Molecular mechanisms of Staphylococcus aureus nasopharyngeal colonization

Staphylococcus aureus is responsible for a wide range of different infections ranging in severity from mild to fatal. However, it primarily exists as a commensal organism in a number of different anatomical sites including the nasopharynx. Although colonization itself is a harmless state, colonized individuals are at risk of endogenous infection when S. aureus enters otherwise sterile sites via wounds or indwelling medical devices. As such, studies of colonization may identify important targets for vaccines or other prophylactic approaches. Colonization is a dynamic process; S. aureus must attach to host surfaces, overcome immune components and compete with other commensal microbes. This occurs via a number of surface-attached and secreted proteins and other factors such as wall teichoic acid. In addition, colonizing S. aureus must constantly replicate to maintain its niche and exclude other strains. These myriad interactions provide a strong selective pressure for the maintenance or enhancement of mechanisms of adhesion, invasion and immune evasion. The evolutionary implications of this may explain why S. aureus is such a capable pathogen because many of the proteins involved in colonization have also been identified as virulence factors. This review describes the diverse molecular mechanisms used by S. aureus to colonize the host and discusses how the pressures that have selected for these may have led to its virulence.