Tomas Bremell

Vaccination with a recombinant fragment of collagen adhesin provides protection against Staphylococcus aureus-mediated septic death.

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.

The role of Staphylococcus aureus sortase A and sortase B in murine arthritis

Gram-positive pathogenic bacteria display proteins on their surface that play important roles during infection. In Staphylococcus aureus, these surface proteins are anchored to the cell wall by two sortase enzymes, SrtA and SrtB, that recognize specific surface protein sorting signals. The role of sortase enzymes in bacterial virulence was examined using a murine septic arthritis model. Intravenous inoculation with any of the Delta(srtA), Delta(srtB) or Delta(srtAB) mutants resulted in significantly increased survival and significantly lower weight loss compared with the parental strain. Mice inoculated with the Delta(srtA) mutant did not express severe arthritis, while arthritis in mice inoculated with the Delta(srtB) mutant was not different from that seen in mice that were infected with the wild-type parent strain. Furthermore, persistence of staphylococci in kidneys and joints following intravenous inoculation of mice was more pronounced for wild-type and Delta(srtB) mutant strains than for Delta(srtA) or Delta(srtAB) variants. Together these results indicate that sortase B (srtB) plays a contributing role during the pathogenesis of staphylococcal infections, whereas sortase A (srtA) is an essential virulence factor for the establishment of septic arthritis.

On the Role of Staphylococcus aureus Sortase and Sortase-Catalyzed Surface Protein Anchoring in Murine Septic Arthritis

Anchoring of Staphylococcus aureus surface protein to the cell wall is catalyzed by sortase, a transpeptidase. The contribution of staphylococcal surface proteins to establishment of infection was examined using a murine septic arthritis model. Intravenous inoculation of mice with the sortase-deficient mutant S. aureus strain SMK3 did not result in weight loss or severe septic arthritis, in contrast to the parent strain, S. aureus Newman. Direct inoculation of the sortase mutant into joint cavities also failed to cause severe synovitis or erosive arthritis. Furthermore, intravenous inoculation with staphylococci resulted in the rapid clearing of the sortase mutant from the bloodstream. This phenomenon demonstrates the involvement of host neutrophils; when these cells were depleted, sortase mutant staphylococci caused severe systemic infection, although not septic arthritis. These results suggest that sortase mutant staphylococci are significantly less virulent than the parent strain, Newman: the sortase mutant has decreased ability to reach target organs and, once there, to induce an inflammatory response.

Role of T Lymphocytes in Experimental Staphylococcus aureus Arthritis

Using a recently developed murine model of haematogenously induced Staphylococcus aureus, the authors have characterized the phenotypes and functional properties of inflammatory cells present in the synovium of arthritic mice. The results show that large numbers of granulocytes and macrophages were observed in the inflamed synovia within 24 h of inoculation of S. aureus strain LS‐1. Many of the synovial macrophage‐like cells stained for cytoplasmic IL‐1α and TN F‐α. Subsequently (< 48 h later), a prominent infiltration of T lymphocytes, predominantly of CD4+ phenotype, was observed. Some of the T lymphocytes stained for IL‐2 receptor and intracytoplasmicinterferon‐γ (IFN‐γ). Surprisingly, in spite of the severe inflammatory process, very few cells expressed MHC class‐II molecules in the arthritic synovia. In addition, in vivo depletion of CD4 + T‐cells resulted in a considerably milder course of staphylococcal arthritis. The similarities in the phenotype expression of synovial cells and central role of T‐cells in S. aureus arthritis as well as in non‐infectious models of arthritis, indicate that the process governing joint destruction is likely to be the same, irrespective of the initial stimulus.

Inhibition of nitric oxide synthase (NOS) aggravates Staphylococcus aureus septicaemia and septic arthritis

The aim of this study was to assess the role of NO and its metabolites in bacterial arthritis. The murine model of haematogenously acquired septic arthritis was used. Swiss mice treated with NOS inhibitors (NG‐monomethyl‐L‐arginine or Nω‐nitro‐L‐arginine methyl ester) were injected intravenously with toxic shock syndrome toxin‐1 (TSST‐1) producing Staphylococcus aureus LS‐1. Arthritis was evaluated clinically and histopathologically. Serum cytokine levels, bacterial isolates and intracellular capacity of macrophages to kill bacteria were also analysed. The frequency of arthritis in mice treated with NOS inhibitors was three to four‐fold higher than that in non‐treated controls (75% versus 20%). The severity of arthritis, expressed as mean arthritic index, was 1.4 and 0.4, respectively. Cartilage and/or bone destruction occurred in 63% of NOS inhibitor‐treated mice, but only in 10% of controls. Also, the cumulative septicaemia‐induced mortality was clearly higher in mice treated with NOS inhibitors compared with non‐treated controls. Intracellular killing capacity of the peritoneal macrophages, treated in vitro with NOS inhibitors, was decreased. Thus, 24 h after bacterial inoculation peritoneal macrophages pretreated with NOS inhibitors killed more than 10 times less bacteria than the control ones (P < 0.01). We conclude that NOS inhibitors aggravate S. aureus arthritis, possibly by inducing impairment of the intracellular killing capacity of macrophages.

