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The page below is a sample from the LabCE course Case Studies in Clinical Microbiology. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Enterococcus faecium Identification

  • As a high percentage of Enterococcus faecium strains carry the Van A gene and are highly resistant to vancomycin, species identifications are performed in some laboratories where MIC susceptibility testing may not be available.
  • Methods for the phenotypic separation of E. faecium from E. faecalis are limited.
  • Illustrated in this image are positive reactions for acid production from arabinose and melibiose (yellow color), characteristic of E. faecium. E. faecalis are negative for these reactions.
  • A few preformed substrates, such as beta galactosidase (E. faecium positive, E. faecalis negative), also serve to separate these two species, accomplished by certain commercial systems that include these substrates.
  • E. faecium is not motile, an additional characteristic helpful to separate vancomycin-resistant Enterococcus (VRE) species from E. cassiloflavus and E. gallinarum, both of which are motile, and carry the low level resistant gene VAN-c.