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Background There is in vitro and clinical evidence to suggest daptomycin has good activity against Enterococcus. In 2019, CLSI produced clinical breakpoints for Enterococcus spp. Objectives To describe the distribution of MICs of daptomycin for enterococcal bloodstream infection (EBSI) isolates in a large Scottish health board, the indications for local daptomycin susceptibility testing and daptomycin doses used in vancomycin-resistant Enterococcus faecium (VREfm) infection. Methods We investigated all EBSIs over a 21 month period and identified isolates tested against daptomycin. We recorded the distribution of MICs, as well as indications for daptomycin susceptibility testing and information on daptomycin dosing, where it was used. Results There were 293 blood culture isolates of Enterococcus spp., of which 37 had daptomycin susceptibility testing performed, from 31 individual patients. Of the 293 isolates, 103 were E. faecium, of which 63 were VREfm. Daptomycin testing was indicated by vancomycin resistance in 24/37 isolates. All E. faecium isolates tested were in the CLSI ‘susceptible dose-dependent (SDD)’ range of MICs. All other Enterococcus spp. tested were in the ‘susceptible’ range. Twelve patients received daptomycin, and dosing information was recovered for 10. Nine of these patients received 8–12 mg/kg/day dosing. There were no recorded adverse drug reactions. Ten of 12 patients were alive at the time of data collection. Conclusions Daptomycin MIC distribution for EBSI isolates suggests a high local rate of susceptibility, according to CLSI breakpoints, in a population with high rates of VREfm. CLSI-recommended doses of daptomycin were used, with encouraging survival outcomes.

Objectives Synergistic combinations of daptomycin and β-lactam antibiotics are currently recommended for treatment of VRE bloodstream infection (BSI). The efficacy of these combinations is jeopardized by VRE inherently resistant to β-lactam antibiotics. The combination of daptomycin and fosfomycin is recommended as an alternative therapy for VRE BSI; however, clinical data to support use of this combination are lacking. Patients and methods We conducted a prospective observational multicentre study of patients treated with a combination of daptomycin and fosfomycin for VRE BSI during 2016–20. The primary outcome was 28 day mortality. Multivariable logistic regression was performed for outcome analysis. Results The study included 106 patients from 1112 VRE BSI episodes. The overall 28 day mortality was 40.6%. The median (IQR) daptomycin dose was 10.18 mg/kg (9.43–10.70). The fosfomycin dose was 16 g/day (8–22.5). Ninety-six isolates were available for MIC testing. The fosfomycin MIC was 32 mg/L in 6 (6.3%), 64 mg/L in 68 (70.8%) and ≥128 mg/L in 22 (22.9%) isolates. Independent of Charlson comorbidity index and Pitt bacteraemia score, fosfomycin MIC ≥128 mg/L [adjusted OR (aOR) = 3.05; 95% CI = 1.01–9.19; P = 0.047] and daptomycin dose (aOR = 0.64; 95% CI = 0.43–0.97; P = 0.04) predicted mortality. Conclusions Higher daptomycin dose and susceptibility to fosfomycin were independently associated with lower mortality in patients with VRE BSI. Our results suggest that higher doses of daptomycin are indicated for VRE BSI, whether or not it is used in combination with fosfomycin. The combination was less effective for patients with fosfomycin-resistant isolates.

Background The cyclic anionic lipopeptide daptomycin is used in the treatment of severe infections caused by Gram-positive pathogens, including MRSA. Daptomycin resistance, although rare, often results in treatment failure. Paradoxically, in MRSA, daptomycin resistance is usually accompanied by a concomitant decrease in β-lactam resistance in what is known as the ‘see-saw effect’. This resensitization is extensively used for the treatment of MRSA infections, by combining daptomycin and a β-lactam antibiotic, such as oxacillin. Objectives We aimed: (i) to investigate the combined effects of daptomycin and oxacillin on the lipid composition of the cellular membrane of both daptomycin-resistant and -susceptible MRSA strains; and (ii) to assess the involvement of the post-translocational protein PrsA, which plays an important role in oxacillin resistance in MRSA, in membrane lipid composition and remodelling during daptomycin resistance/β-lactam sensitization. Results The combination of microbiological and biochemical studies, with fluorescence microscopy using lipid probes, showed that the lipid composition and surface charge of the daptomycin-resistant cells exposed to daptomycin/oxacillin were dependent on antibiotic concentration and directly associated with PrsA, which influenced cardiolipin remodelling/relocation. Conclusions Our findings show that PrsA, in addition to its post-transcriptional role in the maturation of PBP 2a, is a key mediator of cell membrane remodelling connected to the see-saw effect and may have a key role in the resensitization of daptomycin-resistant strains to β-lactams, such as oxacillin.

Background Daptomycin is increasingly used in the treatment of bone and joint infections (BJIs) and may be responsible for daptomycin-induced eosinophilic pneumonia (DIEP), a potentially severe adverse drug reaction. The aim of this study was to describe DIEP in patients treated at a referral center for the management of BJI, and to revisit current definitions of this disease. Methods Patients treated from 1 January 2012 to 31 March 2021 were included in a prospective cohort (NCT02817711), in which all potential serious adverse events are prospectively recorded. Patients diagnosed with DIEP were retrospectively analyzed using different definitions. Results In a total of 4664 patients included in the cohort during the study period, 1021 patients (21.9%) received daptomycin, of whom 17 (1.7%) were diagnosed with DIEP. Most patients were male (n = 11 [64.7%]), and periprosthetic joint infection was the commonest BJI (n = 12 [70.6%]). Only 1 patient had bronchoalveolar lavage (BAL) eosinophil count ≥25%, while most patients had peripheral blood eosinophilia (n = 15 [88.2%]). Chest computed tomography (CT) was compatible with eosinophilic pneumonia in 13 of 14 cases (92.9%). All patients recovered upon discontinuation of daptomycin. Using the different definitions available, only a minority of cases fulfilled existing criteria for DIEP. We propose a new algorithm that includes specific CT scan signs, and systemic instead of BAL eosinophilia. Conclusions DIEP is a rare event that requires prompt discontinuation of the causative antibiotic. Current criteria to diagnose definite DIEP are too restrictive and not easily applicable in clinical practice. A new algorithm is proposed here (Lyon algorithm) to facilitate the early identification of DIEP.

