Since the early 1970s, the enterococci have steadily emerged as major hospital-acquired (nosocomial) pathogens. In statistics from the National Nosocomial Infectious Surveillance System (NNISS), they are the second most common gram-positive cause of nosocomial bloodstream infection and the third most common cause of nosocomial wound infections. In fact, enterococci rank first among gram-positive cocci in producing urinary tract infections (17.4%, see Table 133.1). The significant increases in occurence of this genus since the early to mid-1970s is related to patterns of general antimicrobial use in the hospital and in particular to widespread use of extended-spectrum cephalosporins, β-lactamase inhibitor/penicillin combinations, fluoroquinolones, carbapenems, and aminoglycosides and the emergence of resistances in the genus.

Cephalosporins are not active or bactericidal against enterococci, and they may therefore result in a selective advantage for this genus. Fluoroquinolones are also only modestly active against these species. Enterococcus faecalis produce most human enterococcal infections (70% to 80%), and Enterococcus faecium accounts for most (10% to 16%) of the remainder. Antimicrobial resistance is a particular problem among E. faecium isolates. Other species of interest are Enterococcus casseliflavus and Enterococcus gallinarum, not because of the frequency with which they are isolated, but because of the intrinsic low-level resistance to vancomycin (eg, the vanC genotype and resultant generally intermediate phenotype; minimum inhibitory concentrations [MICs], 4–8 μg/mL).