Is Enterococcus Associated with Endocarditis?
Yes, Enterococcus is definitively associated with endocarditis and represents one of the three most common causative organisms of infective endocarditis worldwide, alongside staphylococci and streptococci. 1
Epidemiology and Clinical Significance
Enterococci cause 5-20% of all infective endocarditis cases, with Enterococcus faecalis and E. faecium being the predominant species isolated from clinical sources 1, 2, 3
In prosthetic valve endocarditis specifically, enterococci are among the most frequent organisms in late-onset disease (>1 year post-surgery), where the microbial spectrum mirrors native valve endocarditis 1
Enterococcal endocarditis typically affects an older, more comorbid population compared to other forms of endocarditis, with patients frequently over 65 years of age and having chronic underlying diseases 4, 5
Clinical Characteristics
The genitourinary tract is the most common source of infection, with 30% of cases having preceding urinary tract infections 4, 3
The disease typically presents in a subacute fashion rather than the acute, fulminant presentation seen with Staphylococcus aureus endocarditis 1, 3
Enterococcal endocarditis produces fewer peripheral vascular manifestations and immunological phenomena (14.5% vs 27.1% for non-enterococcal cases) compared to other bacterial causes 4
Both normal and previously damaged valves can be affected, though calcified valves are more commonly involved (18.6% of cases) 4, 3
Mortality and Prognosis
In-hospital mortality for enterococcal endocarditis is approximately 33%, which is significantly higher than viridans group streptococci (9.3%) but lower than S. aureus endocarditis (48.6%) 4
The relapse rate is higher than non-enterococcal endocarditis (6.6% vs 2.3%), necessitating prolonged treatment courses 4, 5
Approximately 37% of patients require valve surgery during hospitalization to achieve cure 4
Treatment Considerations
Enterococci require synergistic combination therapy because they are relatively resistant to penicillin, ampicillin, and vancomycin as monotherapy—these agents inhibit but do not kill enterococci 1
The synergistic combination of a cell wall-active agent (penicillin, ampicillin, or vancomycin) plus an aminoglycoside (gentamicin or streptomycin) is required to achieve bactericidal activity 1, 3
All enterococcal isolates should be routinely tested for susceptibility to penicillin and vancomycin (MIC determination) and for high-level resistance to gentamicin and streptomycin (Class I, Level of Evidence: A) 1
High-level aminoglycoside resistance (HLAR) is emerging, detected in approximately 13% of cases, which necessitates alternative regimens such as ampicillin plus ceftriaxone 2, 4
Key Clinical Pitfall
The most critical error is treating enterococcal endocarditis with monotherapy—enterococci are inherently resistant to killing by single agents due to their relative impermeability to aminoglycosides and tolerance to cell wall-active agents alone 1, 6, 5. Cell wall-active agents increase enterococcal permeability, allowing aminoglycosides to reach intracellular ribosomal targets and achieve bactericidal synergy 1.