THE STAPHYLOCOCCUS-AUREUS AND STAPHYLOCOCCUS-EPIDERMIDIS TRANSFERRIN-BINDING PROTEINS ARE EXPRESSED IN-VIVO DURING INFECTION

Staphylococci express a 42 kDa cell-wall-associated protein which func tions as a receptor for the mammalian iron-binding glycoprotein transf errin. To determine whether this transferrin-binding protein (TBP) is expressed during infection, Staphylococcus aureus and Staphylococcus e pidermidis were grown in vivo in chambers implanted intraperitoneally in rats. SD5-PAGE and Western blotting of cell wall proteins prepared from staphylococci recovered directly from the chambers revealed the p resence of both the TBP and bacterial-surface-associated rat transferr in. To obtain evidence for the in vivo expression of the staphylococca l TBPs in humans, sera and human peritoneal dialysate (HPD) from non-i nfected patients undergoing continuous ambulatory peritoneal dialysis (CAPD) and sera from healthy human volunteers were screened for anti-T BP antibodies. Western immunoblots revealed that three out of ten samp les 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 appearan ce of TBP antibodies, HPD samples were collected over time from CAPD p atients whose HPD samples taken immediately after catheter insertion l acked anti-TBP antibodies. In two of these patients, each of whom expe rienced an episode of peritonitis due to S. epidermidis or Staphylococ cus hominis, antibodies to the TBP appeared in the HPD collected immed iately post-infection. To determine whether such TBP antibodies were c apable of blocking interactions between transferrin and its staphyloco ccal receptor, HPD immunoglobulin fractions were purified using protei n A-Sepharose beads. In competition assays, these immunoglobulins bloc ked the binding of I-125-labelled transferrin both to whole bacteria a nd to the isolated 42 kDa TBPs of S. aureus and S. epidermidis. These provide evidence to show that staphylococcal TBPs are expressed in viv o during infection.