Influence of Inoculum Effect on the Efficacy of Daptomycin Monotherapy and in Combination with β-Lactams against Daptomycin-Susceptible Enterococcus faecium Harboring LiaSR Substitutions

MtlD as a therapeutic target for intestinal and systemic bacterial infections

The ability to treat infections is threatened by the rapid emergence of antibiotic resistance among pathogenic microbes. Therefore, new antimicrobials are needed. Here we evaluate mannitol-1-phosphate 5-dehydrogenase (MtlD) as a potential new drug target. In many bacteria, mannitol is transported into the cell and phosphorylated by MtlA, the EIICBA component of a phosphoenolpyruvate-dependent sugar phosphotransferase system. MtlD catalyzes the conversion of mannitol-1-phosphate (Mtl-1P) to fructose-6-phosphate, which enters the glycolytic pathway. Mutants lacking mtlD are sensitive to mannitol due to accumulation of Mtl-1P. Here, we constructed mtlD mutants in four different bacterial species (Cronobacter sakazakii, Pseudomonas aeruginosa, five serovars of Salmonella enterica, and three strains of Escherichia coli), confirming and quantifying their mannitol sensitivity. The quantification of mannitol sensitivity in vitro was complicated by an inoculum effect and a resumption of growth following mannitol intoxication. The rate of resumption at different mannitol concentrations and cell population densities is fairly constant and reveals what is likely an intoxication processing rate. Provision of mannitol in drinking water, or by intraperitoneal injection, dramatically attenuates infection of a Salmonella enterica serovar Typhimurium mtlD mutant in mouse models of both gastroenteritis and systemic infection. Using CC003/Unc mice, we find that a mtlD mutant of Salmonella enterica serovar Typhi is also attenuated by provision of mannitol in drinking water. Therefore, we postulate that MtlD could be a valuable new therapeutic target.

IMPORTANCE

The ability to treat infections is threatened by the rapid emergence of antibiotic resistance. Mannitol is a polyol used in human medicine and the food industry. During catabolism of mannitol, many bacteria transport mannitol across the inner membrane forming the toxic intermediate mannitol-1-phosphate (Mtl-1P). Mtl-1P must be processed by mannitol dehydrogenase (MtlD) or it accumulates intracellularly, causing growth attenuation. We test and confirm here that mtlD mutants of Escherichia coli (including UPEC, and EHEC), Salmonella (including serovars Typhi, and Paratyphi A, B, and C), Cronobacter, and Pseudomonas experience mannitol sensitivity in vitro. Furthermore, providing mannitol in drinking water can alleviate both gastrointestinal and systemic Salmonella infections in mice. This suggests that inhibition of MtlD could be a viable antimicrobial strategy.

Phage-antibiotic synergy against daptomycin-nonsusceptible MRSA in an ex vivo simulated endocardial pharmacokinetic/pharmacodynamic model

Phage-antibiotic combinations (PAC) offer a potential solution for treating refractory daptomycin-nonsusceptible (DNS) methicillin-resistant Staphylococcus aureus (MRSA) infections. We examined PAC activity against two well-characterized DNS MRSA strains (C4 and C37) in vitro and ex vivo. PACs comprising daptomycin (DAP) ± ceftaroline (CPT) and a two-phage cocktail (Intesti13 + Sb-1) were evaluated for phage-antibiotic synergy (PAS) against high MRSA inoculum (109 CFU/mL) using (i) modified checkerboards (CB), (ii) 24-h time-kill assays (TKA), and (iii) 168-h ex vivo simulated endocardial vegetation (SEV) models. PAS was defined as a fractional inhibitory concentration ≤0.5 in CB minimum inhibitory concentration (MIC) or a ≥2 log10 CFU/mL reduction compared to the next best regimen in time-kill assays and SEV models. Significant differences between regimens were assessed by analysis of variance with Tukey's post hoc modification (α = 0.05). CB assays revealed PAS with Intesti13 + Sb-1 + DAP ± CPT. In 24-h time-kill assays against C4, Intesti13 + Sb-1 + DAP ± CPT demonstrated synergistic activity (-Δ7.21 and -Δ7.39 log10 CFU/mL, respectively) (P < 0.05 each). Against C37, Intesti13 + Sb-1 + CPT ± DAP was equally effective (-Δ7.14 log10 CFU/mL each) and not significantly different from DAP + Intesti13 + Sb-1 (-Δ6.65 log10 CFU/mL). In 168-h SEV models against C4 and C37, DAP ± CPT + the phage cocktail exerted synergistic activities, significantly reducing bio-burdens to the detection limit [2 log10 CFU/g (-Δ7.07 and -Δ7.11 log10 CFU/g, respectively)] (P < 0.001). At 168 h, both models maintained stable MICs, and no treatment-emergent phage resistance occurred with DAP or DAP + CPT regimens. The two-phage cocktail demonstrated synergistic activity against two DNS MRSA isolates in combination with DAP + CPT in vitro and ex vivo. Further in vivo PAC investigations are needed.

Phage-antibiotic combinations against multidrug-resistant Pseudomonas aeruginosa in in vitro static and dynamic biofilm models

Biofilm-producing Pseudomonas aeruginosa infections pose a severe threat to public health and are responsible for high morbidity and mortality. Phage-antibiotic combinations (PACs) are a promising strategy for combatting multidrug-resistant (MDR), extensively drug-resistant (XDR), and difficult-to-treat P. aeruginosa infections. Ten MDR/XDR P. aeruginosa strains and five P. aeruginosa-specific phages were genetically characterized and evaluated based upon their antibiotic susceptibilities and phage sensitivities. Two selected strains, AR351 (XDR) and I0003-1 (MDR), were treated singly and in combination with either a broad-spectrum or narrow-spectrum phage, phage EM-T3762627-2_AH (EM), or 14207, respectively, and bactericidal antibiotics of five classes in biofilm time-kill analyses. Synergy and/or bactericidal activity was demonstrated with all PACs against one or both drug-resistant P. aeruginosa strains (average reduction: -Δ3.32 log10 CFU/cm2). Slightly improved ciprofloxacin susceptibility was observed in both strains after exposure to phages (EM and 14207) in combination with ciprofloxacin and colistin. Based on phage cocktail optimization with four phages (EM, 14207, E20050-C (EC), and 109), we identified several effective phage-antibiotic cocktails for further analysis in a 4-day pharmacokinetic/pharmacodynamic in vitro biofilm model. Three-phage cocktail, EM + EC + 109, in combination with ciprofloxacin demonstrated the greatest biofilm reduction against AR351 (-Δ4.70 log10 CFU/cm2 from baseline). Of remarkable interest, the addition of phage 109 prevented phage resistance development to EM and EC in the biofilm model. PACs can demonstrate synergy and offer enhanced eradication of biofilm against drug-resistant P. aeruginosa while preventing the emergence of resistance.