Several studies have documented the synergy between vancomycin/daptomycin and various beta-lactams, and clinical studies have studied this combination therapy in humans. We review the published literature on this topic to know the utility of the combined treatment with beta-lactams in treating bacteraemia methicillin-resistant Staphylococcus aureus (MRSA) infections. Fifteen observational studies, three randomised clinical trials and three systematics reviews are analysed in this article. Observational studies used ceftaroline, cefazolin, piperacillin/tazobactam or cefepime among the beta-lactams. Clinical trials used cloxacillin or flucloxacillin as the most used beta-lactam in two trials and ceftaroline in one. Three systematic reviews are published. One of them only includes studies with vancomycin and included six studies. The other two systematic reviews include patients with daptomycin or vancomycin and included 15 and 9 studies, respectively. Adding a beta-lactam to vancomycin or daptomycin may help shorten bacteraemia and avoid recurrences in patients with MRSA bacteraemia. There is no evidence that combined therapy improves mortality. Nephrotoxicity in clinical trials precludes the use of combination therapy mainly with cloxacillin or flucloxacillin, but systematic reviews have not found a significant difference in this point in observational studies with other beta-lactams. The role of other beta-lactams such as ceftaroline should be thoroughly studied in these patients.

[Objectives] To evaluate the proficiency of microbiology laboratories in Spain in antimicrobial susceptibility testing (AST) of Staphylococcus spp., [Materials and methods] Eight Staphylococcus spp. with different resistance mechanisms were selected: six Staphylococcus aureus (CC-01/mecA, CC-02/mecC, CC-03/BORSA, CC-04/MLSBi, CC-06/blaZ and CC-07/linezolid resistant, cfr); one Staphylococcus epidermidis (CC-05/linezolid resistant, 23S rRNA mutation); and one Staphylococcus capitis (CC-08/daptomycin non-susceptible). Fifty-one laboratories were asked to report: (i) AST system used; (ii) antimicrobial MICs; (iii) breakpoints used (CLSI or EUCAST); and (iv) clinical category. Minor, major and very major errors (mEs, MEs and VMEs, respectively) were determined., [Results] The greatest MIC discrepancies found were: (i) by AST method: 19.4% (gradient diffusion); (ii) by antimicrobial agent: daptomycin (21.3%) and oxacillin (20.6%); and (iii) by isolate: CC-07/cfr (48.0%). The greatest error rates were: (i) by AST method: gradient diffusion (4.3% and 5.1% VMEs, using EUCAST and CLSI, respectively); (ii) by breakpoint: 3.8% EUCAST and 2.3% CLSI; (iii) by error type: mEs (0.8% EUCAST and 1.0% CLSI), MEs (1.8% EUCAST and 0.7% CLSI) and VMEs (1.2% EUCAST and 0.6% CLSI); (iii) by antimicrobial agent: VMEs (4.7% linezolid and 4.3% oxacillin using EUCAST); MEs (14.3% fosfomycin, 9.1% tobramycin and 5.7% gentamicin using EUCAST); and mEs (22.6% amikacin using EUCAST)., [Conclusions] Clinical microbiology laboratories should improve their ability to determine the susceptibility of Staphylococcus spp. to some antimicrobial agents to avoid reporting false-susceptible or false-resistant results. The greatest discrepancies and errors were associated with gradient diffusion, EUCAST breakpoints and some antimicrobials (mEs for aminoglycosides; MEs for fosfomycin, aminoglycosides and oxacillin; and VMEs for linezolid and oxacillin)., This work was supported by the Instituto de Salud Carlos III, Subdirección General de Redes y Centros de Investigación Cooperativa, Ministerio de Economía y Competitividad and the Spanish Network for Research in Infectious Diseases (REIPI RD 16/0016)—co-financed by the European Development Regional Fund (ERDF) ‘A way to achieve Europe’ and the Programa integral de prevención, control de las infecciones relacionadas con la asistencia sanitaria y uso apropiado de los antimicrobianos (PIRASOA; Junta de Andalucía, Consejería de Salud, Junta de Andalucía).

