Combination Therapy with Ampicillin and Daptomycin for Treatment of Enterococcus faecalis Endocarditis

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f Daptomycin (DAP) is a lipopeptide antibiotic frequently used as a "last-resort" antibiotic against vancomycin-resistant Enterococcus faecium (VRE). However, an important limitation for DAP therapy against VRE is the emergence of resistance during therapy. Mutations in regulatory systems involved in cell envelope homeostasis are postulated to be important mediators of DAP resistance in E. faecium. Thus, in order to gain insights into the genetic bases of DAP resistance in E. faecium, we investigated the presence of changes in 43 predicted proteins previously associated with DAP resistance in enterococci and staphylococci using the genomes of 19 E. faecium with different DAP MICs (range, 3 to 48 g/ml). Bodipy-DAP (BDP-DAP) binding to the cell membrane assays and time-kill curves (DAP alone and with ampicillin) were performed. Genetic changes involving two major pathways were identified: (i) LiaFSR, a regulatory system associated with the cell envelope stress response, and (ii) YycFGHIJ, a system involved in the regulation of cell wall homeostasis. Thr120¡Ala and Trp73¡Cys substitutions in LiaS and LiaR, respectively, were the most common changes identified. DAP bactericidal activity was abolished in the presence of liaFSR or yycFGHIJ mutations regardless of the DAP MIC and was restored in the presence of ampicillin, but only in representatives of the LiaFSR pathway. Reduced binding of BDP-DAP to the cell surface was the predominant finding correlating with resistance in isolates with DAP MICs above the susceptibility breakpoint. Our findings suggest that genotypic information may be crucial to predict response to DAP plus ␤-lactam combinations and continue to question the DAP breakpoint of 4 g/ml.T he surge of Enterococcus faecium as an important nosocomial pathogen has been associated with an expanding pandemic caused by a hospital-associated (HA) genetic clade (1, 2). Indeed, isolates belonging to this genetic lineage are frequently multidrug resistant (MDR) with high MICs of ampicillin and vancomycin (3). Daptomycin (DAP) is a cell membrane (CM)-targeting lipopeptide that has in vitro bactericidal activity against MDR E. faecium and, due to the paucity of other bactericidal options, is often used as first-line therapy despite lacking U.S. Food and Drug Administration approval for these organisms. However, one of the major problems when using DAP against enterococci is the emergence of resistance during therapy (4-6).The mechanisms of DAP resistance in enterococci are not fully understood, but recent evidence suggests that there are several genetic pathways involved and that resistance results from a sequential and ordered mutational pathway (7-9). In Enterococcus faecalis, we have previously shown that emergence of resistance during therapy involves substitutions in three proteins: (i) LiaF, a member of the three-component regulatory system LiaFSR which, in Bacillus subtilis and other Gram-positive bacteria (10), has been shown to orchestrate the cell envelope response to stress; (ii) GdpD, a glycerophosphory...

Section: Resultsmentioning

confidence: 68%

Section: Discussionmentioning

confidence: 71%

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confidence: 99%

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Whole-Genome Analyses of Enterococcus faecium Isolates with Diverse Daptomycin MICs

Diaz

Tran

Munita

et al. 2014

127

175

“…Ampicillin has been shown in several studies to enhance the activity of daptomycin against daptomycin-susceptible isolates (33)(34)(35)(36)(37). Furthermore, a retrospective clinical study demonstrated that the addition of ␤-lactam to daptomycin significantly improved treatment outcomes for vancomycin-resistant Enterococcus (VRE) bloodstream infections when the daptomycin MIC was 4 g/ml (38), and several cases have had successful outcomes resulting from the addition of ampicillin to the treatment regimen for patients failing daptomycin therapy (8,15,17,39).…”

Section: Discussionmentioning

confidence: 99%

In Vitro Activity of Daptomycin in Combination with β-Lactams, Gentamicin, Rifampin, and Tigecycline against Daptomycin-Nonsusceptible Enterococci

