Final answer:
Intravenous antibacterial chemotherapy may not have eradicated the S. epidermidis infection due to biofilm formation on the catheter, among other factors. Oral antibiotics succeeded after removal of the catheter, likely due to different pharmacokinetics and sustained drug levels in the system.
Step-by-step explanation:
Intravenous antibacterial chemotherapy may have failed to cure the patient for several reasons despite the susceptibility of the bacterial strain to the prescribed antibiotic. One possibility is that S. epidermidis formed a biofilm on the surface of the catheter, which can protect bacteria from the effects of antibiotics and the immune system. Additionally, the concentration of the antibiotic may have been insufficient within the biofilm or the local tissue surrounding the catheter to completely eradicate the bacteria. Interruption or inconsistency in the delivery of the antibiotic via intravenous catheter could also have allowed the bacteria to survive and eventually proliferate once the therapy was discontinued.
The second round of oral antibiotics could have been more successful for a few reasons. After removing the catheter, which might have been the source of the persistent infection due to the biofilm, the oral antibiotics provided a new means to maintain sustained therapeutic levels of the drug in the patient's system. Oral antibiotics also have different pharmacokinetics and could result in higher local tissue concentrations that are more effective in eradicating the bacteria.