Ciprofloxacin in combination with bacteriophage cocktails against multi-drug resistant Pseudomonas aeruginosa in ex vivo simulated endocardial vegetation models

Pseudomonas aeruginosa-associated infective endocarditis represents difficult-to-treat, deep-seated infections. Phage-antibiotic combinations have shown to eradicate multi-drug resistant (MDR) P. aeruginosa, limit the development of phage resistance, and restore antibiotic sensitivity. The objective of this study was to evaluate the activity of phage-ciprofloxacin (CIP) combinations in 4-day ex vivo simulated endocardial vegetation (SEV) models against drug-resistant P. aeruginosa isolates. Two P. aeruginosa isolates, extensively drug-resistant AR351 and MDR I0003-1, were selected for their drug resistance and sensitivity to phage. Three phages [LL-5504721-AH (LL), E2005-C (EC), and 109] and CIP were evaluated alone and in combination for their activity and influence on drug and phage resistance using 24-h time-kill analysis. The three-phage cocktail (q24h) in combination with CIP (400 mg q12h) was then tested in dynamic 4-day ex vivo SEV models, with reduction of log10 CFU/mL compared using ANOVA with Bonferroni analysis. Compared to other combinations, CIP-LL-EC-109 demonstrated synergistic and bactericidal activity from starting CFU/g against AR351 and I0003-1 (-Δ5.65 and 6.60 log10 CFU/g, respectively; P < 0.001). Additionally, CIP-LL-EC-109 mitigated phage resistance, while all other therapies had a high degree of resistance to >1 phages, and all phage-containing regimens prevented CIP mean inhibitory concentration increases compared to CIP alone for both AR351 and I0003-1 at 96 h.

Targeting Dalbavancin Inoculum Effect: Adjunctive Single Dose of Daptomycin

INTRODUCTION

Daptomycin (DAP) has proven to be a viable alternative amid vancomycin resistance; however, the use of DAP post vancomycin treatment has led to the development of DAP non-susceptible (DNS) strains. Dalbavancin (DAL), a novel single-dosed lipoglycopeptide, has shown enhanced activity against highly resistant Staphylococcus aureus strains. However, on the basis of previous reports and our observations, DAL does not demonstrate similar activity at high versus low inoculum levels. Therefore, we hypothesized that addition of DAP even at minimal concentrations (single dose on day 1) will lower the inoculum to the level that can be cleared by dalbavancin.

METHODS

Isolates from methicillin-resistant S. aureus (MRSA)-infected patients with varying susceptibility profiles were evaluated using broth microdilution methods. Two DNS-VISA strains (vancomycin intermediate resistant S. aureus) and one MRSA strain were further evaluated in a one-compartment PK/PD model using a high starting initial inoculum of 109 CFU/mL as well as low initial inoculum of 107 CFU/mL over 168 h to assess the activity of DAL and DAP monotherapy and in combination.

RESULTS

Single therapies were not bactericidal when evaluated in the 168 h in vitro one-compartment model with an initial inoculum of 109; however, the combination of DAL plus single dose of DAP resulted in enhanced killing at the end of the 168-h exposure. DAL single therapy caused reduction in colony counts down to detection limit (2 log10 CFU/ml) at a lower inoculum but did not show enhancement (< 2 log10 CFU/ml) at higher initial inoculums (P < 0.01) for all three strains. Similarly, DAP caused initial bacterial reduction up to 4 log10 CFU/ml with regrowth at about 32 h of exposure, which stayed at initial inoculum levels for the duration of the model for all three strains.

CONCLUSIONS

Dalbavancin inoculum effect is a major issue in bacterial infections with high bacterial loads and the combination of DAL plus single dose of DAP showed promise in eradicating resistant S. aureus strains at high inoculums.

Phage-Antibiotic Cocktail Rescues Daptomycin and Phage Susceptibility against Daptomycin-Nonsusceptible Enterococcus faecium in a Simulated Endocardial Vegetation Ex Vivo Model

Enterococcus faecium is a difficult-to-treat pathogen with emerging resistance to most clinically available antibiotics. Daptomycin (DAP) is the standard of care, but even high DAP doses (12 mg/kg body weight/day) failed to eradicate some vancomycin-resistant strains. Combination DAP-ceftaroline (CPT) may increase β-lactam affinity for target penicillin binding proteins (PBP); however, in a simulated endocardial vegetation (SEV) pharmacokinetic/pharmacodynamic (PK/PD) model, DAP-CPT did not achieve therapeutic efficacy against a DAP-nonsusceptible (DNS) vancomycin-resistant E. faecium (VRE) isolate. Phage-antibiotic combinations (PAC) have been proposed for resistant high-inoculum infections. We aimed to identify PAC with maximum bactericidal activity and prevention/reversal of phage and antibiotic resistance in an SEV PK/PD model against DNS isolate R497. Phage-antibiotic synergy (PAS) was evaluated with modified checkerboard MIC and 24-h time-kill analyses (TKA). Human-simulated antibiotic doses of DAP and CPT with phages NV-497 and NV-503-01 were then evaluated in 96-h SEV PK/PD models against R497. Synergistic and bactericidal activity was identified with the PAC of DAP-CPT combined with phage cocktail NV-497-NV-503-01, demonstrating a significant reduction in viability down to 3-log10 CFU/g (-Δ, 5.77-log10 CFU/g; P < 0.001). This combination also demonstrated isolate resensitization to DAP. Evaluation of phage resistance post-SEV demonstrated prevention of phage resistance for PACs containing DAP-CPT. Our results provide novel data highlighting bactericidal and synergistic activity of PAC against a DNS E. faecium isolate in a high-inoculum ex vivo SEV PK/PD model with subsequent DAP resensitization and prevention of phage resistance. IMPORTANCE Our study supports the additional benefit of standard-of-care antibiotics combined with a phage cocktail compared to antibiotic alone against a daptomycin-nonsusceptible (DNS) E. faecium isolate in a high-inoculum simulated endocardial vegetation ex vivo PK/PD model. E. faecium is a leading cause of hospital-acquired infections and is associated with significant morbidity and mortality. Daptomycin is considered the first-line therapy for vancomycin-resistant E. faecium (VRE), but the highest published doses have failed to eradicate some VRE isolates. The addition of a β-lactam to daptomycin may result in synergistic activity, but previous in vitro data demonstrate that daptomycin plus ceftaroline failed to eradicate a VRE isolate. Phage therapy as an adjunct to antibiotic therapy has been proposed as a salvage therapy for high-inoculum infections; however, pragmatic clinical comparison trials for endocarditis are lacking and difficult to design, reinforcing the timeliness of such analysis.

