Enterococci are catalase-negative gram-positive cocci occurring singly, in pairs, or in chains; cells can be ovoid to coccobacillary. There are over twenty species in the genus, categorized within five major groups. Enterococcus faecalis is the most frequently isolated species; Enterococcus faecium, although less frequently encountered, is a significant pathogen.
The Enterococci are widespread in nature; in humans they primarily colonize the gastrointestinal tract but are also found in the genitourinary tract. Enterococci are frequently encountered in urinary tract infections; they are also isolated from wound infections and blood cultures. They are also an important cause of endocarditis.