected and healthy individuals. By comparison with previous screening data from Staphylococcus epidermidis and Staph. aureus, putative antigenic, conserved domains across the genera were identified. In particular, three potentially antigenic conserved regions were identified based on the N-terminal domain of SACOL0609 (SdrD), the C-terminal domain of SACOL0723 (ScaB) and the C-terminus of SACOL1140 (IsdA) from Staph. aureus. The three domains were overexpressed, recombinant proteins were purified and polyclonal antisera raised against them recognized cell surface-located proteins from both staphylococcal and streptococcal species. The antisera were also able to opsonize both Staph. aureus and Strep. agalactiae thereby increasing their phagocytic uptake by human neutrophils. The conserved antigenic domains therefore represent potential cross-protective vaccine candidates.