Therapeutics for Vancomycin-Resistant Enterococcal Bloodstream Infections

Vancomycin-resistant enterococci (VRE) are common causes of bloodstream infections (BSIs) with high morbidity and mortality rates. They are pathogens of global concern with a limited treatment pipeline. Significant challenges exist in the management of VRE BSI, including drug dosing, the emergence of resistance, and the optimal treatment for persistent bacteremia and infective endocarditis. Therapeutic drug monitoring (TDM) for antimicrobial therapy is evolving for VRE-active agents; however, there are significant gaps in the literature for predicting antimicrobial efficacy for VRE BSIs. To date, TDM has the greatest evidence for predicting drug toxicity for the three main VRE-active antimicrobial agents daptomycin, linezolid, and teicoplanin. This article presents an overview of the treatment options for VRE BSIs, the role of antimicrobial dose optimization through TDM in supporting clinical infection management, and challenges and perspectives for the future.

Meropenem MICs at Standard and High Inocula and Mutant Prevention Concentration Inter-Relations: Comparative Study with Non-Carbapenemase-Producing and OXA-48-, KPC- and NDM-Producing Klebsiella pneumoniae

The minimal inhibitory concentration (MIC) is conventionally used to define in vitro levels of susceptibility or resistance of a specific bacterial strain to an antibiotic and to predict its clinical efficacy. Along with MIC, other measures of bacteria resistance exist: the MIC determined at high bacterial inocula (MIC_HI) that allow the estimation of the occurrence of inoculum effect (IE) and the mutant prevention concentration, MPC. Together, MIC, MIC_HI and MPC represent the bacterial "resistance profile". In this paper, we provide a comprehensive analysis of such profiles of K. pneumoniae strains that differ by meropenem susceptibility, ability to produce carbapenemases and specific carbapenemase types. In addition, we have analyzed inter-relations between the MIC, MIC_HI and MPC for each tested K. pneumoniae strain. Low IE probability was detected with carbapenemase-non-producing K. pneumoniae, and high IE probability was detected with those that were carbapenemase-producing. MICs did not correlate with the MPCs; significant correlation was observed between the MIC_HIs and the MPCs, indicating that these bacteria/antibiotic characteristics display similar resistance properties of a given bacterial strain. To determine the possible resistance-related risk due to a given K. pneumoniae strain, we propose determining the MIC_HI. This can more or less predict the MPC value of the particular strain.

A High Daptomycin Dose Is Associated with Better Bacterial Clearance in Infections Caused by Vancomycin-Resistant Enterococcus faecium Regardless of Daptomycin Minimum Inhibitory Concentration in a Rat Infective Endocarditis Model

A high daptomycin dose has been suggested for treating vancomycin-resistant Enterococcus faecium (VREf) infections. However, even a 12 mg/kg daptomycin dose might be insufficient for treating VREf with high daptomycin minimum inhibitory concentrations (MICs). Additionally, animal pharmacodynamic and infection models to confirm the efficacy of 12 mg/kg daptomycin are lacking. Male Wistar rats were used for pharmacokinetic profiling and for the development of an infective endocarditis (IE) model. Daptomycin-susceptible dose-dependent VREf (DSE) (MIC of 0.5 mg/L) and daptomycin nonsusceptible VREf (DNSE) (MIC of 8 mg/L) were used for the IE models. The bacterial load of vegetation was the primary outcome and was evaluated after 3 days of daptomycin treatment. Daptomycin administered subcutaneously (s.c.) at 45 and 90 mg/kg, which corresponded to maximum serum concentrations (Cmax) of 122.6 mg/L and 178.5 mg/L, respectively, was equivalent to doses of 8 mg/kg and 12 mg/kg, respectively, in humans. The Cmax/MIC value was correlated with the bacterial load of vegetation after treatment (r = -0.88, P < 0.001). The 90 mg/kg s.c. group showed a significantly lower bacterial load of vegetation (log10 CFU/g) than the 45 mg/kg s.c. group against DSE (0 versus 4.75, P < 0.001) and DNSE (5.12 versus 6.98, P = 0.002). The 90 mg/kg s.c. group did not sterilize the vegetation against DNSE. Although the human equivalent dose of 12 mg/kg daptomycin was more effective than the smaller dose in reducing the bacterial load in DSE and DNSE IE, the dose could not sterilize the vegetation during a DNSE treatment. Further treatment strategies by which to manage severe VREf infections, especially at high daptomycin MICs, are urgently needed. IMPORTANCE Using a rat IE model with pharmacokinetic analysis, the treatment response of VREf IE was found to be daptomycin dose-dependent, presented as Cmax/MIC or as the 24 h area under the concentration-time curve (AUC0-24)/MIC. Daptomycin 90 mg/kg s.c. significantly reduced the bacterial load against DSE and DNSE. It also showed significant activity against DSE and DNSE, compared to 45 mg/kg s.c. Although daptomycin 90 mg/kg can eradicate the bacterial load after 3 days of treatment against DSE, eradication cannot be achieved with 90 mg/kg daptomycin against DNSE.

Daptomycin area under the curve to minimum inhibitory concentration ratio by broth microdilution for predicting the outcome of vancomycin-resistant Enterococcus bloodstream infection

OBJECTIVES

Different methods are used to determine the minimum inhibitory concentration (MIC) for daptomycin. The threshold is unknown for the free drug area under the concentration-time curve to MIC ratio (fAUC/MIC) of daptomycin using broth microdilution (BMD) to predict outcome of vancomycin-resistant enterococcus (VRE) bacteremia. The MIC testing method which is best for predicting the outcome remains unclear.