Protective role of NK1.1+ cells in experimental Staphylococcus aureus arthritis

In a model of Staphylococcus aureus‐induced septic arthritis in C57Bl/6 mice we investigated the role of natural killer (NK) cells in the development of disease. Depletion of NK1.1+ cells was achieved by repeated injections of the PK136 antibody, whereas control mice received an irrelevant monoclonal antibody, O1C5.B2. Both groups of mice then received injections intravenously with 2 × 107 live S. aureus LS‐1 secreting toxic shock syndrome toxin‐1 (TSST‐1). The mice were evaluated for 16 days with regard to weight, mortality and arthritis. Nine days after bacterial injection, 9/19 mice depleted of NK cells had developed arthritis compared with 1/17 in the control group (P = 0.01). The experiment was repeated twice with the same outcome. NK cell‐depleted and control mice displayed the same degree of histopathological signs of arthritis at day 16. Depletion of NK cells did not affect uptake of bacteria by phagocytic cells in vitro, or bacterial clearance in vivo. In NK cell‐depleted mice there was a tendency to increased levels of antibodies to TSST‐1, whereas total immunoglobulin levels were similar to those in controls. NK cell depletion of non‐infected mice did not affect the magnitude of inflammatory response during the T cell‐dependent cutaneous DTH reaction to oxazolone, or during granulocyte‐mediated inflammation. However, specific antibody responses to oxazolone were greatly increased in depleted animals. In conclusion, our study demonstrates that NK cells protect against arthritis during S. aureus infection. This outcome does not seem to be due to an influence on bacterial clearance, but could be due to an interaction with the host anti‐inflammatory mechanisms.

Complement depletion aggravates Staphylococcus aureus septicaemia and septic arthritis

The aim of the study was to assess the role of the complement system in Staphylococcus aureus arthritis and septicaemia. The murine model of haematogenously acquired septic arthritis was used, injecting intravenously toxic shock syndrome toxin‐1 (TSST‐1), producing S. aureus LS‐1. Complement was depleted using cobra venom factor (CVF). Evaluation of arthritis was performed clinically and histopathologically. In addition, the effect of complement depletion on the phagocytic activity of leucocytes was assessed in vivo and in vitro. Six days after inoculation of S. aureus the prevalence of arthritis in decomplemented mice was three‐fold higher than that in controls (91% versus 25%). The clinical severity of arthritis at the end of the experiment, expressed as arthritic index, was 7.3 and 1.9, respectively. These findings were confirmed by histological index of synovitis as well as of cartilage and/or bone destruction being significantly higher in decomplemented mice than in controls (9.8 ± 1.7 versus 4.9 ± 1.2, P < 0.05; and 7.9 ± 1.7 versus 3.0 ± 0.9, P < 0.05, respectively). Also, the septicaemia‐induced mortality was clearly higher in decomplemented mice compared with the controls. CVF treatment significantly reduced in vivo polymorphonuclear cell‐dependent inflammation induced by subcutaneous injection of olive oil and mirroring the capacity of polymorphonuclear cells (PMNC) to migrate and/or extravasate. Besides, the decomplementation procedure significantly impaired phagocytic activity of peripheral blood leucocytes in vitro, since the number of phagocytes being able to ingest bacteria decreased by 50% when the cells were maintained in decomplemented serum compared with those in intact serum. The conclusion is that complement depletion aggravates the clinical course of S. aureus arthritis and septicaemia, possibly by a combination of decreased migration/extravasation of PMNC and an impairment of phagocytosis.

Staphylokinase Promotes the Establishment of Staphylococcus aureus Skin Infections While Decreasing Disease Severity

Skin infections are frequently caused by Staphylococcus aureus and can lead to a fatal sepsis. The microbial mechanisms controlling the initiation and progression from mild skin infection to a severe disseminated infection remain poorly understood. Using a combination of clinical data and in vitro and ex vivo assays, we show that staphylokinase, secreted by S. aureus, promoted the establishment of skin infections in humans and increased bacterial penetration through skin barriers by activating plasminogen. However, when infection was established, the interaction between staphylokinase and plasminogen did not promote systemic dissemination but induced the opening and draining of abscesses and decreased disease severity in neutropenic mice. Also, increased staphylokinase production was associated with noninvasive S. aureus infections in patients. Our results point out the dual roles of staphylokinase in S. aureus skin infections as promoting the establishment of infections while decreasing disease severity.

DISAbILITy OF THe ARM, SHOULDeR AND HAND qUeSTIONNAIRe IN SweDISH pATIeNTS wITH RHeUMATOID ARTHRITIS: A vALIDITy STUDy

OBJECTIVE The aim of this study was to assess the reliability and validity of the Disability of the Arm, Shoulder and Hand (DASH) questionnaire in a Swedish rheumatoid arthritis population. METHODS To investigate the concurrent and convergent validity, 67 patients with rheumatoid arthritis completed the DASH, the Health Assessment Questionnaire Disability Index (HAQ) and activity-induced pain. Active shoulder-arm motion, handgrip force and disease activity (Disease Activity Score in 28 joints; DAS28) were assessed. The test-retest reliability was investigated in 26 patients. Face validity was also investigated. RESULTS Spearmans correlation coefficient revealed a significant association (p

Expression of the mucosal lymphocyte integrin aEß7 and its ligand E-cadherin in salivary glands of patients with Sjögren's syndrome

The expression of the mucosal lymphocyte integrin alphaEbeta7 and its ligand E-cadherin was analyzed in sialadenitic lesions of patients with Sjögrens syndrome in order to assess the potential interactions between the mucosal and the systemic immunological compartments. Immunohistochemical evaluation of the inflammatory infiltrates in the salivary gland tissues in Sjögrens syndrome patients revealed presence of alphaEbeta7-integrin-expressing lymphocytes, in 18 of 20 biopsies examined. The ligand for alphaEbeta7, E-cadherin was also found in 18 of 20 salivary gland biopsies analysed. These results suggest homing of lymphocytes derived from the gut epithelium through the blood stream to inflamed salivary gland tissue followed by in situ interaction with E-cadherin expressing cells, the ligand for alphaEbeta7 expressing T lymphocytes.