First, a vancomycin MIC test should be used to confirm that the organism is vancomycin resistant. Testing for ampicillin resistance simultaneously using MIC or disk diffusion can also be useful since ampicillin resistant strains are almost always E. faecium . Second, there are three tests that can be used to rule out intrinsic vancomycin resistant species, i.e., E. gallinarum and E. casseliflavus . These tests will differentiate intrinsic vancomycin resistant species from E. faecalis and E. faecium . Pigment is determined by touching colonies with a cotton-tipped swab and examining the cotton tip for a yellow color.
Motility is best determined using a semi-solid motility medium incubated overnight.
While failure to grow on this medium will rule out VRE, Enterococcus spp. Enterococci with acquired vancomycin resistance typically contain vanA or vanB genes and these genes can be transferred among bacteria. In contrast to isolates with vanA and vanB genes, isolates with vanC have not been associated with nosocomial outbreaks. When we report an isolate as VRE, we are implying that the isolate has acquired vancomycin resistance and infection control interventions are required. The technologist subcultured the isolate to a blood agar plate and set up a semi-solid motility medium tube and an MIC test.