**3. Identification of enterococci**

Standard textbooks of Bacteriology suggest identification of enterococci by the following characteristics.

Gram positive catalase negative diplococci with growth on MacConkey bile salt lactose agar to distinguish from Streptococci, fermentation of Aesculin on nutrient agar with 4% bile, production of acetoin (Voges-Proskauer test) and the pyrrolidonyl peptidase positive test (PYR) to distinguish from other Group D streptococci, known as non-enterococcal Group D streptococci (Group B streptococci grow on Mac Conkey agar unlike other streptococci and Group A streptococci are also PYR test positive, while all other streptococci are negative) [5].

Enterococci are also hardier than streptococci, the main differences being:

*Enterococcal Infections: Recent Nomenclature and Emerging Trends DOI: http://dx.doi.org/10.5772/intechopen.104792*


Above tests are done only after Lancefield grouping for Group D.

However, *E. faecalis* and *E. faecium* constitute the majority of human enterococcal infections. *E. faecalis* is distinguished from other enterococci by its ability to ferment pyruvate and *E. faecium* by its ability to ferment arabinose [6].

The 16S rRNA typing studied by Gilmore et al. 2013 gave rise to a phylogenetic tree. In 2017, further advances in genetic analysis led to genomic sequence mapping [7, 8]. This study was very interesting in that it traced the origin of enterococci from the pre-historical age and shows their relation to the modern evolved strains isolated from hospital associated infections, including Vancomycin resistant *E. faecium*. They found that enterococcal genome size variation is large ranging from 2.4 to 5.4 Mb. There are 1037 core genes that occur in all enterococci. The human adapted enterococci differed from others (like *Vagococcus lutrae*) in having 126 extra genes that encode for cell wall modifications and de novo Purine biosynthesis, associated with stress response. *E. faecalis* showed resistance to desiccation and *E. faecium* showed resistance to starvation, which may be the result of the gain of new genes. Enterococci are seen in most species from fish to mammals and birds, evolving to find a place in the gut of most animals. Enterococci, they found was the source of all kinds of resistance and virulence factors for other species as well, e.g. the Vancomycin resistance of *S. aureus* is transferred from *E. faecium* [8].
