The role of zinc in the interplay between pathogenic streptococci and their hosts

Recent studies on pathogenic streptococci have revealed that zinc is a pivotal metal ion in their interaction with the host. In these streptococci, systems exist that ensure optimal use of zinc from the surrounding milieu, as well as export of zinc when concentrations exceed tolerance levels. Zinc uptake is of crucial importance for the virulence of streptococci, whereas elevated zinc levels induced in the host during infection are detrimental for these pathogens. The expression or activity of a number of putative surface proteins and virulence factors depends on zinc. Moreover, several metal sensor proteins that mediate the transcriptional response to zinc in streptococci have recently been characterized. A number of components of zinc- and other metal ion-acquisition systems are suitable as protective antigens and may be future targets for the development of new vaccines, thus providing opportunities for the development of novel therapies. This review will discuss the recent advancements in the important field of metal ion biology in relation to the virulence of pathogenic streptococci, with a central focus on zinc homeostasis in Streptococcus pneumoniae.