Staphylococci express a 42 kDa cell-wall-associated
protein which functions as a receptor for the mammalian
iron-binding
glycoprotein transferrin. To determine whether this
transferrin-
binding protein (
TBP) is expressed during
infection, Staphylococcus aureus and Staphylococcus epidermidis were grown in vivo in chambers implanted intraperitoneally in rats. SDS-PAGE and Western blotting of cell wall
proteins prepared from staphylococci recovered directly from the chambers revealed the presence of both the
TBP and bacterial-surface-associated rat
transferrin. To obtain evidence for the in vivo expression of the staphylococcal
TBPs in humans, sera and human peritoneal
dialysate (HPD) from non-infected patients undergoing
continuous ambulatory peritoneal dialysis (
CAPD) and sera from healthy human volunteers were screened for anti-
TBP antibodies. Western immunoblots revealed that three out of ten samples from the latter group, seven out of ten HPD samples and ten of ten
CAPD patient serum samples contained
antibodies to the
TBP of both S. aureus and S. epidermidis. To gain further insights into the appearance of
TBP antibodies, HPD samples were collected over time from
CAPD patients whose HPD samples taken immediately after
catheter insertion lacked anti-
TBP antibodies. In two of these patients, each of whom experienced an episode of
peritonitis due to S. epidermidis or Staphylococcus hominis,
antibodies to the
TBP appeared in the HPD collected immediately post-
infection. To determine whether such
TBP antibodies were capable of blocking interactions between
transferrin and its staphylococcal receptor, HPD
immunoglobulin fractions were purified using
protein A-Sepharose beads. In competition assays, these
immunoglobulins blocked the binding of 125I-labelled
transferrin both to whole bacteria and to the isolated 42 kDa
TBPs of S. aureus and S. epidermidis. These provide evidence to show that staphylococcal
TBPs are expressed in vivo during
infection.