This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
The test used for the rapid diagnosis of S.aureus infection is: 
Select and explain. 
A. Culture, B. PCR-based assays, C. Serological tests, D. ELISA
B: PCR-based assays
Answer: B: PCR-based assays 
Explanation: Diagnosis of S. aureus infection: Staphylococcal infections are readily diagnosed by Gram's stain Routine culture of infected material usually yields positive results Blood cultures are sometimes positive even when infections are localized to extravascular sites. Polymerase chain reaction (PCR)-based assays have been applied to the rapid diagnosis of S. aureus infection ALSO KNOW: Serologic assays have not proved useful for the diagnosis of staphylococcal infections. Uniformly positive blood cultures suggest an endovascular infection such as endocarditis. Ref: Harrison, Edition-18, Page-1161.