METHODS

This is a retrospective cohort study. The inclusion criterion was VRE bacteremia treated with ≥ 8 mg/kg of daptomycin. As we aimed to compare different daptomycin MIC testing methods for predicting the clinical outcome of VRE bacteremia, the inclusion criteria included the availability of MIC values for BMD, Etest, and automated antimicrobial susceptibility testing (AST). The primary end point was 28-day mortality. The fAUC/MIC was dichotomized using classification and regression tree analysis for predicting survival.

RESULTS

A total of 393 patients were included; 215 survived and 178 died. In the multivariable logistic model for predicting mortality, the dichotomized fAUC/MICs for Etest and AST were 0.508 and 0.065 times as probable, respectively, as that for BMD to minimize information loss. An fAUC/MIC > 75.07 for BMD significantly predicted lower mortality (adjusted odds ratio, 0.53, 95% confidence interval, 0.30-0.95; P = 0.03) after adjusting for underlying disease and bacteremia severity. Using Monte Carlo simulation, none of the doses had a probability of target attainment of ≥ 50% with an MIC of ≥ 2 mg/L.

CONCLUSION

The dichotomized threshold for fAUC/MIC for BMD was the best predictor of mortality. An fAUC/MIC > 75.07 for BMD independently predicted better survival.

Antimicrobial Susceptibility Testing for Enterococci

Enterococci are major, recalcitrant nosocomial pathogens with a wide repertoire of intrinsic and acquired resistance determinants and the potential of developing resistance to all clinically available antimicrobials. As such, multidrug-resistant enterococci are considered a serious public health threat. Due to limited treatment options and rapid emergence of resistance to all novel agents, the clinical microbiology laboratory plays a critical role in deploying accurate, reproducible, and feasible antimicrobial susceptibility testing methods to guide appropriate treatment of patients with deep-seated enterococcal infections. In this review, we provide an overview of the advantages and disadvantages of existing manual and automated methods that test susceptibility of Enterococcus faecium and Enterococcus faecalis to β-lactams, aminoglycosides, vancomycin, lipoglycopeptides, oxazolidinones, novel tetracycline-derivatives, and daptomycin. We also identify unique problems and gaps with the performance and clinical utility of antimicrobial susceptibility testing for enterococci, provide recommendations for clinical laboratories to circumvent select problems, and address potential future innovations that can bridge major gaps in susceptibility testing.

Phage Cocktails with Daptomycin and Ampicillin Eradicates Biofilm-Embedded Multidrug-Resistant Enterococcus faecium with Preserved Phage Susceptibility

Multidrug-resistant (MDR) Enterococcus faecium is a challenging nosocomial pathogen known to colonize medical device surfaces and form biofilms. Bacterio (phages) may constitute an emerging anti-infective option for refractory, biofilm-mediated infections. This study evaluates eight MDR E. faecium strains for biofilm production and phage susceptibility against nine phages. Two E. faecium strains isolated from patients with bacteremia and identified to be biofilm producers, R497 (daptomycin (DAP)-resistant) and HOU503 (DAP-susceptible dose-dependent (SDD), in addition to four phages with the broadest host ranges (ATCC 113, NV-497, NV-503-01, NV-503-02) were selected for further experiments. Preliminary phage-antibiotic screening was performed with modified checkerboard minimum biofilm inhibitory concentration (MBIC) assays to efficiently screen for bacterial killing and phage-antibiotic synergy (PAS). Data were compared by one-way ANOVA and Tukey (HSD) tests. Time kill analyses (TKA) were performed against R497 and HOU503 with DAP at 0.5× MBIC, ampicillin (AMP) at free peak = 72 µg/mL, and phage at a multiplicity of infection (MOI) of 0.01. In 24 h TKA against R497, phage-antibiotic combinations (PAC) with DAP, AMP, or DAP + AMP combined with 3- or 4-phage cocktails demonstrated significant killing compared to the most effective double combination (ANOVA range of mean differences 2.998 to 3.102 log10 colony forming units (CFU)/mL; p = 0.011, 2.548 to 2.868 log10 colony forming units (CFU)/mL; p = 0.023, and 2.006 to 2.329 log10 colony forming units (CFU)/mL; p = 0.039, respectively), with preserved phage susceptibility identified in regimens with 3-phage cocktails containing NV-497 and the 4-phage cocktail. Against HOU503, AMP combined with any 3- or 4-phage cocktail and DAP + AMP combined with the 3-phage cocktail ATCC 113 + NV-497 + NV-503-01 demonstrated significant PAS and bactericidal activity (ANOVA range of mean differences 2.251 to 2.466 log10 colony forming units (CFU)/mL; p = 0.044 and 2.119 to 2.350 log10 colony forming units (CFU)/mL; p = 0.028, respectively), however, only PAC with DAP + AMP maintained phage susceptibility at the end of 24 h TKA. R497 and HOU503 exposure to DAP, AMP, or DAP + AMP in the presence of single phage or phage cocktail resulted in antibiotic resistance stabilization (i.e., no antibiotic MBIC elevation compared to baseline) without identified antibiotic MBIC reversion (i.e., lowering of antibiotic MBIC compared to baseline in DAP-resistant and DAP-SDD isolates) at the end of 24 h TKA. In conclusion, against DAP-resistant R497 and DAP-SDD HOU503 E. faecium clinical blood isolates, the use of DAP + AMP combined with 3- and 4-phage cocktails effectively eradicated biofilm-embedded MDR E. faecium without altering antibiotic MBIC or phage susceptibility compared to baseline.

Insertion sequences and other mobile elements associated with antibiotic resistance genes in Enterococcus isolates from an inpatient with prolonged bacteraemia

Insertion sequences (ISs) and other transposable elements are associated with the mobilization of antibiotic resistance determinants and the modulation of pathogenic characteristics. In this work, we aimed to investigate the association between ISs and antibiotic resistance genes, and their role in the dissemination and modification of the antibiotic-resistant phenotype. To that end, we leveraged fully resolved Enterococcus faecium and Enterococcus faecalis genomes of isolates collected over 5 days from an inpatient with prolonged bacteraemia. Isolates from both species harboured similar IS family content but showed significant species-dependent differences in copy number and arrangements of ISs throughout their replicons. Here, we describe two inter-specific IS-mediated recombination events and IS-mediated excision events in plasmids of E. faecium isolates. We also characterize a novel arrangement of the ISs in a Tn1546-like transposon in E. faecalis isolates likely implicated in a vancomycin genotype–phenotype discrepancy. Furthermore, an extended analysis revealed a novel association between daptomycin resistance mutations in liaSR genes and a putative composite transposon in E. faecium, offering a new paradigm for the study of daptomycin resistance and novel insights into its dissemination. In conclusion, our study highlights the role ISs and other transposable elements play in the rapid adaptation and response to clinically relevant stresses such as aggressive antibiotic treatment in enterococci.

