The enterococci: evidence of species-specific clinical and microbiologic heterogeneity

Investigations of the clinical role of enterococci have been limited largely to enterococcal bacteremia and endocarditis and have not distinguished between the various species of enterococci. To characterize the full spectrum of enterococcal disease and to determine whether clinically important differences exist among infections and/or instances of colonization (infections/colonizations) by the various enterococcal species, cases of enterococcal infection/colonization diagnosed at the Dallas Veterans Administration Medical Center (DVAMC) in 1986 were reviewed. During this period, 220 Enterococcus faecalis, 21 Enterococcus faecium, 12 Enterococcus avium, and no Enterococcus durans isolates were identified in clinical specimens (other than stool) submitted to the DVAMC microbiology laboratory. Clinical characteristics of cases of infection/colonization by the three species of enterococci were similar and did not vary significantly when blood stream invasion occurred. Nevertheless, mortality data and therapeutic response rates suggested differences in virulence of the three enterococcal species. Enterococcal infections/colonizations (including bacteremia) frequently were polymicrobial. Although Enterobacteriaceae were the most common copathogens identified overall, Staphylococcus aureus was the most common copathogen in bloodstream infections. E. avium was more resistant than E. faecalis or E. faecium to penicillin G and ampicillin and less resistant to most other antimicrobial agents. The results of this investigation suggest that enterococci are a heterogeneous group of bacteria that should not be treated as a single entity in clinical investigations.