Background Vancomycin-resistant enterococci (VRE) are a major cause of morbidity and mortality in immunocompromised patients. Tracking the dissemination of VRE strains is crucial to understand the dynamics of emergence and spread of VRE in the hospital setting. Methods Whole genome sequencing (WGS) and phylogenetic analyses were performed to identify dominant VRE strains and potential transmission networks between 35 patients with VRE-positive rectal swabs and their rooms (main rooms and bathrooms) on the leukemia (LKM) and the hematopoietic cell transplant (HCT) floors. Sequence types (STs), drug resistance genes, and patients’ outcomes were also determined. Results A total of 89 VRE strains grouped into 10 different STs, of which newly described STs were isolated from both floors (ST736, ST494, ST772, and ST1516). We observed highly genetically related strains transmitted between rooms, floors, and time periods in an average period of 39 days (ranging from 3 to 90 days). Of 5 VRE bacteremia events, 3 strains were lacking the pili operon fms14–17–13 (ST203) and the remaining 2 were resistant to daptomycin (DAP; ST736, ST664). Of 10 patients harboring DAP-resistant strains, only 2 were exposed to DAP within 4 months before strain recovery. Conclusions Our comparisons of VRE strains derived from the environment and immunocompromised patients confirmed horizontal transfer of highly related genetic lineages of multidrug-resistant (particularly to DAP) VRE strains between HCT and LKM patients and their room environment. Implementing WGS can be useful in distinguishing VRE reservoirs where interventions can be targeted to prevent and control the spread of highly resistant organisms.

Background Bloodstream infections (BSIs) with methicillin-susceptible Staphylococcus aureus (MSSA) are associated with significant morbidity and mortality. Our objective in this study was to determine the efficacy of synergistic treatment with daptomycin when given with either cefazolin or cloxacillin for the treatment of MSSA BSI. Methods A randomized, double-blind, placebo-controlled trial was performed at 2 academic hospitals in Montreal, Canada. Patients aged ≥18 years with MSSA BSI receiving either cefazolin or cloxacillin monotherapy were considered for inclusion. In addition to the standard-of-care treatment, participants received a 5-day course of adjunctive daptomycin or placebo. The primary outcome was the duration of MSSA BSI in days. Results Of 318 participants screened, 115 were enrolled and 104 were included in the intention-to-treat analysis (median age, 67 years; 34.5% female). The median duration of bacteremia was 2.04 days among patients who received daptomycin vs 1.65 days in those who received placebo (absolute difference, 0.39 days; P = .40). In a modified intention-to-treat analysis that involved participants who remained bacteremic at the time of enrollment, we found a median duration of bacteremia of 3.06 days among patients who received daptomycin vs 3.0 days in those who received placebo (absolute difference, 0.06 days; P = .77). Ninety-day mortality in the daptomycin arm was 18.9% vs 17.7% in the placebo arm (P = 1.0). Conclusions Among patients with MSSA BSIs, the administration of adjunctive daptomycin therapy to standard-of-care treatment did not shorten the duration of bacteremia and should not be routinely considered. Clinical Trials Registration NCT02972983.

BackgroundIncreasing application of vancomycin due to the high prevalence of MRSA infections has led to the emergence of vancomycin intermediate-resistant Staphylococcus aureus (VISA) and heterogeneous VISA (hVISA). Consequently, the need for alternative therapies that target MRSA has become evident.ObjectivesTo evaluate the synergy between (lipo)glycopeptides (LGP/GPs) (vancomycin, teicoplanin, telavancin, dalbavancin and oritavancin) and β-lactams (ceftaroline, cefepime, cefazolin and oxacillin) against MRSA, hVISA, VISA and daptomycin non-susceptible (DNS) phenotypes.MethodsTwenty randomly selected clinical MRSA strains (i.e. 5 MRSA, 5 hVISA, 5 VISA and 5 DNS) were assessed versus LGP/GPs alone and LGP/GPs in combination with β-lactams for MICs. Although verification of antibiotic potency against bacterial strains is assessed by the microbroth dilution (MBD) MIC method recommended by the CLSI, some antibiotics need modified assay conditions in order to demonstrate their optimal activity.ResultsAddition of β-lactams reduced MIC values of LGP/GPs against all strains (up to 160-fold reduction). In general, LGPs (dalbavancin, oritavancin and telavancin) were more active (significant differences in MIC values, up to 8-fold) compared with vancomycin and teicoplanin. The majority of these combinations were bactericidal and superior to any single agent.ConclusionsThis report has examined the susceptibility patterns of LGP/GPs and their combination with β-lactams. Of interest, the impact of susceptibility tests (in terms of MIC plates and their surface area) on the synergistic activity in 24 h time–kill experiments was apparent for LGPs. Further clinical research is required to investigate synergy with LGP/GPs and β-lactams against these Staphylococcus strains.

Background The prospective identification of patients at high risk for hospital-acquired/ventilator-associated bacterial pneumonia may improve clinical trial feasibility and foster antibacterial development. In a prior study conducted in the United States, clinical criteria were used to prospectively identify these patients; however, these criteria have not been applied in a European population. Methods Adults considered high risk for pneumonia (treatment with ventilation or high levels of supplemental oxygen) in the intensive care units of 7 European hospitals were prospectively enrolled from June 12 to December 27, 2017. We estimated the proportion of high-risk patients developing pneumonia according to US Food and Drug Administration guidance and a subset potentially eligible for antibacterial trial enrollment. We compared patient characteristics, treatment exposures, and pneumonia incidence in a European cohort and a previously described US cohort. Results Of 888 high-risk patients, 211/888 (24%) were treated for possible pneumonia, and 150/888 (17%) met the Food and Drug Administration definition for hospital-acquired/ventilator-associated bacterial pneumonia. A higher proportion of European patients treated for possible pneumonia met the pneumonia definition (150/211 [71%] vs 537/1464 [37%]; P Conclusions Clinical criteria prospectively identified high-risk patients with high rates of pneumonia in the European cohort. Despite higher rates of established risk factors and incident pneumonia, European patients were significantly less likely to receive antibiotics for possible pneumonia than US patients. Different treatment practices may contribute to lower rates of antibacterial trial enrollment in the United States.

