Enterococci, one of the most common causes of hospital-associated infections, are responsible for substantial morbidity and mortality. Enterococcus faecalis, the more common and virulent species, causes serious high-inoculum infections, namely infective endocarditis, that are associated with cardiac surgery and mortality rates that remained unchanged for the last 30 years. The best cures for these infections are observed with combination antibiotic therapy; however, optimal treatment has not been fully elucidated. It is the purpose of this review to highlight treatment options and their limitations, and provide direction for future investigative efforts to aid in the treatment of these severe infections. While ampicillin plus ceftriaxone has emerged as a preferred treatment option, mortality rates continue to be high, and from a safety standpoint, ceftriaxone, unlike other cephalosporins, promotes colonization with vancomycin resistant-enterococci due to high biliary concentrations. More research is needed to improve patient outcomes from this high-mortality disease.Keywords. Enterococcus faecalis; infective endocarditis; antimicrobials. , and ability to form biofilm at higher rates than E. faecium (87%-95% vs 16%-29%, respectively) [4,5], makes treatment of E. faecalis infections particularly challenging and may contribute to the unchanging mortality rates. Consequently, combination antimicrobial therapy is required for deep-seated E. faecalis infections, and with >50% of isolates expressing aminoglycoside resistance, treatment options are becoming limited [6]. It is the purpose of this review to highlight available treatment options and their limitations and to provide direction for investigation of future novel combination therapies, including ampicillin plus non-ceftriaxone β-lactams and daptomycin combination therapy, to further aid in the treatment of E. faecalis IE. METHODSStudies were identified by conducting PubMed and Embase searches using the following keywords in 1 or more combinations with "Enterococcus faecalis ": infective, endocarditis, bacteremia, bloodstream, infection, treatment, guideline, antibiotic, combination, synergy, resistant, biofilm, clinical, diagnosis, epidemiology, in vitro, in vivo, simulated endocardial vegetation, experimental, and β-lactamase. Manual searches of reference lists of relevant articles found from initial searches were also conducted. No limitation was placed on publication time period. Studies were selected based on authors' (M. B. and M. K. L.) judgment of relevance to topic. ORIGIN OF COMBINATION THERAPYFor serious E. faecalis infections, such as IE, bactericidal agents, often as combination therapy, are preferred [2]. β-Lactam antibiotics lack bactericidal activity against enterococci when used as monotherapy, making treatment of systemic infections

The combination of vancomycin plus piperacillin-tazobactam increased the odds of acute kidney injury over vancomycin monotherapy, vancomycin plus cefepime or carbapenem, and piperacillin-tazobactam monotherapy. Limited data in critically ill patients suggest the odds of acute kidney injury are increased versus vancomycin monotherapy, and mitigated versus the other comparators. Further research in the critically ill population is needed.

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