Eradication of Biofilm-Mediated Methicillin-Resistant Staphylococcus aureus Infections In Vitro: Bacteriophage-Antibiotic Combination

Bacterial biofilms are difficult to eradicate and can complicate many infections by forming on tissues and medical devices. Phage+antibiotic combinations (PAC) may be more active on biofilms than either type of agent alone, but it is difficult to predict which PAC regimens will be reliably effective. To establish a method for screening PAC combinations against Staphylococcus aureus biofilms, we conducted biofilm time-kill analyses (TKA) using various combinations of phage Sb-1 with clinically relevant antibiotics. We determined the activity of PAC against biofilm versus planktonic bacteria and investigated the emergence of resistance during (24 h) exposure to PAC. As expected, fewer treatment regimens were effective against biofilm than planktonic bacteria. In experiments with isogenic strain pairs, we also saw less activity of PACs against DNS-VISA mutants versus their respective parentals. The most effective treatment against both biofilm and planktonic bacteria was the phage+daptomycin+ceftaroline regimen, which met our stringent definition of bactericidal activity (>3 log10 CFU/mL reduction). With the VISA-DNS strain 8015 and DNS strain 684, we detected anti-biofilm synergy between Sb-1 and DAP in the phage+daptomycin regimen (>2 log10 CFU/mL reduction versus best single agent). We did not observe any bacterial resensitization to antibiotics following treatment, but phage resistance was avoided after exposure to PAC regimens for all tested strains. The release of bacterial membrane vesicles tended to be either unaffected or reduced by the various treatment regimens. Interestingly, phage yields from certain biofilm experiments were greater than from similar planktonic experiments, suggesting that Sb-1 might be more efficiently propagated on biofilm. IMPORTANCE Biofilm-associated multidrug-resistant infections pose significant challenges for antibiotic therapy. The extracellular polymeric matrix of biofilms presents an impediment for antibiotic diffusion, facilitating the emergence of multidrug-resistant populations. Some bacteriophages (phages) can move across the biofilm matrix, degrade it, and support antibiotic penetration. However, little is known about how phages and their hosts interact in the biofilm environment or how different phage+antibiotic combinations (PACs) impact biofilms in comparison to the planktonic state of bacteria, though scattered data suggest that phage+antibiotic synergy occurs more readily under biofilm-like conditions. Our results demonstrated that phage Sb-1 can infect MRSA strains both in biofilm and planktonic states and suggested PAC regimens worthy of further investigation as adjuncts to antibiotics.

Evaluation of Bacteriophage-Antibiotic Combination Therapy for Biofilm-Embedded MDR Enterococcus faecium

Multidrug-resistant (MDR) Enterococcus faecium is a challenging pathogen known to cause biofilm-mediated infections with limited effective therapeutic options. Lytic bacteriophages target, infect, and lyse specific bacterial cells and have anti-biofilm activity, making them a possible treatment option. Here, we examine two biofilm-producing clinical E. faecium strains, daptomycin (DAP)-resistant R497 and DAP-susceptible dose-dependent (SDD) HOU503, with initial susceptibility to E. faecium bacteriophage 113 (ATCC 19950-B1). An initial synergy screening was performed with modified checkerboard MIC assays developed by our laboratory to efficiently screen for antibiotic and phage synergy, including at very low phage multiplicity of infection (MOI). The data were compared by one-way ANOVA and Tukey (HSD) tests. In 24 h time kill analyses (TKA), combinations with phage-DAP-ampicillin (AMP), phage-DAP-ceftaroline (CPT), and phage-DAP-ertapenem (ERT) were synergistic and bactericidal compared to any single agent (ANOVA range of mean differences 3.34 to 3.84 log10 CFU/mL; p < 0.001). Furthermore, phage-DAP-AMP and phage-DAP-CPT prevented the emergence of DAP and phage resistance. With HOU503, the combination of phage-DAP-AMP showed the best killing effect, followed closely by phage-DAP-CPT; both showed bactericidal and synergistic effects compared to any single agent (ANOVA range of mean differences 3.99 to 4.08 log10 CFU/mL; p < 0.001).

Novel human in vitro vegetation simulation model for infective endocarditis

Infective endocarditis (IE) is a heart valve infection with high mortality rates. IE results from epithelial lesions, inducing sterile healing vegetations consisting of platelets, leucocytes, and fibrin that are susceptible for colonization by temporary bacteremia. Clinical testing of new treatments for IE is difficult and fast models sparse. The present study aimed at establishing an in vitro vegetation simulation IE model for fast screening of novel treatment strategies. A healing promoting platelet and leucocyte-rich fibrin patch was used to establish an IE organoid-like model by colonization with IE-associated bacterial isolates Staphylococcus aureus, Streptococcus spp (S. mitis group), and Enterococcus faecalis. The patch was subsequently exposed to tobramycin, ciprofloxacin, or penicillin. Bacterial colonization was evaluated by microscopy and quantitative bacteriology. We achieved stable bacterial colonization on the patch, comparable to clinical IE vegetations. Microscopy revealed uneven, biofilm-like colonization of the patch. The surface-associated bacteria displayed increased tolerance to antibiotics compared to planktonic bacteria. The present study succeeded in establishing an IE simulation model with the relevant pathogens S. aureus, S. mitis group, and E. faecalis. The findings indicate that the IE model mirrors the natural IE process and has the potential for fast screening of treatment candidates.

Evaluation of Bacteriophage Cocktails Alone and in Combination with Daptomycin Against Daptomycin-Nonsusceptible Enterococcus faecium

Enterococcus faecium(E. fcm) is a significant multidrug-resistant pathogen. Bacteriophage cocktails are being proposed to complement antibiotic therapy. After a screen of 8 E. fcm strains against 4 phages, two phages(113, 9184) with the broadest host ranges were chosen for further experiments. Transmission electron microscopy, whole-genome sequencing, comparative genome analyses, and time-kill analyses were performed. Daptomycin(DAP) plus phage cocktail(113:myophage;9184:siphopage) showed bactericidal activity in most regimens, while DAP addition prevented phage 9184 resistance against daptomycin non-susceptible E. fcm.