Daptomycin is a cyclic lipopeptide used in the treatment of vancomycin-resistant Enterococcus faecium (VREfm). However, the development of daptomycin-resistant VREfm challenges the treatment of nosocomial VREfm infections. Resistance mechanisms of daptomycin are not fully understood. Here, we analyzed the genomic changes leading to a daptomycin-susceptible VREfm isolate becoming resistant after 50 days of daptomycin and linezolid combination therapy. A total of seven isogenic VREfm isolates from the same patient (daptomycin-susceptible and daptomycin-resistant) were analyzed using Illumina whole genome sequencing, and two isolates were further characterized with Nanopore sequencing. One nonsynonymous SNP in the rpoC gene previously shown to harbor mutations in daptomycin-resistant VREfm was identified in the daptomycin-resistant isolates. Whole genome comparative analysis identified the loss of a 46.5 kb fragment, duplication of a 29.7 kb fragment, and integration of two plasmids upon acquisition of daptomycin resistance. Transmission electron microscopy showed similar alterations in cell morphology and cell wall structure as have previously been described in daptomycin-resistant E. faecalis.

Objectives The dosing regimen of daptomycin for critically ill patients undergoing continuous renal replacement therapy (CRRT) remains controversial. The goal of this study was to provide guidance for optimal daptomycin therapy in CRRT patients with Staphylococcus aureus infections. Methods Individual concentration data of 32 CRRT subjects pooled from previously published studies were used to construct the population pharmacokinetic model for daptomycin. Model-based simulations were performed to evaluate the efficacy and risk of toxicity for daptomycin doses of 4, 6 and 8 mg/kg, q24h or q48h, under CRRT doses of 25, 30 and 35 mL/h/kg. Efficacy was assessed by the bacteriostatic and bactericidal AUC/MIC targets and drug exposure-based efficacy references. Toxicity was estimated by safety exposure references and the trough concentration threshold. Results A two-compartment model adequately described the pharmacokinetics of daptomycin. Efficacy analysis demonstrated that q48h dosing is associated with an extremely low probability of bactericidal target attainment on every second day after dosing and q24h dosing is preferred for a high probability of bactericidal target attainment. Toxicity evaluation showed that 8 mg/kg q24h has a high probability for reaching the toxicity-related concentration threshold, while 6 mg/kg q24h gives a satisfactory risk–benefit balance. The studied CRRT doses had a limited impact on efficacy and a CRRT dose of 30–35 mL/h/kg may lower the risk of toxicity. Conclusions The model predicted that the combination of 6 mg/kg q24h daptomycin dose and CRRT dose of 30–35 mL/h/kg would achieve the best balance of efficacy and safety.

Background Glycopeptides (GPs), lipopeptides (LPs) and lipoglycopeptides (LGPs) are related antimicrobials important for the management of invasive MRSA infections. Cross-resistance among these antibiotics in MRSA is well documented, as is the observation that susceptibility of MRSA to β-lactams increases as susceptibility to GPs and LPs decreases (i.e. the seesaw effect). Efforts to understand the relationship between GP/LP/LGP cross-resistance and the seesaw effect have focused on the PBPs, but the role of lipid metabolism has not been investigated. Objectives Since the cell membrane is structurally and metabolically integrated with the cell wall and anchors associated proteins, including PBPs, we examined the relationship between membrane lipid composition and the phenomena of cross-resistance among GPs/LPs/LGPs and the β-lactam seesaw effect. Methods We selected for daptomycin, vancomycin and dalbavancin resistance using the USA300 strain JE2 and evaluated the resulting mutants by WGS, MS-based lipidomics and antimicrobial susceptibility testing to assess the relationship between membrane composition, cross-resistance, and the seesaw effect. Results We observed cross-resistance to GPs/LPs/LGPs among the selected strains and the seesaw effect against various β-lactams, depending on the PBP targets of the particular β-lactam. We found that modification of membrane composition occurs not only in daptomycin-selected strains, but also vancomycin- and dalbavancin-selected strains. Significantly, we observed that the abundance of most phosphatidylglycerols positively correlates with MICs of GPs/LPs/LGPs and negatively correlates with the MICs of β-lactams. Conclusions These studies demonstrate a major association between membrane remodelling, cross-resistance and the seesaw effect.

Daptomycin (DAP) is key in treating multidrug-resistant Staphylococcus infections. Diminished susceptibility to DAP is emerging among Staphylococcus epidermidis strains although mechanisms for non-susceptibility (NS) remain poorly understood. We report a case of persistent S. epidermidis bacteremia in which loss of DAP susceptibility arose during prolonged treatment. Whole genome sequencing identified two mutations, Q371del and P415L, in a single-affected gene, WalK, that coincided with the emergence of DAP-NS. Protein modeling of the mutations predicted a disruption of WalK protein configuration. The emergence of mutations in a single-gene during DAP exposure raises concerns in an era of increasingly treatment-resistant infections. Lay summary: Daptomycin is an important antibiotic for fighting Staphylococcus infections. We identified variants in the WalK gene that were coincident with resistance in a clinical Staphylococcus epidermidis infection. Clinicians, hospital epidemiologists, and microbiology laboratories need to be aware of the potential for the evolution of drug resistance during prolonged daptomycin therapy.

