Mechanisms of protective immunity to Staphylococcus aureus infection in humans remain elusive. While the importance of cellular immunity has been shown in mice, T cell responses in humans have not been characterised. Using a murine model of recurrent S. aureus peritonitis, we demonstrated that prior exposure to S. aureus enhanced IFNγ responses upon subsequent infection, while adoptive transfer of S. aureus antigen-specific Th1 cells was protective in naïve mice. Translating these findings, we found that S. aureus antigen-specific Th1 cells were also significantly expanded during human S. aureus bloodstream infection (BSI). These Th1 cells were CD45RO+, indicative of a memory phenotype. Thus, exposure to S. aureus induces memory Th1 cells in mice and humans, identifying Th1 cells as potential S. aureus vaccine targets. Consequently, we developed a model vaccine comprising staphylococcal clumping factor A, which we demonstrate to be an effective human T cell antigen, combined with the Th1-driving adjuvant CpG. This novel Th1-inducing vaccine conferred significant protection during S. aureus infection in mice. This study notably advances our understanding of S. aureus cellular immunity, and demonstrates for the first time that a correlate of S. aureus protective immunity identified in mice may be relevant in humans.

dPrevious research on Staphylococcus aureus in pigs focused on livestock-associated methicillin-resistant S. aureus (MRSA) and had a qualitative cross-sectional design. This study aimed to elucidate the frequency, load, and stability of S. aureus nasal carriage in pigs over time and investigated possible associations between carriage and immune response. Nasal swabs were collected three times weekly from 480 tagged adult pigs in 20 Danish production farms. S. aureus and MRSA were quantified on selective media by the most-probable-number method. The levels of IgG against 10 S. aureus antigens in serum were quantified in selected pigs by a Luminex assay. All the farms were positive for S. aureus and 15 for MRSA, leading to overall prevalences of persistent and intermittent carriers and noncarriers of 24, 52, and 23%, respectively. Carriage frequency and nasal loads were significantly higher on MRSA-positive farms. Logistic-regression modeling revealed the presence of individual pigs characterized by high nasal loads (>10,000 CFU per swab) and stable carriage regardless of farm-and pen-associated factors. On the other hand, the humoral response was strongly influenced by these environmental factors. The existence of a minority of shedders contributing to maintenance of S. aureus within farms opens up new perspectives on the control of MRSA in pig farming.

Determinants of bacterial colonization in children have been described. In the Generation R Study, a population-based cohort study, we determined whether the colonization statuses of mothers and children are correlated. Such a correlation was observed for Staphylococcus aureus and Haemophilus influenzae. Direct transmission, genetic susceptibility and/or unidentified environmental factors may play a role here.

Staphylococcus aureus causes a variety of infections. Knowledge about the physiological role of most S. aureus antigens in colonization and infection is only limited. This can be studied by measuring antigen-specific antibody responses. In this study, we optimized the multiplex microsphere bead-based flow cytometry technique for mouse serum samples. We analysed immunoglobulin G (IgG) levels directed against 26 S. aureus proteins in a single small-volume mouse serum sample. We assessed possible cross reactivity. Furthermore, we analysed serum samples from mice with different types of S. aureus infections caused by different S. aureus strains. The results show that cross reactivity between proteins on microspheres and serum antibodies towards other proteins was limited. We found that lung-infected mice had a higher and broader IgG response than skin-infected mice. Clearly, the site of infection influences the IgG profile. Next, we compared sera from mice with intravenously-induced bacteraemia caused by different S. aureus strains. We showed different IgG responses depending on the causing S. aureus strain. It is concluded that the bead-based multiplex S. aureus antibody assay can be successfully applied to determine the immunogenicity of different S. aureus proteins in relation to the site of infection and the S. aureus strain causing the infection.