A 67 Year Old man with Fever After a prosthetic aortic valve replacement...

A 67-year-old man presents with a  6-week history of malaise, low-grade pyrexia and rigors 6 months after having a prosthetic aortic valve replacement.
His C-reactive protein is 150 mg/dL (normal <5 mg/dL) and
his creatinine 150 μmol/L (normal <120 μmol/L).
 A transoesophageal echocardiogram confirms vegetation on the aortic prosthesis.

Question
Which of the following organisms is most likely to be responsible?

A Staphylococcus aureus
B Streptococcus viridans
C Staphylococcus epidermidis
D Escherichia coli
E Candida albicans

Answer:
C Staphylococcus epidermidis

Discussion: Although streptococci are the most common cause of native valve endocarditis, postoperatively staphylococci are most likely and the history is suggestive of Staphylococcus epidermidis.
Staphylococcus aureus is more likely to present in the early postoperative period and follows a more fulminant course.