BackgroundMounting evidence suggests the addition of a β-lactam (BL) to daptomycin (DAP) results in synergistic in vitro activity against methicillin-resistant Staphylococcus aureus (MRSA) and bolsters the innate immune response to infection. This study’s objective was to provide clinical translation to these experimental data and determine if DAP+BL combination therapy results in improved clinical outcomes compared with treatment with DAP alone in patients with MRSA bloodstream infections (BSIs).MethodsThis was a retrospective, comparative cohort study conducted at 2 academic medical centers between 2008 and 2018. Adults with MRSA BSI treated with DAP for ≥72 hours and initiated ≤5 days of culture collection were included. Patients who received a BL for ≥24 hours and initiated ≤24 hours of DAP comprised the DAP+BL group. The primary outcome was composite clinical failure (60-day all-cause mortality and/or 60-day recurrence). Analyses were adjusted for confounding using inverse probability of treatment weighting (IPTW).ResultsA total of 229 patients were included (72 DAP+BL and 157 DAP). In unadjusted and IPTW-adjusted analyses, DAP+BL was associated with significantly reduced odds of clinical failure (odds ratio [OR], 0.362; 95% confidence interval [CI], .164–.801; adjusted OR, 0.386; 95% CI, .175–.853). Adjusted analyses restricted to prespecified subgroups based on infection complexity and baseline health status were consistent with the main analysis.ConclusionsThe addition of a BL to DAP was associated with improved clinical outcomes in patients with MRSA BSI. This study provides support to ongoing and future studies evaluating the impact of combination therapy for invasive MRSA infections.Patients treated with daptomycin plus a β-lactam for MRSA bloodstream infection had lower odds of composite clinical failure defined as 60-day all-cause mortality and/or 60-day recurrence compared with patients treated with daptomycin monotherapy after adjusting for confounding variables using inverse probability of treatment weighting.

Objectives To determine the efficacy of different antibiotics (alone or in combination) against Abiotrophia defectiva and Granulicatella elegans biofilms and to investigate the anti-biofilm activity of gentamicin alone versus blood culture isolates from both species. Methods The activity of benzylpenicillin, clindamycin, daptomycin, fosfomycin, gentamicin, levofloxacin and rifampicin against 24-hour-old biofilms of A. defectiva and G. elegans was investigated in vitro by conventional microbiological methods and isothermal microcalorimetry. Results For planktonic bacteria, the MIC values of tested antibiotics ranged from 0.016 to 64 mg/L, as determined by microcalorimetry. Higher antibiotic concentrations, ranging from 1 to >1024 mg/L, were needed to produce an effect on biofilm bacteria. Gentamicin was an exception as it was active at 1 mg/L against both planktonic and biofilm G. elegans. A synergistic effect was observed when daptomycin was combined with benzylpenicillin, gentamicin or rifampicin against A. defectiva biofilms and when gentamicin was combined with rifampicin or levofloxacin against G. elegans biofilms. A. defectiva clinical isolates displayed greater variability in gentamicin susceptibility as compared with G. elegans strains. Conclusions Antimicrobial susceptibility profiles vary widely between Abiotrophia and Granulicatella biofilms, and synergistic effects of the tested antibiotics were heterogeneous. The clinical relevance of these in vitro observations needs to be confirmed in experimental in vivo conditions and human trials, before guidelines for the treatment of A. defectiva and G. elegans infections are established. This study suggests the benefit of further clinical exploration of antibiotic combinations with anti-biofilm effect.

Antibiotic production during secondary metabolism in Streptomyces spp. is elaborately controlled by multiple environmental signals and intracellular cascades. These include the two-component system PhoRP responding to phosphate starvation and a conserved signaling pathway mediated by the pleiotropic regulator AdpA. However, little information exists about how these two pathways work together for secondary metabolite production of Streptomyces. Herein, we report the dual regulation from the phosphate starvation-responsive regulator PhoP and AdpA on atrA promoter (atrAp) for the production of daptomycin, an antibiotic produced by Streptomyces roseosporus. We found that PhoP directly binds to atrAp, positively regulates atrA expression and thus daptomycin production. We also observed positive auto-regulation of phoRP expression during fermentation for daptomycin production. Moreover, partial overlap between PhoP- and AdpA-binding sites on atrAp was observed, which results in partial competitive binding between these two regulators. This partial overlapping and competition between PhoP and AdpA was further confirmed by mutations and binding assays. In summary, our findings have revealed dual regulation of PhoP and AdpA on the same promoter for antibiotic production in Streptomyces. This mechanism would be beneficial to further environment-responsive fermentation optimization for antibiotic production.

The cyclic lipopeptide antibiotics structurally related to daptomycin were first reported in the 1950s. Several have common lipopeptide initiation, elongation, and termination mechanisms. Initiation requires the use of a fatty acyl-AMP ligase (FAAL), a free-standing acyl carrier protein (ACP), and a specialized condensation (CIII) domain on the first NRPS elongation module to couple the long chain fatty acid to the first amino acid. Termination is carried out by a dimodular NRPS that contains a terminal thioesterase (Te) domain (CAT-CATTe). Lipopeptide BGCs also encode ABC transporters, apparently for export and resistance. The use of this mechanism of initiation, elongation, and termination, coupled with molecular target-agnostic resistance, has provided a unique basis for robust natural and experimental combinatorial biosynthesis to generate a large variety of structurally related compounds, some with altered or different antibacterial mechanisms of action. The FAAL, ACP, and dimodular NRPS genes were used as molecular beacons to identify phylogenetically related BGCs by BLASTp analysis of finished and draft genome sequences. These and other molecular beacons have identified: (i) known, but previously unsequenced lipopeptide BGCs in draft genomes; (ii) a new daptomycin family BGC in a draft genome of Streptomyces sedi; and (iii) novel lipopeptide BGCs in the finished genome of Streptomyces ambofaciens and the draft genome of Streptomyces zhaozhouensis.

