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.