This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bacteria, Subject name: Microbiology
An enterococcus (E. faecium) was isolated from a urine specimen (100,000 cfu/mL). Treatment of the patient with ampicillin and gentamicin failed. The most clinically appropriate action is 
Select and explain. 
A. Do no further clinical workup, B. Suggest to the laboratory that low colony counts may reflect infection, C. Determine if fluorescent microscopy is available for the diagnosis of actinomycosis, D. Consider vancomycin as an alternative drug
D: Consider vancomycin as an alternative drug
Answer: D: Consider vancomycin as an alternative drug 
Explanation: These questions demonstrate commonly occurring clinical infectious diseases and microbiologic problems. Enterococci may be resistant to ampicillin and gentamicin. Vancomycin would be the drug of choice. However, laboratory results do not always correlate well with clinical response. The National Committee on Clinical Laboratory Standards recommends testing enterococci only for ampicillin and vancomycin.