Background The management of endocarditis requires aggressive and prolonged antimicrobial treatment. We evaluated the in vitro activity of dalbavancin against bacteria from patients with infective endocarditis. Methods A total of 626 Gram-positive organisms were collected from patients with a diagnosis of bacterial endocarditis in the USA (n = 222) and Europe (n = 404) from 2007 to 2017 via the SENTRY Antimicrobial Surveillance Program and were tested for susceptibility to dalbavancin and comparators by broth microdilution. Results The most common organisms were Staphylococcus aureus (48.4%), Enterococcus faecalis (19.6%) and viridans group streptococci (VGS; 12.5%). Dalbavancin and daptomycin showed complete activity (100.0% susceptibility per CLSI criteria) against S. aureus, but dalbavancin MIC values were 4- to 8-fold lower. Vancomycin, linezolid and teicoplanin were also active against all S. aureus when CLSI criteria were applied. Ceftaroline was active against all MSSA (MIC90 0.25 mg/L) and 78.4% of MRSA isolates at ≤1 mg/L. All E. faecalis isolates were susceptible to ampicillin, daptomycin and linezolid, whereas 97.6% of isolates were susceptible to dalbavancin (MIC90 0.06 mg/L) and 96.7% were susceptible to vancomycin (MIC90 2 mg/L). All VGS and CoNS isolates were susceptible to dalbavancin, daptomycin, vancomycin and linezolid. Against Enterococcus faecium, 65.7% of isolates were inhibited by ≤0.25 mg/L dalbavancin and 62.9% were vancomycin susceptible. Conclusions Dalbavancin exhibited potent in vitro activity against a large collection of Gram-positive isolates recovered from patients with endocarditis in US and European medical centres. These results support further investigations to determine the role of dalbavancin in the treatment of infective endocarditis.

Objectives Prevention of bacterial transmission in recipient patients via allograft decontamination with an antimicrobial cocktail consisting of cefmetazole (cefoxitin), vancomycin, lincomycin and polymyxin B is an important procedure commonly practised in tissue banks. However, some allografts are lost due to the failure of decontamination under low temperature conditions. Here, we aimed to develop new antimicrobial cocktails that exert a high bactericidal activity at 4°C. Methods Bacterial species used in this study were selected as major causative pathogens of allograft tissue contamination. The efficacy of the combination of 2 antimicrobial agents was determined by the checkerboard titration method. The bactericidal effects of the new antimicrobial cocktails were evaluated under the same conditions as those used for the storage and preservation of allograft tissues. Results Among the selected antimicrobial agents, daptomycin exhibited the highest bactericidal activity against methicillin-resistant Staphylococcus aureus under low temperature conditions. The combination of daptomycin + gentamicin and daptomycin + levofloxacin showed a synergistic or additive effect against various bacterial species. The antimicrobial cocktail containing 200 μg/ml of daptomycin, gentamicin and levofloxacin could eradicate ≤104 colony-forming units/ml of methicillin-resistant S. aureus and Enterococcus faecalis, which exhibit a low susceptibility to antimicrobial agents at 4°C for 24 h. Conclusions We have developed a new formula for an antimicrobial cocktail to effectively and sufficiently prevent bacterial contamination of allograft tissues under low temperature conditions in vitro.

OBJECTIVES: Daptomycin non-susceptibility in Staphylococcus aureus can emerge via the accumulation of single or multiple mutations, each resulting in a slight increase in the daptomycin MIC. The daptomycin-non-susceptible phenotype may include other features such as daptomycin tolerance. This study identifies S. aureus genomic regions that frequently develop mutations following prolonged daptomycin exposure but have not been previously associated with daptomycin non-susceptibility. METHODS: Sequence variations in the same eight loci independently observed following 28 day parallel serial passages of S. aureus J01 in daptomycin were introduced in isolation into S. aureus J01. MICs were determined by microbroth dilution. Daptomycin killing and tolerance were determined by kill curve analysis. RESULTS: Single mutations in snoF, hmp1, sspA, rimP, hepT, rsh, map1 and amaP had only a modest impact on the daptomycin MIC (≤2-fold). In contrast, individual mutation in several of these regions resulted in pronounced changes to daptomycin tolerance. CONCLUSIONS: This study demonstrates that less characterized mutations in S. aureus following daptomycin exposure do not result in significant daptomycin susceptibility changes, but rather allow for enhanced survival characteristics during treatment. This sheds new light on genetic adaptations that may play a role in persistent infection. Further studies are needed to elucidate the prevalence of these mutations in clinical isolates.

