27
Antimicrobial Therapy of VRE and MRSA
in Critical Care
Burke A. Cunha
Infectious Disease Division, Winthrop-University Hospital, Mineola, New York, and State University
of New York School of Medicine, Stony Brook, New York, U.S.A.INTRODUCTION
Group D Enterococci
Aerobic streptococci are classified via the Lancefield typing system, i.e., group A, B, C, G,
or D streptococci. Group D streptococci may be further subdivided as enterococcal or non-
enterococcal group D streptococci. The most important non-enterococcal group D streptococcus
isStreptococcus gallolyticus(S. bovis), which is ordinarily not an important pathogen in the critical
care setting. Group D enterococci, however, are the predominant streptococcal pathogens
encountered in critical care. Group D enterococci reside in the hepatobiliary and gastrointes-
tinal tracts. Group D enterococci are relatively noninvasive with a pathogenicity
that is intermediate between methicillin-sensitiveStaphylococcus aureus/methicillin-resistant
Staphylococcus aureus(MSSA/MRSA) and coagulase-negative staphylococci (CoNS). Because
group D streptococci colonize the terminal colon, they are frequent colonizers of the urinary
tract. Group D enterococci primarily colonize the hepatobiliary/gastrointestinal tract and are
frequent secondary colonizers of bile, wounds, and urine (1).
The two most important group D enterococcal pathogens areEnterococcus faecalisand
Enterococcus faecium. E. faecalisalmost always is susceptible to vancomycin and so may also be
termed vancomycin-sensitive enterococci (VSE). In contrast,E. faeciumis uniformly resistant to
vancomycin and may be termed vancomycin-resistant enterococci (VRE). As with MSSA/
MRSA, VSE/VRE isolates are equally virulent and have the same clinical spectrum of
infection. The only difference between VSE and VRE, as with MSSA and MRSA, is antibiotic
susceptibility. Unlike with MRSA, in vitro susceptibility to VSE/VRE as with MSSA correlate
with in vivo effectiveness. The clinical spectra of VSE/VRE infections include catheter-
associated bacteriuria (CAB), urinary tract infections (UTIs; cystitis, pyelonephritis), biliary
tract infections (cholecystitis, cholangitis), hepatic infections (copathogen in liver abscesses),
intra-abdominal/pelvic pathogens (copathogen in peritonitis, abscess), central venous catheter
(CVC) infections, and subacute bacterial endocarditis (SBE). Ordinarily VSE/VRE are not
pathogens in CNS infections, pneumonias, skin/soft tissue infections, or bone/joint infections.
Isolation of VSE or VRE as a single pathogen in blood cultures should suggest biliary tract
infection, UTI, or SBE. Group D streptococci, occurring in blood cultures as part of a
polymicrobial infection should suggest a gastrointestinal source. Excluding intravascular and
intra-abdominal infections between the gallbladder and the urinary bladder, group D
enterococci should be regarded as “permissive pathogens.” As mentioned above, VSE/VRE
may be pathogenic alone in infections of the biliary tract, urinary tract, or intravascular
infections. Excluding CVC infections, unlike staphylococci, group D enterococci are rarely, if
ever, associated with device-related infections (1).
Selection of antimicrobial therapy of VSE/VRE infections depends on the susceptibility
of the isolate host factors (allergy history, renal/hepatic function, site of infection, etc.). The
duration of therapy depends on the type/site of infection and varies from one to two weeks for
hepatobiliary or intra-abdominal infections to four to six weeks for SBE. Because group D
enterococci are copathogens in intra-abdominal/pelvic abscesses, surgical drainage is the most
important therapeutic intervention in these infections (1).