The importance of a collagen-binding adhesin in the pathogenesis of septic arthritis has been examined by comparing the virulence of two sets of Staphylococcus aureus mutants in an animal model. Collagen adhesin-negative mutant PH100 was constructed by replacing the chromosomal collagen adhesin gene (cna) in a clinical strain, Phillips, with an inactivated copy of the gene. Collagen adhesin-positive mutant S. aureus CYL574 was generated by introducing the cna gene into CYL316, a strain that normally lacks the cna gene. Biochemical, immunological, and functional analyses of the generated mutants and their respective parent strains showed that binding of 1251-labeled collagen, expression of an immunoreactive collagen adhesin, and bacterial adherence to cartilage were directly correlated with the presence of a functional cna gene. Greater than 70% of the mice injected with the Cna+ strains developed clinical signs of arthritis, whereas less than 27% of the animals injected with Cna-strains showed symptoms of disease. Furthermore, mice injected with the Cna+ strain Phillips had remarkably elevated levels of immunoglobulin Gl and interleukin-6 compared with mice injected with the Cnamutant PH100. Taken together, these results demonstrate that collagen adhesin plays an important role in the pathogenesis of septic arthritis induced by S. aureus.

We have studied the role of the accessory gene regulator (agr) of Staphylococcus aureus as a virulence determinant in the pathogenesis of septic arthritis. At least 15 genes coding for potential virulence factors in Staphylococcus aureus are regulated by a putative multicomponent signal transduction system encoded by the agr/hld locus. agr and hid mutants show a decreased synthesis of extracellular toxins and enzymes, such as alpha-, beta-, and delta-hemolysin, leucocidin, lipase, hyaluronate lyase, and proteases, and at the same time an increased synthesis of coagulase and protein A as compared with the wild-type counterpart. We have used a recently described murine model of S. aureus-induced arthritis to study the virulence of S. aureus 8325-4 and two agrihld mutants derived from it. Sixty percent of the mice in,jected with the wild-type strain developed arthritis, whereas agrA and hid mutants displayed joint involvement in only 10 and 30%o, respectively. In addition, 40% of the mice inoculated with the wild-type strain displayed an erosive arthropathy; such changes were not detectable at all in mice inoculated with the agrA mutant. Serum levels of interleukin-6, a potent B-cell differentiation factor, were significantly higher (P < 0.001) in the mice inoculated with the wild-type strain than in those inoculated with the agrA mutant counterpart. Overall, our results suggest that the agr system of S. aureus is an important virulence determinant in the induction and progression of septic arthritis in mice.

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In a newly developed mouse model of Staphylococcus aureus arthritis the kinetics of joint destruction and serological manifestations as well as the clinical course of arthritis and osteitis were studied. Almost all mice developed histopathological signs of arthritis upon a single intravenous injection of 107 S. aureus LS-1 cells. There was rapid joint destruction, with synovial hypertrophy already visible, within 24 h after injection of the bacteria. Cartilage and/or bone erosions were seen in a majority of the mice within 72 h. Extra-articular manifestations, especially signs of bone infection, were also found soon after inoculation of the bacteria. Tail osteitis was frequent (50% of the mice) but appeared later than arthritis. Polymorphonuclear cells prevailed in the early joint lesions and were also common in the extra-articular manifestations. Within 3 days, mononuclear cells were also seen in the inflamed synovium, gaining a dominant position 3 weeks after the start of the disease. Serum interleukin-6 levels were already increased within 6 h after bacterial injection and remained elevated throughout the course of arthritis. Serum tumor necrosis factor levels were increased within 24 h. There was a tremendous induction of immunoglobulin production, especially of the immunoglobulin Gl isotype. This was paralleled by the production of specific antibodies to S. aureus (cell walls and toxin), as well as autoantibodies (rheumatoid factors and anti-single-stranded DNA antibodies), all predominantly of the immunoglobulin G isotype. The type and magnitude of the immunoglobulin G response together with the elevated interleukin-6 levels speak in favor of both antigen-specific and polyclonal B-cell activation during S. aureus arthritis. This study points out important similarities between our new model of S. aureus arthritis and human S. aureus arthritis. This resemblance will enable controlled studies of pathogenetic mechanisms of septic arthritis as well as therapeutic and prophylactic approaches. Bacterial arthritis is a rapidly progressive and highly destructive joint disease in humans. Other destructive joint diseases, including inflammatory disorders, such as rheumnatoid arthritis, are connected to an increased incidence of bacterial arthritis (14). Also, certain forms of surgical and medical therapy such as joint implants and immunosuppressive treatment, are connected to an increased frequency of bacterial arthritis (14). Staphylococcus aureus is the causative agent in about 60% of cases of nongonococcal bacterial arthritis (10). In patients with rheumatic diseases, this figure is even higher, approaching 75% (11). Laboratory models of bacterial arthritis have been used previously (12, 17, 21, 24, 25, 28, 30, 31, 33-35). In most instances, bacteria have been injected intra-articularly, usually with rabbits as experimental animals. In contrast, human bacterial arthritis usually spreads in a hematogenous manner (14). We recently reported a spontaneous outbreak of S. aureus arthritis in our mouse colony (3) and desc...

Staphylococcus aureus is a major cause of nosocomial and community-acquired infections. Morbidity and mortality due to infections such as sepsis, osteomyelitis, septic arthritis, and invasive endocarditis remain high despite the use of antibiotics. The emergence of antibiotic resistant super bugs mandates that alternative strategies for the prevention and treatment of S. aureus infections are developed. We investigated the ability of vaccination with a recombinant fragment of the S. aureus collagen adhesin to protect mice against sepsis-induced death. Actively immunized NMRI mice were intravenously inoculated with the S. aureus clinical isolate strain Phillips. 14 d after inoculation, mortality in the collagen adhesin-vaccinated group was only 13%, compared with 87% in the control antigen immunized group (P < 0.001). To determine if the protective effect was antibody mediated, we passively immunized naive mice with collagen adhesin-specific antibodies. Similar to the active immunization strategy, passive transfer of collagen adhesin-specific antibodies protected mice against sepsis-induced death. In vitro experiments indicated that S. aureus opsonized with sera from collagen adhesin immunized mice promoted phagocytic uptake and enhanced intracellular killing compared with bacteria opsonized with sera from control animals. These results indicate that the collagen adhesin is a viable target in the development of immunotherapeutics against S. aureus.