Enterococci are gram-positive cocci that are observed as single cells, diplococci, or short chains.

• Enterococci share many morphologic and phenotypic characteristics with streptococci and thus were previously classified as the latter.
• Enterococci are generally nonhemolytic when cultured on blood agar plates.
• Enterococci are inherently resistant to a variety of commonly used antibiotics. E. faecium is the most resistant species, with >80% of US isolates resistant to vancomycin (VRE) and >90% resistant to ampicillin. In contrast, only ~7% of E. faecalis isolates are resistant to vancomycin and ~4% to ampicillin.