Purpose

Enterococci are Gram positive cocci that normally reside in the intestinal tract and gain vancomycin resistance through the acquisition of the vanA or vanB gene. The two most common species to acquire these resistance mechanisms are Enterococcus faecium and Enterococcus faecalis. The vancomycin resistant enterococci (VRE) screen is used to identify patients who are carriers of VRE and place them in isolation. VRE screens are performed on patients with a history of vancomycin resistant enterococci. Intrinsic resistance to vancomycin (vanC) is common in Enterococcus gallinarum and Enterococcus casseliflavus and is not of interest in the VRE screen as it does not require the patient to be placed in isolation. Resistance of vancomycin by enterococci can also be detected by an increased MIC value >4 ug/mL, or by an intermediate zone size, 15-16 mm, produced by the Kirby Bauer method of susceptibility testing.