A small membrane protein critical to both the offensive and defensive capabilities of Staphylococcus aureus.

Staphylococcus aureus is a major human pathogen, where the widespread emergence of antibiotic resistance is making infections more challenging to treat. Toxin induced tissue damage and resistance to the hosts immune system are well established as critical to its ability to cause disease. However, recent attempts to study S. aureus pathogenicity at a population level have revealed significant complexity and hierarchical levels of regulation. In an effort to better understand this we have identified and characterized a principle effector protein, MasA. The inactivation of this small highly-conserved membrane protein simultaneously disrupts toxin production and impairs S. aureus ability to resist several aspects of the innate immune system. These pleiotropic effects are mediated by both a change in the stability of the bacterial membrane and the dysregulation of iron homeostasis, which results in a significant impairment in the ability of S. aureus to cause infection in both a subcutaneous and a sepsis model of infection. That proteins with such major effects on pathogenicity remain unidentified in a bacterium as well studied as S. aureus demonstrates how incomplete our understanding of their ability to cause disease is, an issue that needs to be addressed if effective control and treatment strategies are to be developed.