Final answer:
The negative blood cultures in an immunocompromised patient with a Gardnerella vaginalis infection can be attributed to the presence of sodium polyanethol sulfonate (SPS) in the blood culture media. Removing the intravenous catheter and administering oral antibiotics may have contributed to the success of the second round of antibiotic therapy.
Step-by-step explanation:
The discrepancy between the negative blood cultures after 5 days of incubation and the presence of fever spikes in the immunocompromised patient with Gardnerella vaginalis infection can be explained by the presence of sodium polyanethol sulfonate (SPS) in the blood culture media. SPS is an anticoagulant that can inhibit the growth of certain bacteria, including Gardnerella vaginalis. Therefore, the SPS in the blood culture media may have prevented the growth of the organism and resulted in negative blood cultures.
The second round of antibiotic therapy may have been more successful because the intravenous catheter, which was a potential source of infection, was removed. By removing the source of infection, the patient's immune system and the oral antibiotics could effectively target and eliminate the remaining infection.