Preparation and preclinical evaluation of two novel Staphylococcus aureus capsular polysaccharide 5 and 8-fusion protein (Hla-MntC-SACOL0723) immunoconjugates.

Staphylococcus aureus is one of the most common pathogens in the hospital and the community. The emergence of broad-spectrum antibiotic resistance in S. aureus has made the treatment process more difficult. Therefore, it is obvious that an effective prevention strategy against the pathogen could significantly reduce costs related to care in hospitals. In this report, we describe a simple approach to conjugate S. aureus capsular polysaccharide 5 (CP5) from S. aureus Reynolds strain and 8 (CP8) from S. aureus Becker strain to a fusion protein (Hla-MntC-SACOL0723) and investigation of its bioactivity. The conjugation was done by using ADH (as a bridge) and EDAC (as a coupling agent). The immunoconjugates were characterized by routine polysaccharide/protein contents assays followed by reverse phase chromatography and FTIR spectroscopy. The groups of mice were immunized with conjugate vaccines, capsular polysaccharides, and phosphate-buffered saline (PBS) as a control group. The functional activity of the vaccine candidates was evaluated by ELISA, opsonophagocytosis tests, and determination of bacterial load in challenge study. The results showed that the specific antibody (total IgG) titers raised against conjugate molecules were higher than those of the nonconjugated capsular polysaccharides. The opsonic activity of the conjugate vaccines antisera was significantly higher than polysaccharides alone (58% reduction in the number of bacteria versus 16.3% at 1:2 dilution, p < .05), Further, the conjugate vaccine group had a significant reduction in bacterial load after challenge with S. aureus COL strain cells as compared to the PBS and nonconjugated controls. In conclusion, the immunoconjugates could be developed as a potential vaccine candidate against S. aureus.

Identification of antigenic components of Staphylococcus epidermidis expressed during human infection.

A spectrum of in vivo-expressed Staphylococcus epidermidis antigens was identified by probing a bacteriophage lambda library of S. epidermidis genomic DNA with human serum from infected and uninfected individuals. This analysis resulted in identification of 53 antigen-encoding loci. Six antigenic polypeptides were expressed from these loci and purified. These polypeptides were the propeptide, mature amidase, and repeat sequence domains of the major autolysin AtlE, GehD (lipase), and two members of a conserved family of surface proteins (ScaA [AaE] and ScaB). AtlE, ScaA, and ScaB all exhibit human ligand binding capacity. Screening a bank of human serum samples revealed that there were significant increases in the amounts of reactive immunoglobulin G in infected individuals compared to the amounts in healthy individuals for the repeat sequence and mature amidase domains of AtlE, ScaB, and GehD. Vaccination of mice with recombinant antigens stimulated an immune response which in vitro opsonized S. epidermidis. In this study we identified prospective candidate antigens for prophylaxis or immunotherapy to control disease.