Background Daptomycin-associated myopathy has been identified in 2%-14% of patients, and rhabdomyolysis is a known adverse effect. Although risk factors for daptomycin-associated myopathy are poorly defined, creatine phosphokinase (CPK) monitoring and temporary discontinuation of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, or "statins," has been recommended. Methods We conducted a single-center, retrospective, matched case-control risk factor analysis in adult and pediatric patients from 2004 to 2015. Patients in whom myopathy (defined as CPK values above the upper limit of normal) developed during daptomycin treatment were matched 1:1 to no-myopathy controls with at least the same duration of therapy. Risk factors independently associated with myopathy were determined using multivariable conditional logistic regression. Secondary analysis was performed in patients with rhabdomyolysis, defined as CPK values ≥10 times the upper limit of normal. Results Of 3042 patients reviewed, 128 (4.2%) were identified as having daptomycin-associated myopathy, 25 (0.8%) of whom had rhabdomyolysis; 121 (95%) of the 128 were adults, and the mean duration of therapy before CPK elevation was 16.7 days (range, 1-58 days). In multivariate analysis, deep abscess treatment (odds ratio, 2.80; P = .03), antihistamine coadministration (3.50; P = .03), and statin coadministration (2.60; P = .03) were independent risk factors for myopathy. Obesity (odds ratio, 3.28; P = .03) and statin coadministration (4.67; P = .03) were found to be independent risk factors for rhabdomyolysis, and older age was associated with reduced risk (0.97; P = .05). Conclusions Statin coadministration with daptomycin was independently associated with myopathy and rhabdomyolysis. This is the first study to provide strong evidence supporting this association. During coadministration, we recommend twice-weekly CPK monitoring and consideration of withholding statins.

Daptomycin is a cyclic lipopeptide antibiotic produced by Streptomyces roseosporus in an acidic peptide complex A21978C. In this complex, A21978C1–3 is most abundant and contains branched-chain fatty acyl groups, while daptomycin has a straight decanoic acyl group. The branched-chain α-keto acid dehydrogenase complex (BCDH complex), encoded by bkd gene clusters in Streptomyces, is responsible for the early step of converting branched-chain amino acids into branched-chain fatty acids. In a daptomycin industrial producer S. roseosporus L30, two alleles of bkd gene clusters, bkdA1B1C1/bkdA2B2C2, and a regulatory gene bkdR located upstream of bkdA2B2C2 are identified. We show that BkdR positively regulated bkdA2B2C2 expression and was negatively auto-regulated, but is not directly involved in regulation of daptomycin gene cluster expression. However, BkdR is required for both daptomycin and A21978C1–3 production. Furthermore, deletion of bkdA2B2C2 only led to partial reduction of A21978C1–3 production, while the ΔbkdA1B1C1 mutant shows very weak production of A21978C1–3, and the double bkd mutant has a similar production profile as the single ΔbkdA1B1C1 mutant, suggesting that bkdA1B1C1 gene cluster plays a dominant role in branched-chain fatty acid biosynthesis. So we reveal a unique regulatory function of BkdR and genetic engineered a bkd null strain for daptomycin production with reduced impurities.

ObjectivesTo evaluate putative anti-staphylococcal biofilm antibiotic combinations used in the management of periprosthetic joint infections (PJIs).MethodsUsing the dissolvable bead biofilm assay, the minimum biofilm eradication concentration (MBEC) was determined for the most commonly used antimicrobial agents and combination regimens against staphylococcal PJIs. The established fractional inhibitory concentration (FIC) index was modified to create the fractional biofilm eradication concentration (FBEC) index to evaluate synergism or antagonism between antibiotics.ResultsOnly gentamicin (MBEC 64 mg/L) and daptomycin (MBEC 64 mg/L) were observed to be effective antistaphylococcal agents at clinically achievable concentrations. Supplementation of gentamicin with daptomycin, vancomycin or ciprofloxacin resulted in a similar or lower MBEC than gentamicin alone (FBEC index 0.25–2). Conversely, when rifampicin, clindamycin or linezolid was added to gentamicin, there was an increase in the MBEC of gentamicin relative to its use as a monotherapy (FBEC index 8–32).ConclusionsThis study found that gentamicin and daptomycin were the only effective single-agent antibiotics against established Staphylococcus biofilms. Interestingly the addition of a bacteriostatic antibiotic was found to antagonize the ability of gentamicin to eradicate Staphylococcus biofilms.

VRE are associated with ∼1300 deaths per year in the USA. Recent literature suggests that daptomycin, a cyclic lipopeptide antibiotic with concentration-dependent bactericidal activity, is the preferred treatment option for VRE bacteraemia, yet the optimal dosing strategy for this indication has not been established. In vitro evidence suggests that higher-than-labelled doses of daptomycin are required to optimally treat VRE bacteraemia and to inhibit the development of resistance. However, concern of dose-dependent toxicities, notably increases in creatine phosphokinase and the development of rhabdomyolysis, are a barrier to initiating high-dose schemes in clinical practice. Thus, the effectiveness and safety of high-dose daptomycin regimens in clinical practice have remained unclear. While early studies failed to identify differences in mortality, newer, larger investigations suggest high-dose (≥9 mg/kg) daptomycin is associated with reduced mortality in patients with VRE bacteraemia compared with standard (6 mg/kg) dosing regimens. Additionally, the high-dose regimens appear to be safe and may be associated with improved microbiological outcomes. The purpose of this review is to examine the published evidence on the effectiveness and safety of high-dose daptomycin compared with standard dosing regimens for VRE bacteraemia.

