A genus of lactic acid bacteria of the phylum Firmicutes. Enterococci are Gram-positive cocci that often occur in pairs (diplococci) or short chains and are difficult to distinguish from Streptococci on physical characteristics alone. Two species are common commensal organisms in the intestines of humans: E. faecalis (90-95%) and E. faecium (5-10%). There are rare clusters of infections with other species including E. casseliflavus, E. raffinosus.