Enterococci may be considered an essential part of the autochthonous microflora of humans and animals. Some host specificity exists (Table 7.1). E. faecalis and E. faecium are frequently found in humans. In poultry, cattle, and pigs, E. faecium is common, as well as other species like E. faecalis and E. cecorum. E. cecorum, originally found in poultry intestines, has also been isolated from pigs, cattle, horses, canaries and ducks (Devriese et al., 1991a). E. gallinarum and E. durans/hirae do not occur so often in the intestine of animals and E. avium is a very rare species there. Some species like E. casseliflavus and E. mundtii are found mostly in plants. Colonies of both are pigmented whilst E. gallinarum and E. casseliflavus are motile, indicating a great diversity in physiology and ecology within the genus.