Purification of type 5 capsular polysaccharide from Straphylococcus aureus by a simple efficient method

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.

Prevalence of capsular polysaccharide (CP) types of Staphylococcus aureus isolated from bovine mastitic milk and protection of S. aureus infection in mice with CP vaccine

To determine the prevalence of capsular polysaccharide (CP) types of Staphylococcus aureus isolated from bovine mastitic milk in Korea, the protective effect of the conjugates, composed of microencapsulated S. aureus clinical isolate type 8 CP bound to Pseudomonas aeruginosa exotoxin A (ETA) was evaluated in mice. Of 107 S. aureus isolates, serotype 5 and 8 accounted for only 26 or 24.2%. When serotype 336 antiserum was employed, fifty of the remaining 81 isolates were typed as 336, 26 reacted with two serotypes, and 5 were nontypeable. Mice challenged with the same strain used for immunization had fewer S. aureus cells in their kidneys than mice challenged with the heterologous strain. But the magnitudes of difference on bacterial clearance were similar in both groups, indicating that the significance of this result remains to be determined. Mice immunized with the conjugate elicited an antibody response 3 days post injection, which persisted for 13 days of the observation period after second injection in some mice. The mice immunized with the CP8-ETA conjugates developed antibodies significantly higher than those immunized with CP-Freund's adjuvant or PBS. In in vivo bacterial challenge experiment, the survival rate of mice immunized with CPS-ETA conjugate was significantly higher than that of mice immunized with PBS. It was suggested that CP8-ETA vaccine had a potential to protect mice against experimental S. aureus bacteremia.

Immune recruitment and bactericidal activity of neutrophils in milk of cows vaccinated with staphylococcal alpha-toxin

The ability of Staphylococcus aureus alpha-toxin to recruit neutrophils in the milk of vaccinated cows and the bactericidal efficiency of these neutrophils were evaluated. Six lactating Holstein cows that were free of intramammary infection received systemic immunization by subcutaneous injection of Freund's incomplete adjuvant with alpha-toxin (n = 2), alpha-toxin mixed with type 5 capsular polysaccharide (n = 2), or a conjugate of these two antigens (n = 2). Controls (n = 4) and vaccinated cows (n = 6) received intramammary infusions of alpha-toxin. No increase in somatic cell count was recorded in quarter milk samples from unimmunized cows; however, 10 micrograms of alpha-toxin induced a local inflammatory reaction in vaccinated cows that was characterized by early and massive cellular recruitment into the mammary gland. More than 90% of the recruited cells were neutrophils. The speed and magnitude of the cellular recruitment were dose-dependent; the threshold dose was 0.6 microgram. Milk samples showed significant bactericidal activity against the type 5 S. aureus strain, regardless of the vaccine used, and showed a decrease in bacterial count of about 2 log10 from the initial inoculum. The best efficiency was recorded during the early phase of cellular recruitment with concomitant activation of blood-derived neutrophils. This study demonstrates that a bacterial virulence factor, alpha-toxin, is able to induce immune recruitment of neutrophils for efficient bactericidal activity in milk when cows are immunized with alpha-toxin that is used either as a nonconjugate vaccinate or as a carrier protein in a conjugate vaccine. The study also suggests that neutrophils that are recruited from blood are activated during inflammation in response to specific antigens.

Capsular polysaccharide types 5 and 8 of Staphylococcus aureus bind specifically to human epithelial (KB) cells, endothelial cells, and monocytes and induce release of cytokines

In order to examine the possible implication of capsular polysaccharide (CP) types 5 and 8 (CP5 and CP8) from Staphylococcus aureus in the pathological mechanism associated with staphylococcal infections, we tested the immunomodulatory effects of CP5 and CP8 on human epithelial KB cells, endothelial cells, and monocytes. Using biotinylated CP5 and CP8, we provide evidence that both CPs bind to KB cells, endothelial cells, and monocytes in a dose- and calcium-dependent manner through specific interactions. These results were confirmed by competition experiments using soluble cell extracts. Furthermore, we show that CPs bind to identical cell membrane receptors on all three types of human cells and that human normal serum contains a factor(s) which inhibits the binding of both CPs to human KB cells, endothelial cells, and monocytes. The ability of CP5 and CP8 to stimulate the production of cytokines by the human cells was then examined. CP5 and CP8 trigger KB cells to produce interleukin-8 (IL-8); endothelial cells to produce IL-8 and IL-6; and monocytes to produce IL-8, IL-6, IL-1 beta, and tumor necrosis factor alpha. The release of cytokines by all three types of cells is time dependent and dose dependent, and the tumor necrosis factor alpha production by monocytes is not affected by the addition of polymyxin B. We further confirm that human normal serum inhibits the immunomodulatory effects of both polysaccharides on each kind of cell. These results confirm that S. aureus CPs act as bacterial adhesins having immunomodulatory effects for human cells.