<prompt> An enterococcus E. faecium was isolated from a urine specimen 100,000 cfumL. Treatment of the patient with ampicillin and gentamicin failed. The most clinically appropriate action isDo no further clinical workupSuggest to the laboratory that low colony counts may reflect infectionDetermine if fluorescent microscopy is available for the diagnosis of actinomycosisConsider vancomycin as an alternative drug  <response>: 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. 