Wong-Beringer

Charlton

Miller

et al. 2015

f Enterococci that are nonsusceptible (NS; MIC > 4 g/ml) to daptomycin are an emerging clinical concern. The synergistic combination of daptomycin plus beta-lactams has been shown to be effective against vancomycin-resistant Enterococcus (VRE) species in vitro. This study systematically evaluated by in vitro time-kill studies the effect of daptomycin in combination with ampicillin, cefazolin, ceftriaxone, ceftaroline, ertapenem, gentamicin, tigecycline, and rifampin, for a collection of 9 daptomycin-NS enterococci that exhibited a broad range of MICs and different resistance-conferring mutations. We found that ampicillin plus daptomycin yielded the most consistent synergy but did so only for isolates with mutations to the liaFSR system. Daptomycin binding was found to be enhanced by ampicillin in a representative isolate with such mutations but not for an isolate with mutation to the yycFGHIJ system. In contrast, ampicillin enhanced the killing of the LL-37 human antimicrobial peptide against daptomycin-NS E. faecium with either the liaFSR or yycFGHIJ mutation. Antagonism was noted only for rifampin and tigecycline and only for 2 or 3 isolates. These data add support to the growing body of evidence indicating that therapy combining daptomycin and ampicillin may be helpful in eradicating refractory VRE infections. Daptomycin is a cyclic lipopeptide antimicrobial agent with bactericidal activity against Gram-positive bacteria, including Enterococcus spp. Daptomycin is not approved by the U.S. Food and Drug Administration (FDA) for the treatment of infections caused by vancomycin-resistant Enterococcus (VRE) strains (e.g., vancomycin-resistant Enterococcus faecalis) or by vancomycin-susceptible or -resistant E. faecium strains. However, due to a limited number of available therapeutic options, daptomycin is frequently used in clinical practice for treatment of serious infections caused by these bacteria. No daptomycin resistance breakpoint has been established for the enterococci by the Clinical and Laboratory Standards Institute or the U.S. FDA. Isolates with MICs above the susceptible breakpoint of 4 g/ml are therefore referred to as daptomycin-nonsusceptible (DNS) isolates (1). The prevalence of DNS Enterococcus strains in the United States remains low, ranging from 0.02% for E. faecalis to 0.18% for E. faecium (2). Nonetheless, we and others have isolated DNS Enterococcus strains from both patients treated with and patients naive to daptomycin therapy (3-8) and much higher rates of DNS E. faecium have been reported in Europe (9).The recent description of daptomycin-susceptible Enterococcus strains for which daptomycin exhibits only bacteriostatic activity (10, 11) brings further into question the role of daptomycin for the treatment of enterococcal infections. These isolates have decreased susceptibility to daptomycin (DSD), with daptomycin MICs ranging from 3 to 4 g/ml, which is higher than the wildtype modal daptomycin MICs of 0.5 g/ml for E. faecalis and 2.0 g/ml for E. faecium (12). These isolates harbor po...

“…Two of these studies also demonstrated that AMP and CPT restore not only DAP activity but also endogenous, cationic antimicrobial peptide activity, demonstrating that the effect ␤-lactams have on membrane charge may be imperative for the synergistic effect (24,25). Case reports have also demonstrated the clinical efficacy of the DAP-AMP and DAP-CPT combinations against E. faecalis and E. faecium (24,26,27). Citation Smith JR, Barber KE, Raut A, Rybak MJ.…”

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confidence: 99%

β-Lactams Enhance Daptomycin Activity against Vancomycin-Resistant Enterococcus faecalis and Enterococcus faecium in In Vitro Pharmacokinetic/Pharmacodynamic Models

Smith

Barber

Raut

et al. 2015

Enterococcus faecalis and Enterococcus faecium are frequently resistant to vancomycin and ␤-lactams. In enterococcal infections with reduced glycopeptide susceptibility, combination therapy is often administered. Our objective was to conduct pharmacokinetic/pharmacodynamic (PK/PD) models to evaluate ␤-lactam synergy with daptomycin (DAP) against resistant enterococci. One E. faecalis strain (R6981) and two E. faecium strains (R6370 and 8019) were evaluated. DAP MICs were obtained. All strains were evaluated for response to LL37, an antimicrobial peptide, in the presence and absence of ceftaroline (CPT), ertapenem (ERT), and ampicillin (AMP). After 96 h, in vitro models were run simulating 10 mg DAP/kg body weight/day, 600 mg CPT every 8 h (q8h), 2 g AMP q4h, and 1 g ERT q24h, both alone and in combination against all strains. DAP MICs were 2, 4, and 4 g/ml for strains R6981, R6370, and 8019, respectively. PK/PD models demonstrated bactericidal activity with DAP-CPT, DAP-AMP, and DAP-ERT combinations against strain 8019 (P < 0.001 and log 10 CFU/ml reduction of >2 compared to any single agent). Against strains R6981 and R6370, the DAP-AMP combination demonstrated enhancement against R6370 but not R6981, while the combinations of DAP-CPT and DAP-ERT were bactericidal, demonstrated enhancement, and were statistically superior to all other regimens at 96 h (P < 0.001) against both strains. CPT, ERT, and AMP similarly augmented LL37 killing against strain 8019. In strains R6981 and R6370, CPT and ERT aided LL37 more than AMP (P < 0.001). Compared to DAP alone, combination regimens provide better killing and prevent resistance. Clinical research involving DAP combinations is warranted. Enterococcus faecalis and Enterococcus faecium together account for 12% of hospital-acquired infections in the United States (1). Often, enterococcal infections are caused by multidrug-resistant strains. For example, 0.4 to 5.2% and 70 to 92.6% of E. faecalis and E. faecium strains are resistant to ampicillin, respectively, and vancomycin resistance is present in up to 12.5% of E. faecalis and 79.7% of E. faecium (2-4). Vancomycin-resistant enterococci (VRE) are associated with increased mortality and complicated infections, such as infective endocarditis (5). Treatment of VRE infections can prove problematic, as available treatment options are potentially limited by static activity and/or platelet suppression with long-term use (6-8). Daptomycin (DAP) is a bactericidal lipopeptide often used against resistant enterococci (9). Mechanistically, it binds with calcium to form a cationic moiety that disrupts membrane potential to confer its antimicrobial effects, similar to endogenous, cationic antimicrobial peptides (10, 11). DAP is frequently dosed at 6 mg/kg body weight daily, although recent clinical and in vitro data suggest improved efficacy at higher doses (7,(12)(13)(14). DAP retains excellent in vitro activity against E. faecalis and E. faecium, with MIC 50/90 values of 1/2 and 2/4 g/ml, respectively (15). Reports of DAP-nonsuscept...