A STAPHYLOCOCCUS-AUREUS CAPSULAR POLYSACCHARIDE (CP) VACCINE AND CP-SPECIFIC ANTIBODIES PROTECT MICE AGAINST BACTERIAL CHALLENGE

The efficacy of capsular polysaccharide (CP)-specific antibodies elici ted by active immunization with vaccines composed of Staphylococcus au reus types 5 and 8 CP linked to Pseudomonas aeruginosa exoprotein A or with immune immunoglobulin G (I-IgG) obtained from vaccinated plasma donors was tested in lethal and sublethal bacterial mouse challenge mo dels. A dose of 2 x 10(5) CFU of S. aureus type 5 CP per mouse adminis tered intraperitoneally (i.p.) with 5% hog mucin was found to cause 80 to 100% mortality in BALB/c mice within 2 to 5 days. Mice passively i mmunized i.p. 24 h earlier or subcutaneously 48 h earlier with 0.5 ml of I-IgG showed significantly higher average survival rates than anima ls receiving standard IgG or saline (P < 0.01) following the bacterial challenge. Animals actively immunized with the monovalent type 5 CP-P . aeruginosa exoprotein A conjugate showed a survival rate of 73% comp ared with 13% in phosphate-buffered saline-immunized animals. The prec hallenge geometric mean titer of type 5 CP antibodies in animals that died was significantly (P < 0.05) lower than that of animals which sur vived the challenge (95.7 versus 223.6 mu g/ml, respectively). The IgG was further evaluated in mice challenged i.p. with a sublethal dose o f 5 x 10(4) CFU per mouse. Serial blood counts were performed on survi ving animals at 6, 12, 24, and 48 h. Surviving animals were sacrificed at 72 h, and bacterial counts were performed on their kidneys, livers , and peritoneal lavage fluids. Animals receiving I-IgG had lower bact erial counts in blood samples and lower bacterial densities in kidneys , livers, and peritoneal lavage samples than mice immunized with stand ard Ige (P < 0.05). These data suggest that S. aureus type 5 CP antibo dies induced by active immunization or administered by passive immuniz ation confer protection against S. aureus infections.