Anti-biofilm Approach in Infective Endocarditis Exposes New Treatment Strategies for Improved Outcome

Infective endocarditis (IE) is a life-threatening infective disease with increasing incidence worldwide. From early on, in the antibiotic era, it was recognized that high-dose and long-term antibiotic therapy was correlated to improved outcome. In addition, for several of the common microbial IE etiologies, the use of combination antibiotic therapy further improves outcome. IE vegetations on affected heart valves from patients and experimental animal models resemble biofilm infections. Besides the recalcitrant nature of IE, the microorganisms often present in an aggregated form, and gradients of bacterial activity in the vegetations can be observed. Even after appropriate antibiotic therapy, such microbial formations can often be identified in surgically removed, infected heart valves. Therefore, persistent or recurrent cases of IE, after apparent initial infection control, can be related to biofilm formation in the heart valve vegetations. On this background, the present review will describe potentially novel non-antibiotic, antimicrobial approaches in IE, with special focus on anti-thrombotic strategies and hyperbaric oxygen therapy targeting the biofilm formation of the infected heart valves caused by Staphylococcus aureus. The format is translational from preclinical models to actual clinical treatment strategies.

Daptomycin versus Glycopeptides for the Treatment of Enterococcus faecium Bacteraemia: A Cohort Study

Background: Ampicillin resistant and glycopeptide susceptible Enterococcus faecium bloodstream infection (GSEF-BSI) incidence has risen. However, the treatment of choice remains unknown. Daptomycin use for the treatment of enterococcal infections has increased, despite effectiveness and safety concerns. The objective was to compare the effectiveness and safety of daptomycin and glycopeptides in the treatment of GSEF-BSI. Methods: This was a single-centre, retrospective observational cohort study performed at Hospital del Mar (Barcelona, Spain), from January 2006–May 2018. The primary outcome was clinical cure at the end of the therapy, and secondary outcomes included 14-day, 30-day, in-hospital mortality, and length of stay. Results: From a total of 192 patients with GSEF-BSI, 54 (28.1%) were treated with glycopeptides and 17 (8.9%) with daptomycin. Patients treated with daptomycin presented a lower clinical cure than patients treated with glycopeptides (58.8% vs. 83.3%, RR 0.416 (95% CI 0.189–0.915)). After controlling for confounding variables by means of multivariate analysis the significative difference was confirmed (aOR 4.313, 95% CI, 1.053–17.660). The need for treatment discontinuation due to adverse events was similar. Conclusions: Patients with GSEF-BSI treated with glycopeptides showed a higher clinical cure than those treated with daptomycin.

High-Dose Daptomycin and Clinical Applications

OBJECTIVE

To evaluate evidence for high-dose daptomycin (doses ≥ 8 mg/kg/d).

DATA SOURCES

A PubMed/MEDLINE literature search was performed (January 2000 to December 2020) using the search terms daptomycin, high dose, and dosing. Review article references and society guidelines were reviewed.

STUDY SELECTION AND DATA EXTRACTION

Clinical trials, observational studies, retrospective studies, meta-analyses, and systematic reviews reporting on high-dose daptomycin were included.

DATA SYNTHESIS

Experimentally, daptomycin outperforms other antimicrobials for high inoculum and biofilm-associated infections. Clinically, high-dose daptomycin is supported as salvage and first-line therapy for endocarditis and bacteremia, primarily when caused by methicillin-resistant Staphylococcus aureus (when vancomycin minimum inhibitory concentration is >1 mg/L) and Enterococcus. High-dose daptomycin appears effective for osteomyelitis and central nervous system infections, although comparative studies are lacking. High dosing in renal replacement therapy requires considering clearance modality to achieve exposures like normal renal function. Weight-based dosing in obesity draws concern for elevated exposures, although high doses have not been evaluated kinetically in obesity. Some data show benefits of high doses in overweight populations. Burn patients clear daptomycin more rapidly, and high doses may only achieve drug exposures similar to standard doses (6 mg/kg).

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

This review analyzes the efficacy and safety of high-dose daptomycin in serious gram-positive infections. Discussion of specific infectious etiologies and patient populations should encourage clinicians to evaluate their daptomycin dosing standards.

CONCLUSIONS

The efficacy of high-dose daptomycin and limited safety concerns encourage clinicians to consider high-dose daptomycin more liberally in severe gram-positive infections.

Bacteriophage AB-SA01 Cocktail in Combination with Antibiotics against MRSA-VISA Strain in an In Vitro Pharmacokinetic/Pharmacodynamic Model

This study aimed to test the efficacy of bacteriophage-antibiotic combinations (BACs) in vitro in 24-h time-kill settings and in ex vivo simulated endocardial vegetation (SEV) pharmacokinetic/pharmacodynamic models for 96 h. BACs prevented the development of bacteriophage resistance, while some bacteriophage resistance emerged in bacteriophage-alone treatments. In addition, BACs resulted in an enhancement of bacterial eradication in SEV models. Our findings support the potential activity of BAC therapy for combating serious methicillin-resistant Staphylococcus aureus (MRSA) infections.

Mechanistic Insights Into the Differential Efficacy of Daptomycin Plus β-Lactam Combinations Against Daptomycin-Resistant Enterococcus faecium

BACKGROUND

The combination of daptomycin (DAP) plus ampicillin (AMP), ertapenem (ERT), or ceftaroline has been demonstrated to be efficacious against a DAP-tolerant Enterococcus faecium strain (HOU503). However, the mechanism for the efficacy of these combinations against DAP-resistant (DAP-R) E. faecium strains is unknown.

METHODS

We investigated the efficacy of DAP in combination with AMP, ERT, ceftaroline, ceftriaxone, or amoxicillin against DAP-R E. faecium R497 using established in vitro and in vivo models. We evaluated pbp expression, levels of penicillin-binding protein (PBP) 5 (PBP5) and β-lactam binding affinity in HOU503 versus R497.

RESULTS

DAP plus AMP was the only efficacious regimen against DAP-R R497 and prevented emergence of resistance. DAP at 8, 6, and 4 mg/kg in combination with AMP was efficacious but showed delayed killing compared with 10 mg/kg. PBP5 of HOU503 exhibited amino acid substitutions in the penicillin-binding domain relative to R497. No difference in pbp mRNA or PBP5 levels was detected between HOU503 and R497. labeling of PBPs with Bocillin FL, a fluorescent penicillin derivative, showed increased β-lactam binding affinity of PBP5 of HOU503 compared with that of R497.

