Antibody response to Staphylococcus aureus surface proteins in rabbits with persistent osteomyelitis after treatment with demineralized bone implants

Abstract

A rabbit model was used to study the effect of allogeneic demineralized bone powder (DBP) implants on the persistence of Staphylococcus aureus osteomyelitis. Thirty-one rabbits with chronic osteomyelitis of the tibia established by day 21, were started on systemic antibiotics followed by either no additional treatment or debridement plus either DBP (with or without supplemental antibiotics) or supplemental antibiotics only. On day 21, cultures showed a mean of 2 x 10(4) CFU/mg of debrided osseous material. By day 70, the treatment most effective in clearing infection was found in animals treated with supplemental antibiotics only (mean of 142 +/- 116 CFU/mg). In contrast, infection persisted at a 7- to 10-fold-higher level in animals receiving DBP with and without supplemental antibiotics; these results suggest that DBP contributed to persistence of infection. Longitudinal sera were tested again staphylococcal sonic extracts by immunoblot. Detection of numerous probe-positive bands indicated complex but remarkably similar antibody responses among infected animals. Antibodies attached directly to the cell surfaces of staphylococci as shown by immunogold and blocked the binding of organisms to HEp-2 and human fetal lung cells in a radioadherence assay. Antibodies could be absorbed out by intact organisms and were unreactive by immunoblot against antigens derived from cells pretreated with pronase, proteinase K, or lysostaphin. These results indicate that the major response was directed against staphylococcal cell surface proteins. Surprisingly, only one major band (molecular weight, approximately 12,000) was detected when a homologous in vivo antigen preparation was studied by immunoblot. Antibody reactive against this peptide did not appear to react with staphylococci grown in vitro.