Enterococci are gram-positive bacteria that are widely found in all types of animals and in the environment. They are ubiquitous members of the commensal microbiota and are typically harmless inhabitants of various body sites—particularly the intestinal tract. However, enterococci are opportunistic pathogens that can cause a wide range of signs if the circumstances are advantageous.
Although enterococci are relatively easy to isolate, determination of clinical relevance may be a challenge. In addition, enterococci are inherently resistant to many antimicrobials, including penicillin, clindamycin, trimethoprim–sulfamethoxazole, and low levels of aminoglycosides, and they are poorly responsive to cephalosporins and fluoroquinolones in vivo.