Enterococcus and endocarditis

Infective endocarditis (IE) is a huge topic. The IDSA guidelines are very comprehensive and cover the treatment of IE based on microbiology and valve involved (mechanical vs bioprosthetic). These are linked below.

Enterococcus fecaelis and fecium were given their name to emphasize their presence in the human gastrointestinal tract. There are multiple species of enterococcus, but these two tend to be the most clinically relevant bugs. In the 1930's, the Lancefield classification placed enterococcus in group D, along with strep gallolyticum. Enterococcus was identified as a cause for IE as ealy as 1906, and over the following decades found to cause urinary tract infections, biliary infections, peurperal sepsis, and wound infections during WWI. 

Infective endocarditis is caused by enterococcus in 5-15% of cases. The virulence of this organism is much lower compared to other organisms (ie. S. aureus). Two studies from the 1980's found that bacteremia from enterococcus had a relatively low likelihood of developing endocarditis, where only 2.5% of those with positive blood cultures met criteria. E. fecaelis is more common than E. fecium, which often requires vancomycin therapy given penicillin resistance. Even less frequent than this is vancomycin resistant enterococcus as a cause for endocarditis.  Enterococcal endocarditis is more common in men and older patients, where the average age in one study was 65.  One study from the archives on internal medicine showed that 50% of cases in men followed urinary tract instrumentation, an important risk factor that was present in our case discussion. Other associations include a history of malignancy and nosocomial acquisition. Below is a relatively recent retroprospective database from the American Jounral of Medicine.

Anecdotally, enterococcal endocarditis is less commonly associated with peripheral stigmata, which were absent in our patient. The disease course tends to be subacute with aortic valve involvement being most common.  

Unfortunately, enterococci are less susceptible to beta-lactam antibiotics and synergy with aminoglycosides are often employed. The purpose of dual therapy is to have cell wall breakdown from the penicillin antibiotic allow for improved penetration of the aminoglycosides, which act intra-cellularly on ribosomal activity. Different strains can have varying susceptibility to these antibiotics, which may influence dosing and antibiotics choice. Gentamicin/streptomycin have toxic effects, including ototoxicity and nephrotoxocity and the minimum six weeks of antibiotics required for this diagnosis can lead to significant morbidity. Prosthetic valve endocarditis may fail to be effectively treated with antimicrobials alone, and often requires surgical opinion. I would also advocate for the involvement of the ID service to help with antibiotic choice, dose, interval and duration of therapy.

Enterococcal endocarditis 2005

IDSA infective endocarditis guidelines