Final answer:
Possible reasons for the failure of intravenous chemotherapy and the potential advantages of oral antibiotic therapy.
Step-by-step explanation:
The possible reasons why intravenous chemotherapy failed to completely cure the patient despite laboratory tests showing the bacterial strain was susceptible to the prescribed antibiotic could be attributed to factors such as poor penetration of the antibiotic into the infected tissue, presence of biofilms that protect the bacteria, or development of antibiotic resistance. The second round of antibiotic therapy may have been more successful because oral antibiotics can reach higher concentrations in the infected tissue compared to intravenous antibiotics, and removing the intravenous catheter helps eliminate a potential source of reinfection.