It is extremely difficult to eradicate staphylococcal infection in the presence of a foreign body. Thus, infected artificial joints and infected intravenous lines often must be removed in conjunction with optimal intravenous anti-staphylococcal therapy with oxacillin or nafcillin (sometimes in combination with rifampin) in order to eradicate such staphylococcal infections (and these attempts are not always successful). Staphylococcal infection of bone may persist for many years despite what should be optimal antimicrobial therapy. The most likely reason for this tenacity of staphylococcal osteomyelitis is: A. The Staphylococcal pilus gene is up-regulated by oxacillin B. Fragments of dead bone, called "involucrum" may act as a foreign body, and may have to be removed for optimal eradication of the staphylococcal infection. C. Staphylococci may be perceived by the patient's immune system as a positive factor, because the staphylococci produce an extracellular enzyme, obtundokinase, which makes the patient more alert. D. Staphylococci are such an integral part of our normal flora that they are treated as "self" rather than "non-self", and no immune reaction to them occurs.