Enterococcus

The salt tolerance test separates enterococci, which grow in hypertonic saline, from Streptococcus gallolyticus (bovis), which does not, although both grow in bile. Enterococci are hardy and persist on hospital surfaces, contributing to nosocomial spread. Clinically they cause urinary tract infection, especially after instrumentation, intra-abdominal and biliary sepsis, and endocarditis following genitourinary or gastrointestinal procedures, classically subacute and on abnormal valves. Their resistance profile is examinable: they are intrinsically resistant to cephalosporins and to aminoglycosides as monotherapy, though a cell-wall agent plus an aminoglycoside is synergistic and is the classical regimen for enterococcal endocarditis; E. faecium is far more likely than E. faecalis to be both ampicillin- and vancomycin-resistant. Vancomycin resistance arises from vanA or vanB genes altering the peptidoglycan terminus, and treatment of VRE relies on linezolid or daptomycin. Ampicillin plus ceftriaxone is now an accepted synergistic alternative for E. faecalis endocarditis, avoiding aminoglycoside nephrotoxicity.