Antimicrobial Stewardship for the Treatment of Enterococcal Bloodstream and Urinary Tract Infections: Always a Challenging Choice

The members of the Enterococcus species may be not the most frequent but, without any doubts, among the most problematic human pathogens in terms of antimicrobial therapy. Despite the availability of a number of antimicrobial agents, a substantial proportion of patients do not achieve adequate outcomes, in part because of an increase in the proportion of enterococcal strains that are resistant to 1 or more of these agents. Enterococci can cause a variety of infections. However, for many of these, other pathogens are also frequently isolated from the same site. In such situations, it is often difficult to interpret whether the clinical manifestations of infection are the result of enterococci or whether these lowvirulence bacteria are not playing a significant role in the infection. However, for some types of infections, most notably bloodstream infections and urinary tract infections (EUTIs), enterococci can clearly cause serious disease that needs administration of specific antienterococcal therapies. In this issue of the journal, Taimur et al reviewed retrospective data on patients hospitalized with enterococcal bloodstream infections (EBSIs) and EUTIs during 2008 to 2009 in a single 508-bed academic Boston medical center. Their results demonstrated that vancomycin was commonly used for both empiric and targeted therapy; vancomycin-resistant enterococci were frequent and empiric therapy was inadequate in most of those cases. At the same time, targeted therapy for both EBSI and EUTI was often not tailored to more appropriate agents. The authors concluded that, in such situation, there are many stewardship opportunities to improve prescribing for enterococcal treatment (mainly by using linezolid or daptomycin instead of vancomycin). When we are thinking about antimicrobial stewardship in the case of infection caused by a particular pathogen, we need to know the answers on the following questions: 1.What is the role of the pathogen in the particular infection (in our case, EBSI and EUTI)? In the past decade, Enterococcus species has become the third most common etiological agent isolated in nosocomial bloodstream infections in the United States. However, the rates of isolation of this pathogen from the blood seem to vary significantly in different countries and hospitals. Regarding EUTIs, in the 7-year (2006–2007) retrospective analysis done by Sorlozano et al, enterococci accounted for 18% of 31,758 uropathogens, which were isolated from hospitalized patients in Spain. 2. If there are any significant risk factors for the pathogen? Risk factors for enterococcal infections are not really specific and include the previous use of broad-spectrum antimicrobial, prolonged hospital stay, immunosuppression, serious comorbid conditions, and invasive procedures. The same risk factors are common for a variety of other opportunistic pathogens. 3. What are the resistance rates? The main problem that clinicians are facing in the treatment of enterococcal infections is that these bacteria are not only intrinsically nonsusceptible to many classes of antimicrobials but also have the ability to acquire resistance to all antimicrobials available. Notably, there is a substantial difference between the potential to develop resistance between 2 most clinically significant members of the Enterococcus genus—Enterococcus faecalis (E. faecalis) and Enterococcus faecium (E. faecium). The most clinically important fact is that E. faecalis in most cases remains susceptible to ampicillin where E. faecium is usually resistant to β-lactams. This fact could be very useful for early targeting therapy choice on the basis of the result of identification to the species level. For a long time, the main drug for the management of enterococcal infections resistant to β-lactams was vancomycin.