This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.N.S, Subject name: Medicine
Most common cause of epidural abscess 
Select and explain. 
A. Staphylococcus, B. Streptococcus, C. Gram negative bacilli, D. Microanerophilic anaerobic streptococci
A: Staphylococcus
Answer: A: Staphylococcus 
Explanation: Harrison's principles of internal medicine. * Staphylococci or gram negative organisms are the usual cause of an epidural abscess