Ampicillin-resistant and vancomycin-susceptible Enterococcus faecium bacteremia: a clinical narrative review

ABSTRACT

Introduction

Enterococcus faecium is a commensal microorganism that can cause infections such as bacteremia. Incidence of ampicillin-resistant and vancomycin-susceptible E. faecium (EfARSV) bacteremia is on the rise, and the mortality rate is high. Despite much data, the most appropriate treatment remains a question.

Areas covered

This article mostly reviews the relevant aspects of EfARSV bacteremia: microbiology, gastrointestinal tract colonization and invasion, antibiotic resistance, epidemiology, risk factors, mortality, and treatment, including pharmacologic components of employed agents and related clinical evidence. A literature search was conducted on PubMed on 31 July 2022, which was updated on 15 November 2022.

Expert opinion

EfARSV bacteremia presents high mortality. However, it is uncertain whether mortality is attributable to or a marker of severity/comorbidities. Considering its antibiotic resistance pattern, EfARSV is considered a difficult-to-treat microorganism. Glycopeptides have been used to treat EfARSV, with linezolid and daptomycin serving as potential alternative agents. Yet, the use of daptomycin is controversial due to a higher risk of treatment failures. Clinical evidence on this issue is scarce, unfortunately, and subject to many limitations. Despite increased incidence and mortality, EfARSV bacteremia presents multiple aspects to be addressed in well-conducted studies.

KEYWORDS:

• Bacteremia
• bloodstream infection
• daptomycin
• Enterococcus faecium
• linezolid
• oritavancin
• teicoplanin
• vancomycin

Article highlights

• Incidence of infections caused by Enterococcus faecium is increasing, especially bacteremia, which is related to high morbidity and mortality.

• Although E. faecalis bacteremia has been historically predominant, E. faecium has become more prevalent. This finding raises concerns, as E. faecium bacteremia exhibits higher mortality.

• Several reasons may explain this increase:

  1. Both its extraordinary ability to survive hostile environments and its antibiotic resistance, which confers an important selective advantage.

  2. A rise in the number of patients with risk factors and antibiotic pressure, which predisposes them to infection.

• Risk factors are well-known: comorbidities (advanced age, diabetes, immunosuppression); admission to ICU; broad-spectrum antibiotics (especially third generation cephalosporins and carbapenems); prolonged hospital stay or the use of urinary/vascular catheters.

• Mortality remains high, although it is uncertain whether it is attributable to either the infection or a marker of severity/comorbidities.

• Ampicillin-resistant and vancomycin-susceptible E. faecium is considered a difficult-to-treat microorganism. Physicians face the challenge of balancing varying considerations, including patients’ comorbidities, infection severity and the high propensity for antibiotic-related toxicities.

• Glycopeptides, linezolid and daptomycin remain the most employed antibiotic agents.

• Clinical evidence is scarce and low-quality. Glycopeptides and linezolid are first-line agents. The use of daptomycin is controversial due to concerns of a higher risk of treatment failure.

• Other significant aspects remain unresolved, including the importance of appropriate empiric treatment, length of treatment and oral switch.

• Randomized controlled clinical trials are needed to determine the most appropriate treatment.

Acknowledgments

We would like to thank Anthony Armenta for providing medical editing assistance for the article at hand.

Declaration of interest

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants, patents received or pending, or royalties.

Reviewers Disclosure

Peer reviewers on this manuscript have no relevant financial relationships or otherwise to disclose.

Additional information

Funding

This paper was not funded.