CONCLUSIONS

Only DAP (10 mg/kg) plus AMP or amoxicillin was efficacious against a DAP-R E. faecium strain, and pbp5 alleles may be important contributors to efficacy of DAP plus β-lactam therapy.

Bacteriophage-Antibiotic Combinations for Enterococcus faecium with Varying Bacteriophage and Daptomycin Susceptibilities

Concerns regarding increased prevalence of daptomycin (DAP)-resistant strains necessitate novel therapies for Enterococcus faecium infections. Obligately lytic bacteriophages are viruses that target, infect, and kill bacterial cells. Limited studies have evaluated phage-antibiotic combinations against E. faecium After an initial screen of eight E. faecium strains, three strains with varying DAP/phage susceptibilities were selected for further experiments. Phage-to-strain specificity contributed to synergy with antibiotics by time-kill analyses and was associated with lower development of phage resistance.

Bacteriophage-Antibiotic Combination Strategy: an Alternative against Methicillin-Resistant Phenotypes of Staphylococcus aureus

Comparative time-kill experiments with Staphylococcus aureus bacteriophage (phage) Sb-1 alone and phage-antibiotic combinations (PACs) against two methicillin-resistant S. aureus (MRSA) strains have shown synergy with both daptomycin-phage and vancomycin-phage combinations. PACs prevented development of phage resistance and demonstrated bactericidal activity for all triple combinations. In addition, the extracellular membrane vesicle (MV) formation and the potential impact of phage on MV suppression were examined. Our results demonstrate the potential of PAC for combating MRSA infections.

Tedizolid as Step-Down Therapy following Daptomycin versus Continuation of Daptomycin against Enterococci and Methicillin- and Vancomycin-Resistant Staphylococcus aureus in a Rat Endocarditis Model

Tedizolid (TZD) and daptomycin (DAP) were assessed in a rat endocarditis model against Enterococcus faecalis, Enterococcus faecium (resistant to vancomycin and ampicillin), and Staphylococcus aureus As a monotherapy, TZD for 5 days was not effective in a comparison with no-treatment controls, while DAP for 5 days was significantly effective against these bacteria. Step-down therapy (DAP for 3 days followed by TZD for 2 days) was as effective as DAP for 5 days and was comparable to 3 days of DAP plus ceftriaxone against all bacteria and to 3 days of DAP plus gentamicin against E. faecalis OG1RF.

Impact of Daptomycin Dose Exposure Alone or in Combination with β-Lactams or Rifampin against Vancomycin-Resistant Enterococci in an In Vitro Biofilm Model

Enterococcus faecium strains are commonly resistant to vancomycin and β-lactams. In addition, E. faecium often causes biofilm-associated infections and these infections are difficult to treat. In this context, we investigated the activity of dosing regimens using daptomycin (DAP) (8, 10, 12, and 14 mg/kg of body weight/day) alone and in combination with ceftaroline (CPT), ampicillin (AMP), ertapenem (ERT), and rifampin (RIF) against 2 clinical strains of biofilm-producing vancomycin-resistant Enterococcus faecium (VREfm), namely, strains S447 and HOU503, in an in vitro biofilm model. HOU503 harbors common LiaS and LiaR substitutions, whereas S447 lacks mutations associated with the LiaFSR pathway. MIC results demonstrated that both strains were susceptible to DAP and resistant to CPT, AMP, ERT, and RIF. The 168-h pharmacokinetic/pharmacodynamic (PK/PD) CDC biofilm reactor models (simulating human antibiotic exposures) were used with titanium and polyurethane coupons to evaluate the efficacy of antibiotic combinations. DAP 12 and 14 achieved bactericidal activity against S447 but lacked such effect against HOU503. Addition of ERT and RIF enhanced DAP activity, allowing DAP 8 and 10 plus ERT or RIF to produce bactericidal activity against both strains at 168 h. While DAP 8 and 10 plus CPT improved killing, they did not reach bactericidal reduction against S447. Combination of AMP, CPT, ERT, or RIF resulted in enhanced and bactericidal activity for DAP against HOU503 at 168 h. Our data provide further support for the use of combinations of DAP with AMP, ERT, CPT, and RIF in infections caused by biofilm producing VREfm. Further research involving DAP combinations against biofilm-producing enterococci is warranted.

Optimizing the Dosing Regimens of Daptomycin Based on the Susceptible Dose-Dependent Breakpoint against Vancomycin-Resistant Enterococci Infection

Daptomycin, a lipopeptide antibiotic, is one of the therapeutic options used for the treatment of vancomycin-resistant enterococci (VRE). Recently, the Clinical and Laboratory Standards Institute (CLSI) M100 30th edition has removed the susceptibility (S) breakpoint for Enterococcus faecium and replaced it with a susceptible dose-dependent (SDD) breakpoint of ≤4 μg/mL, with a suggested dosage of 8–12 mg/kg/day. Herein, we aimed to determine the minimum inhibitory concentration (MIC) values of daptomycin against clinical VRE isolates and to study the appropriate daptomycin dosing regimens among critically ill patients based on the new susceptibility CLSI breakpoint. The MIC determination of daptomycin was performed using E-test strips among clinical VRE strains isolated from patients at the Phramongkutklao Hospital. We used Monte Carlo simulation to calculate the probability of target attainment (PTA) and the cumulative fraction of response (CFR) of the ratio of the free area under the curve to MIC (fAUC_0–24/MIC) > 27.4 and fAUC_0–24/MIC > 20 for survival and microbiological response, respectively, at the first day and steady state. Further, we determined that the simulated daptomycin dosing regimen met the minimum concentration (Cmin) requirements for safety of being below 24.3 mg/L. All of the 48 VRE isolates were E. faecium strains, and the percentiles at the 50th and 90th MIC of daptomycin were 1 and 1.5 μg/mL, respectively. At MIC ≤ 2 μg/mL, a daptomycin dosage of 12 mg/kg/day achieved the PTA target of survival and microbiological response at the first 24 h time point and steady state. For a MIC of 4 μg/mL, none of the dosage regimens achieved the PTA target. For CFR, a dosage of 8–12 mg/kg/day could achieve the 90% CFR target at the first day and steady state. All dosing regimens had a low probability of Cmin being greater than 24.3 mg/L. In conclusion, the MIC of VRE against daptomycin is quite low, and loading and maintenance doses with 8 mg/kg/day were determined to be optimal and safe.

