Enterococci are gram-positive facultative anaerobic bacteria and are normal flora of the human gastrointestinal tract. Historically classified as group D streptococci, enterococci are now classified as a separate genus with at least 35 different species.
PATHOGENESIS AND EPIDEMIOLOGY
Only 2 species, Enterococcus faecalis and Enterococcus faecium, account for all but a rare case of human disease. E faecalis is responsible for about 80% to 90% of human cases, but several studies show a rising proportion of cases due to E faecium. Enterococci are facultatively anaerobic catalase-negative gram-positive cocci that normally inhabit the bowel. Approximately half of newborn infants have acquired colonization with enterococci by 1 week of age. These very hardy organisms grow at temperatures of 10°C to 60°C (50–140°F) and remain viable for weeks on environmental surfaces such as bed rails, sinks, faucets, and doorknobs. Human-to-human spread is common in hospital settings.
Enterococci generally are not highly invasive pathogens and typically are classified as opportunists. They lack not only the major exotoxins and endotoxins associated with virulent streptococci and staphylococci, but also the enzymes that enable rapid tissue spread. Infections are most often associated with prolonged hospitalization, particularly in intensive care or hematology/oncology units; use of broad-spectrum antibiotics; indwelling lines; immunocompromised state; or loss of integrity of the gastrointestinal tract, urinary tract, or skin.
The 3 most common types of infection associated with enterococci are urinary tract infection (UTI), polymicrobial abdominal infections, and bacteremia or sepsis. Although infrequent, cases of focal organ infection, such as endocarditis, meningitis, and wound infections, may be severe. UTI caused by enterococci almost never occurs in otherwise healthy children. They are most often associated with indwelling urinary catheters and account for approximately 15% of nosocomial UTIs in children. Anatomic urinary tract anomalies, particularly vesicoureteral reflux, are more common in community-acquired enterococcal UTIs than those associated with gram-negative Enterobacteriaceae.
Enterococci may be involved in intra-abdominal polymicrobial infections following intestinal perforation such as ruptured appendix or necrotizing enterocolitis. Although there has been controversy regarding the pathogenic role of enterococci in such infections, most authorities recommend adding an antibiotic to cover for enterococci in the setting of healthcare-associated intra-abdominal infections, particularly postoperative infections. Empiric therapy also should be considered for severe sepsis of abdominal origin in immunocompromised patients or patients who recently received broad-spectrum antibiotics selecting for Enterococcus species. Enterococcal bacteremia or sepsis in children may not be identified with a specific focus, but common risk factors are use of broad-spectrum antibiotics or intravascular catheters in association with underlying conditions such as surgery, immunosuppression, transplants, or major organ dysfunction. Bacteremia without a focal infection may result in a self-limited illness or a severe and life-threatening illness, particularly in newborns or children with underlying disease. Bacteremia is often polymicrobial with other enteric microorganisms. Mortality occurs in up to 25% of cases but is hard to separate from the ...