'Guilty by association' - Protein-protein interactions (PPIs) in bacterial pathogens

Protein-protein interaction (PPI) studies are frequently used as a starting point for the functional annotations of unknown proteins according to the principle of 'guilty by association'. Moreover, they deliver information for the understanding of specific virulence mechanisms. We provide an overview about the approaches used for the identification of PPIs in human bacterial pathogens, commenting on advantages and pitfalls of the methods. Furthermore, this review intends to show the impact of PPI studies on future research, taking Helicobacterpylori, one of the first sequenced human pathogens, as model organism.