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Staphylococcus aureus but not Staphylococcus epidermidis can acquire iron from transferrin.

Staphylococci grow and cause infection under the iron-restricted conditions found in vivo. They therefore must possess mechanisms to obtain iron for metabolism from this environment. To determine if staphylococci can extract iron bound to human transferrin, we labelled transferrin with 55Fe and performed uptake assays on cells grown in iron-restricted and iron-plentiful conditions. Growing cultures of Staphylococcus aureus NCTC 8532 could take up radioactive iron during mid- to late-exponential phase of growth. This process was iron-regulated and did not require direct contact between the cell and the labelled transferrin. Siderophore production was detected during this phase, but reductase or protease activity was not. S. epidermidis ATCC 14990 could not access 55Fe bound to transferrin, nor did this isolate produce siderophore, reductase or protease. This difference in the ability to acquire iron bound to transferrin may contribute to the increased virulence of S. aureus when compared to S. epidermidis.