Abstract
Prosthetic joint infection (PJI) is an increasing problem and management commonly involves prosthesis removal with serious consequences. Biofilm-forming staphylococci are the most common causative organisms with Staphylococcus aureus being most virulent and methicillin-resistant Staphylococcus aureus (MRSA) more than doubling the infection mortality rate. Bacterial adhesion is an essential primary event in biofilm formation and infection establishment. The development of a novel combination vaccine programme to prevent staphylococcal PJI by directing antibody against factors involved in adhesion and biofilm formation, and investigation of S. aureus binding-domains as potential vaccine components for adhesion inhibition is described.
Selected target antigens included the S. aureus fibronectin-binding protein (FnBP) and iron-regulated surface determinant (IsdA), which have been shown to be important for infection establishment and predominantly bind to host fibronectin and fibrinogen respectively. Escherichia coli clones harbouring recombinant S. aureus binding-domain DNA sequences were used for expression and purification of antigen domains. In vitro antibody evaluation determined whether immune inhibition of bacteria - ligand binding can significantly impact on attachment to plasma-conditioned biomaterial (in presence of other bacterial ligands).
Adhesion of homologous and heterologous (MRSA PJI isolate) S. aureus to plasma-conditioned steel was significantly reduced (approximately 50 percent average reduction, p < 0.0001) when pre-exposed to anti-rFnBP-A antiserum (with pre-immune serum control) that was 50-fold more dilute than the actual titre from immunisation. Inhibition was related to ligand presence but not staphylococcal Protein A, and reduced adhesion was not observed with the mutant strain, indicating specific inhibitory antibody involvement, and demonstrating for the first time the potential of rFnBP-A for prevention of S. aureus PJI. Adhesion-inhibitory activity was also observed with a purified IgG-fraction of rIsdA antiserum but this activity appeared to be masked by non-IsdA - related interactions when non-IgG - purified antiserum was assessed.
Correspondence should be addressed to Dr Roger Bayston, Division of Orthopaedic and Accident Surgery, Queen’s Medical Centre, Nottingham, NG7 2UH, England.
