Transferrin and Lactoferrin - Human Iron Sources for Enterococci

To overcome limitations in iron acquisition, enterococci have evolved a number of mechanisms to scavenge iron from the host iron-binding proteins - transferrin (TR) and lactoferrin (LF). The aim of this study was to demonstrate the mechanisms by which enterococci utilize human TR and LF bound iron. The study included two strains of Enterococcus faecalis grown in iron-deficient and iron-excess media respectively. The binding activity of both proteins was monitored using proteins labelled with 125I. The uptake of iron by enterococci was determined using 59Fe labelled proteins. Reduction of iron bound to TR and LF was assayed with ferrozine. The proteolytic cleavage of TR and LF was visualized by SDS-polyacrylamide gel electrophoresis. The siderophore activity was measured with chrome azurol S. The study revealed that enterococci use several ways to acquire iron from TR and LF, such as iron chelating siderophores, iron reduction - facilitated iron release, protein degradation - promoted iron release, and receptor mediated capture of the iron-host protein complexes. The broad spectrum of iron acquisition mechanisms used by enterococci may play a significant role in the colonization of the human body and the resulting pathogenicity.