The Clp system and, in particular, the subunit ClpX are implicated in infection-related aspects of S. aureus physiology and thus the Clp components are involved in infection-relevant stress responses as those mounted upon oxidative stress (19, –, 21), oxygen limitation (20, 22, 23), heat or cold shock (19, 24), and iron limitation (25, 26). Here, CLPX is linked to infection.