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.

Background: Prosthetic joint infection (PJI) is most commonly caused by skin-derived, biofilm-forming staphylococci, with Staphylococcus aureus being most virulent and MRSA becoming a substantial problem. Cephaloporins are almost universally used as prophylaxis against PJI, yet Methicillin - resistant S aureus (MRSA) is becoming increasingly common in hospitals, nursing homes and now in the community. Such strains are not susceptible to cephalorsporins or to a range of other antimicrobials. In view of this increasing antibiotic resistance, an alternative approach to preventing S. aureus PJI is needed, and we propose that vaccination is a promising approach. Having regard to the distinct pathogenesis of PJI, this must target key events in infection establishment, such as adhesion to the implant, via the plasma conditioning film, mediated by bacterial binding proteins. It must also have the potential to protect against all S. aureus regardless of antibiotic resistance profile. Fibronectin-binding protein-A (FnBP-A) is one example, but the potential of FnBP-A as a PJI vaccine candidate has not been thoroughly investigated and data in previous literature are contradictory.

Methods: Here, polyclonal rabbit antibody against recombinant(r) FnBP-A binding domain was produced and investigated for the first time for activity against S. aureus adhesion to rabbit plasma-conditioned steel coupons in-vitro.

Results: The adhesion of homologous S. aureus 8325-4 (fnbA+, fnbB+), and a heterologous MRSA arthroplasty isolate was significantly (p < 0.05) reduced when pre-exposed to anti-FnBP-A antiserum (un-purified and IgG-purified), compared to pre-exposure with pre-immune serum. This was not observed with mutant strain S. aureus DU5883 (fnbA?, fnbB?), indicating the involvement of FnBP-A – specific inhibitory antibody (IgG). Results clearly demonstrate the potential of rFnBP-A binding domain as a vaccine antigen for prevention of PJI and merit further investigation.

The implications of this are that vaccination using this peptide might be expected to protect patients about to undergo elective arthroplasty from infection with S aureus whatever its antibiotic susceptibility, so offering a realistic solution to the problem of increasing resistance.

Introduction: One of the most important mechanisms S. epidermidis uses to establish infection on biomaterials is biofilm formation, in which adhesion and the production of polysaccharide intercellular adhesin (PIA) are key factors. Non-steroidal anti-inflammatory drugs (NSAIDs) have been reported to inhibit S. epidermidis biofilm formation and may be useful in prevention or treatment of implant infections (1,2). The potential of these drugs was evaluated by determining the effects of the NSAIDs on bacterial growth, adhesion to bare and conditioned polymethyl-methacrylate (PMMA), on biofilm development, and on established biofilms.

Methods: A PIA-deficient mutant and wild type strain (gift of Prof. D. Mack, Hamburg) and 3 clinical isolates of S. epidermidis were used. The NSAIDs were salicylic acid, acetylsalicylic acid, ibuprofen and phenylbutazone. Their effects on bacterial growth rate and viability were assessed. For adhesion assay, bacteria were exposed to a 1mM concentration of each drug and allowed to adhere for 1h to bare or human plasma – conditioned PMMA before being sonicated and quantified by chemiluminescence and culture. For biofilm assays, bacteria were grown on silicone discs in the presence of various drug concentrations for 4 days before being sonicated and quantified as above. Mature (4 day) biofilms were also exposed to the drugs for a further 4 days and quantified similarly, to assess the effect on established biofilms.

Results: All NSAIDs tested significantly (P< 0.05) reduced the growth rate and viability of each strain, in a concentration – dependent manner. Reduction of adhesion was observed on bare PMMA suggesting interference with either vitronectin – binding protein or charge / hydrophobic interactions. This was independent of the effect on growth. However, adhesion to plasma – conditioned PMMA, presumably mediated by MSCRAMMs, was not significantly affected. Reduction of biofilm formation was observed for all strains and was concentration – dependent, suggesting that inhibition of PIA synthesis was not responsible. There was a significant effect on established biofilms, this was also concentration dependent.

Conclusions:

All four NSAIDs reduced S. epidermidis growth rate and viability, but at concentrations above those achievable therapeutically.