Staphylococcal aureus (S. aureus), a Gram-positive bacteria, is known to cause various infections. Extracellular vesicles (EVs) are a heterogeneous array of membranous structures secreted by cells from all three domains of life, i.e., eukaryotes, bacteria, and archaea. Bacterial EVs are implied to be involved in both bacteria–bacteria and bacteria–host interactions during infections. It is still unclear how S. aureus EVs interact with host cells and induce inflammatory responses. In this study, EVs were isolated from S. aureus and mutant strains deficient in either prelipoprotein lipidation (Δlgt) or major surface proteins (ΔsrtAB). Their immunostimulatory capacities were assessed both in vitro and in vivo. We found that S. aureus EVs induced pro-inflammatory responses both in vitro and in vivo. However, this activity was dependent on lipidated lipoproteins (Lpp), since EVs isolated from the Δlgt showed no stimulation. On the other hand, EVs isolated from the ΔsrtAB mutant showed full immune stimulation, indicating the cell wall anchoring of surface proteins did not play a role in immune stimulation. The immune stimulation of S. aureus EVs was mediated mainly by monocytes/macrophages and was TLR2 dependent. In this study, we demonstrated that not only free Lpp but also EV-imbedded Lpp had high pro-inflammatory activity.

Staphylococcus aureus (S. aureus) causes a broad range of infections. Toll-like receptor (TLR) 2 senses the S. aureus lipoproteins in S. aureus infections. Aging raises the risk of infection. Our aim was to understand how aging and TLR2 affect the clinical outcomes of S. aureus bacteremia. Four groups of mice (wild type/young, wild type/old, TLR2^−/−/young, and TLR2^−/−/old) were intravenously infected with S. aureus, and the infection course was followed. Both TLR2 deficiency and aging enhanced the susceptibility to disease. Increased age was the main contributing factor for increased mortality rates and changes in spleen weight, whereas other clinical parameters, such as weight loss and kidney abscess formation, were more TLR2 dependent. Importantly, aging increased mortality rates without relying on TLR2. In vitro, both aging and TLR2 deficiency down-regulated cytokine/chemokine production of immune cells with distinct patterns. In summary, we demonstrate that aging and TLR2 deficiency impair the immune response to S. aureus bacteremia in distinct ways.

Introduction: Septic arthritis, primarily caused by Staphylococcus aureus (S. aureus), is a severe joint infection that leads to joint and bone damage. S. aureus lipoproteins (LPPs) bind to Toll-like Receptor 2 (TLR2), inducing arthritis and localized bone loss. Aging affects TLR2 immune response to pathogens. While intra-articular injections of S. aureus LPPs induces local bone resorption in mice, the influence of aging and TLR2 expression on bone mineral density (BMD) after S. aureus bacteremia remains unclear. Methods: We analyzed distal femoral BMD in young and old TLR2 knock-out and wild-type mice following intravenous S. aureus infection. BMD was measured in both total and trabecular bone in old and young mice to determine age and TLR2-dependent responses to infection. Results: In non-infected mice, BMD in both total and trabecular bone was mainly age-related and TLR2-independent. Following S. aureus bacteremia, young wild-type mice with TLR2 expression showed decreased combined cortical and trabecular BMD. This effect was absent in aged mice or TLR2 deficient mice. Focal septic arthritis, induced by S. aureus bacteremia, emerged as the primary cause to bone loss in the femur metaphysis. TLR2 appears to play a crucial role in focal septic arthritis-induced bone loss, as evidenced by in vitro findings demonstrating that staphylococcal LPPs, known TLR2 agonists, increase the Tnfsf11/Tnfrsf11b ratio in mouse pariosteal osteoblasts. Conclusion: S. aureus bacteremia triggers local bone loss in murine arthritis, depending on both age and TLR2 expression.

Septic arthritis, the most severe joint disease, is frequently caused by Staphylococcus aureus ( S . aureus ). A substantial proportion of patients with septic arthritis experience poor joint outcomes, often necessitating joint replacement surgery. Here, we show that monocyte depletion confers full protection against bone erosion in a septic arthritis mouse model. In the infected synovium, Ly6C ^hi monocytes exhibited increased expression of osteoclastogenesis-related molecules, including CCR2, c-Fms, and RANK. S . aureus lipoproteins induced elevated levels of RANKL, MCSF, and CCL2 in joints, with synovial fibroblasts identified as the major RANKL producer. Anti-RANKL treatment prevented bone destruction in both local and hematogenous septic arthritis murine models. Importantly, combining anti-RANKL treatment with antibiotics provided robust protection against joint damage. Our results indicate that the infiltration and transformation of monocytes into bone-destructive, osteoclast-like cells are key mechanisms in septic arthritis. Combining anti-RANKL and antibiotic therapy represents a promising therapy against this devastating disease.

Staphylococcal toxic shock syndrome (STSS) is a rare, yet potentially fatal disease caused by Staphylococcus aureus (S. aureus) enterotoxins, known as superantigens, which trigger an intense immune response. Our previous study demonstrated the protective effect of tofacitinib against murine toxin-induced shock and a beneficial effect against S. aureus sepsis. In the current study, we examined the effects of tofacitinib on T-cell response in peripheral blood using a mouse model of enterotoxin-induced shock. Our data revealed that tofacitinib suppresses the activation of both CD4+ and CD8+ T cells in peripheral blood. Furthermore, both gene and protein levels of Th1 cytokines were downregulated by tofacitinib treatment in mice with enterotoxin-induced shock. Importantly, we demonstrated that CD4+ cells, but not CD8+ cells, are pathogenic in mice with enterotoxin-induced shock. In conclusion, our findings suggest that tofacitinib treatment suppresses CD4+ T-cell activation and Th1 response, thereby aiding in protection against staphylococcal toxic shock in mice. This insight may guide the future development of novel therapies for STSS.

Polycyclic polyprenylated acylphloroglucinols (PPAPs) comprise a large group of compounds of mostly plant origin. The best-known compound is hyperforin from St. John’s wort with its antidepressant, antitumor and antimicrobial properties. The chemical synthesis of PPAP variants allows the generation of compounds with improved activity and compatibility. Here, we studied the antimicrobial activity of two synthetic PPAP-derivatives, the water-insoluble PPAP23 and the water-soluble sodium salt PPAP53. In vitro, both compounds exhibited good activity against methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus faecium. Both compounds had no adverse effects on Galleria mellonella wax moth larvae. However, they were unable to protect the larvae from infection with S. aureus because components of the larval coelom neutralized the antimicrobial activity; a similar effect was also seen with serum albumin. In silico docking studies with PPAP53 revealed that it binds to the F1 pocket of human serum albumin with a binding energy of −7.5 kcal/mol. In an infection model of septic arthritis, PPAP23 decreased the formation of abscesses and S. aureus load in kidneys; in a mouse skin abscess model, topical treatment with PPAP53 reduced S. aureus counts. Both PPAPs were active against anaerobic Gram-positive gut bacteria such as neurotransmitter-producing Clostridium, Enterococcus or Ruminococcus species. Based on these results, we foresee possible applications in the decolonization of pathogens.