Staphylococcus aureus phenotype switching: an effective bacterial strategy to escape host immune response and establish a chronic infection

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.