• Staphylococcus aureus evades the extracellular antimicrobial activity of mast cells by promoting its own uptake.

      Abel, Jens; Goldmann, Oliver; Ziegler, Christina; Höltje, Claudia; Smeltzer, Mark S; Cheung, Ambrose L; Bruhn, Daniela; Rohde, Manfred; Medina, Eva; Infection Immunology Research Group, Helmholtz Centre for Infection Research, Braunschweig, Germany. (2011)
      In this study, we investigated the interactions of Staphylococcus aureus with mast cells, which are multifunctional sentinels lining the surfaces of the body. We found that bone marrow-derived murine mast cells (BMMC) exerted a powerful phagocytosis-independent antimicrobial activity against S. aureus. Both the release of extracellular traps as well as discharge of antimicrobial compounds were the mechanisms used by the BMMC to kill extracellular S. aureus. This was accompanied by the secretion of mediators such as TNF-α involved in the recruitment of effector cells. Interestingly, S. aureus subverted the extracellular antimicrobial activity of the BMMC by internalizing within these cells. S. aureus was also capable to internalize within human mast cells (HMC-1) and within murine skin mast cells during in vivo infection. Bacteria internalization was, at least in part, mediated by the α5β1 integrins expressed on the surface of the mast cell. In the intracellular milieu, the bacterium survived and persisted by increasing the cell wall thickness and by gaining access into the mast cell cytosol. The expression of α-hemolysin was essential for staphylococci intracellular persistence. By hiding within the long-life mast cells, staphylococci not only avoid clearance but also establish an infection reservoir that could contribute to chronic carriage.
    • Staphylococcus aureus phenotype switching: an effective bacterial strategy to escape host immune response and establish a chronic infection.

      Tuchscherr, Lorena; Medina, Eva; Hussain, Muzaffar; Völker, Wolfgang; Heitmann, Vanessa; Niemann, Silke; Holzinger, Dirk; Roth, Johannes; Proctor, Richard A; Becker, Karsten; et al. (2011-03)
      Staphylococcus aureus is a frequent cause for serious, chronic and therapy-refractive infections in spite of susceptibility to antibiotics in vitro. In chronic infections, altered bacterial phenotypes, such as small colony variants (SCVs), have been found. Yet, it is largely unclear whether the ability to interconvert from the wild-type to the SCV phenotype is only a rare clinical and/or just laboratory phenomenon or is essential to sustain an infection. Here, we performed different long-term in vitro and in vivo infection models with S. aureus and we show that viable bacteria can persist within host cells and/or tissues for several weeks. Persistence induced bacterial phenotypic diversity, including SCV phenotypes, accompanied by changes in virulence factor expression and auxotrophism. However, the recovered SCV phenotypes were highly dynamic and rapidly reverted to the fully virulent wild-type form when leaving the intracellular location and infecting new cells. Our findings demonstrate that bacterial phenotype switching is an integral part of the infection process that enables the bacteria to hide inside host cells, which can be a reservoir for chronic and therapy-refractive infections.