Pharmacodynamics of daptomycin in combination with other antibiotics for the treatment of enterococcal bacteraemia

Daptomycin is commonly prescribed in combination with other antibiotics for treatment of enterococcal bacteraemia. Whilst a free drug area under the concentration-time curve to minimum inhibitory concentration (fAUC/MIC) ratio >27.4 is associated with 30-day survival with daptomycin monotherapy, it is unknown whether receipt of other antibiotics affects this threshold. Data were pooled from seven published trials assessing outcomes in daptomycin-treated enterococcal bacteraemia, including patients receiving daptomycin (≥72 h) and any β-lactam, intravenous aminoglycoside, linezolid, tigecycline and/or vancomycin. Exposures were calculated using a published population pharmacokinetic model based on creatinine clearance, 90% protein binding and daptomycin Etest MIC. The fAUC/MIC threshold predictive of 30-day survival was determined by classification and regression tree analysis. Following pooling of data, 240 adults were included; 137 (57.1%) were alive at 30 days. A majority of patients were immunosuppressed (65.8%) and received a β-lactam (94.6%). Examining the threshold in low-acuity patients (n = 135) to control for co-morbidities, these patients were more likely to survive when fAUC/MIC >12.3 was achieved (63.2% vs. 20.0%; P = 0.015). The difference remained significant in a multivariable logistic regression model that controlled for infection source and immunosuppression (P = 0.017). This threshold is 2-fold lower than that observed with daptomycin monotherapy. Probabilities of threshold attainment using a 10 mg/kg/day dose were 100% for isolates with MICs ≤ 2 mg/L and 95.2% for a 12 mg/kg/day dose for MICs of 4 mg/L. These data support the use of high-dose daptomycin in combination with another antibiotic for treatment of enterococcal bacteraemia.

The New, New Daptomycin Breakpoint for Enterococcus spp

In 2019, the Clinical and Laboratory Standards Institute revised the daptomycin breakpoints for Enterococcus spp. twice in rapid succession. Analyses leading to these revisions included review of testing issues, murine and human in vivo pharmacodynamics, safety of off-label doses, and treatment outcomes. The data review brought up a dilemma that is encountered with increasing frequency: a breakpoint supported by pharmacokinetic/pharmacodynamic modeling that bisected the wild-type Enterococcus faecium MIC distribution. In such instances, not only does the probability of pharmacokinetic/pharmacodynamic targets need to be taken into account but also the probability that the laboratory can generate an accurate MIC that is reproducible within one interpretive category.

Daptomycin Dose-Ranging Evaluation with Single-Dose versus Multidose Ceftriaxone Combinations against Streptococcus mitis/oralis in an Ex Vivo Simulated Endocarditis Vegetation Model

The viridans group streptococci (VGS) are a heterogeneous group of organisms which are important components of the normal human oral flora. Among the VGS, the Streptococcus mitis /oralis subgroup is one of the most common causes of infective endocarditis (IE). Daptomycin (DAP) is a potential alternative therapeutic option for invasive S. mitis infections, given high rates of β-lactam resistance and vancomycin tolerance in such strains. However, the ability of these strains to rapidly evolve high-level and durable DAP resistance (DAP-R) is problematic. Recent data suggest that combination DAP-β-lactam therapy circumvents this issue. Human-simulated dose-escalating DAP-alone dose regimens (6, 8, 10, or 12 mg/kg/day times 4 days) versus DAP (6 mg/kg/day) plus ceftriaxone (CRO) (2 g once daily times 4 days or 0.5 g, single dose) were assessed against two prototypical DAP-susceptible (DAP-S) S. mitis /oralis strains (SF100 and 351), as measured by a pharmacokinetic/pharmacodynamic (PK/PD) model of simulated endocardial vegetations (SEVs). No DAP-alone regimen was effective, with regrowth of high-level DAP-R isolates observed for both strains over 96-h exposures. Combinations of DAP-CRO with either single- or multidose regimens yielded significant reductions in log₁₀ CFU/g amounts within SEVs for both strains (∼6 log₁₀ CFU/g) within 24 h. In addition, no DAP-R strains were detected in either DAP-CRO combination regimens over the 96-h exposure. In contrast to prior in vitro studies, no perturbations in two key cardiolipin biosynthetic genes (cdsA and pgsA) were identified in DAP-R SEV isolates emerging from strain 351, despite defective phospholipid production. The combination of DAP-CRO warrants further investigation for treatment of IE due to S. mitis /oralis.

Novel Strategies for the Management of Vancomycin-Resistant Enterococcal Infections

PURPOSE OF REVIEW

Vancomycin-resistant enterococci (VRE) are important nosocomial pathogens that commonly affect critically ill patients. VRE have a remarkable genetic plasticity allowing them to acquire genes associated with antimicrobial resistance. Therefore, the treatment of deep-seated infections due to VRE has become a challenge for the clinician. The purpose of this review is to assess the current and future strategies for the management of recalcitrant deep-seated VRE infections and efforts for infection control in the hospital setting.

RECENT FINDINGS

Preventing colonization and decolonization of multidrug-resistant bacteria are becoming the most promising novel strategies to control and eradicate VRE from the hospital environment. Fecal microbiota transplantation (FMT) has shown remarkable results on treating colonization and infection due to Clostridiodes difficille and VRE, as well as to recover the integrity of the gut microbiota under antibiotic pressure. Initial reports have shown the efficacy of FMT on reestablishing patient microbiota diversity in the gut and reducing the dominance of VRE in the gastrointestinal tract. In addition, the use of bacteriophages may be a promising strategy in eradicating VRE from the gut of patients. Until these strategies become widely available in the hospital setting, the implementation of infection control measures and stewardship programs are paramount for the control of this pathogen and each program should provide recommendations for the proper use of antibiotics and develop strategies that help to detect populations at risk of VRE colonization, prevent and control nosocomial transmission of VRE, and develop educational programs for all healthcare workers addressing the epidemiology of VRE and the potential impact of these pathogens on the cost and outcomes of patients. In terms of antibiotic strategies, daptomycin has become the standard of care for the management of deep-seated infections due to VRE. However, recent evidence indicates that the efficacy of this antibiotic is limited, and higher (10-12 mg/kg) doses and/or combination with β-lactams is needed for therapeutic success. Clinical data to support the best use of daptomycin against VRE are urgently needed. This review provides an overview of recent developments regarding the prevention, treatment, control, and eradication of VRE in the hospital setting. We aim to provide an update of the most recent therapeutic strategies to treat deep-seated infections due to VRE.