Background: Enterococcus faecium is an important nosocomial pathogen. It has a high propensity for horizontal gene transfer, which has resulted in the emergence of MDR strains that are difficult to treat. The most notorious of these, vancomycin-resistant E. faecium, are usually treated with linezolid or daptomycin. Resistance has, however, been reported, meaning that new therapeutics are urgently needed. The 1,2,4-oxadiazoles are a recently discovered family of antimicrobials that are active against Gram-positive pathogens and therefore have therapeutic potential for treating E. faecium. However, only limited data are available on the activity of these antimicrobials against E. faecium. Objectives: To determine whether the 1,2,4-oxadiazole antimicrobials are active against MDR and daptomycinnon- susceptible E. faecium. Methods: The activity of the 1,2,4-oxadiazole antimicrobials against vancomycin-susceptible, vancomycin-resistant and daptomycin-non-susceptible E. faecium was determined using susceptibility testing, time-kill assays and synergy assays. Toxicity was also evaluated against human cells by XTT and haemolysis assays. Results: The 1,2,4-oxadiazoles are active against a range of MDR E. faecium, including isolates that display nonsusceptibility to vancomycin and daptomycin. This class of antimicrobial displays rapid bactericidal activity and demonstrates superior killing of E. faecium compared with daptomycin. Finally, the 1,2,4-oxadiazoles act synergistically with daptomycin against E. faecium, with subinhibitory concentrations reducing the MIC of daptomycin for non-susceptible isolates to a level below the clinical breakpoint. Conclusions: The 1,2,4-oxadiazoles are active against MDR and daptomycin-non-susceptible E. faecium and hold great promise as future therapeutics for treating infections caused by these difficult-to-treat isolates.

Purpose The results of a study to determine the physical compatibility of ZTI-01 (fosfomycin for injection) in 0.9% sodium chloride or 5% dextrose during simulated Y-site administration with 37 i.v. antimicrobials and 58 nonantimicrobials are reported. Methods Fosfomycin, an epoxide antibiotic with broad-spectrum activity against multidrug-resistant bacteria, is marketed in the United States only in an oral formulation with limited bioavailability, but an i.v. formulation is in development. Fosfomycin for injection and other evaluated drugs were reconstituted according to manufacturer recommendations and further diluted with 0.9% sodium chloride or 5% dextrose to the final desired concentrations. Y-site administration was simulated in glass culture tubes. Incompatibility was defined as changes in visual characteristics or a change in turbidity of >0.5 nephelometric turbidity units over the 120-minute observation period. Results Of the 95 drugs tested, 16 were incompatible with fosfomycin in 0.9% sodium chloride, and 18 were incompatible with fosfomycin in 5% dextrose; incompatibility was observed with 10 of 37 antimicrobials, including the 3 commercially available amphotericin B products, anidulafungin, caspofungin, ceftaroline, ciprofloxacin, daptomycin, doxycycline, and isavuconazonium sulfate. Conclusion Fosfomycin for injection at a concentration of 30 mg/mL was physically compatible with 73 of 95 (77%) of the i.v. drugs tested at concentrations used clinically in both 0.9% sodium chloride injection and 5% dextrose injection. Twenty-two drugs were deemed incompatible in at least 1 of the 2 diluents.

Ceftaroline is often used in durations greater than that studied in clinical trials. Several retrospective, non-comparative studies have suggested a higher than anticipated incidence of neutropenia in patients receiving prolonged treatment with ceftaroline. We sought to determine if ceftaroline was associated with neutropenia by comparing the incidence with ceftaroline treatment with treatment with several comparative antibiotics.Patients receiving 14 or more consecutive days of treatment with ceftaroline were compared with patients receiving cefazolin, daptomycin, linezolid, nafcillin or vancomycin (control group). The primary outcome was the development of neutropenia. Multivariate logistic regression and propensity score weighting using inverse probability weights with regression adjustment were used to control for confounding variables.A total of 753 patients were included (53 that received ceftaroline and 700 that received a comparative antibiotic). Ceftaroline was associated with a greater incidence of neutropenia as compared with the control group (17.0% versus 3.9%, P 0.001). Several covariates were also associated with neutropenia and included younger age, lower baseline absolute neutrophil count, liver disease and bone and joint infections. After controlling for these confounders, receipt of ceftaroline continued to be associated with the development of neutropenia (adjusted OR 3.97, P = 0.003). Analysis after propensity score weighting confirmed this finding.The results of this study suggest that prolonged treatment with ceftaroline is associated with a greater incidence of neutropenia as compared with other antibiotics that are often used for treatment of staphylococcal infections. Careful monitoring of absolute neutrophil count is recommended in patients receiving14 days of ceftaroline.

Daptomycin is a cyclic lipopeptide antibiotic used for the treatment of Gram-positive infections including complicated skin and skin structure infections, right-sided infective endocarditis, bacteraemia, meningitis, sepsis and urinary tract infections. Daptomycin has distinct mechanisms of action, disrupting multiple aspects of cell membrane function and inhibiting protein, DNA and RNA synthesis. Although daptomycin resistance in Gram-positive bacteria is uncommon, there are increasing reports of daptomycin resistance in Staphylococcus aureus, Enterococcus faecium and Enterococcus faecalis. Such resistance is seen largely in the context of prolonged treatment courses and infections with high bacterial burdens, but may occur in the absence of prior daptomycin exposure. Furthermore, use of inadequate treatment regimens, irregular drug supply and poor drug quality have also been recognized as other important risk factors for emergence of daptomycin-resistant strains. Antimicrobial susceptibility testing of Gram-positive bacteria, communication between clinicians and laboratories, establishment of internet-based reporting systems, development of better and more rapid diagnostic methods and continuous monitoring of drug resistance are urgent priorities.

Aims The wblA gene, encoding a homolog of the WhiB family protein, was identified in the sequenced genome of daptomycin producer S.roseosporus. To explore the function of wblA, we construct wblA disruption strains, complemented strains and overexpression strains to test whether it can affect the production of secondary metabolites and morphogenesis. Methods and results We constructed disruption strains by homologous recombination in S.roseosporus. The disruption mutant of wblA could block aerial mycelium sporulation and enhance the production of daptomycin by 51%. In contrast, overexpression of wblA resulted in significantly decreased the yield of daptomycin. In agreement with it, the transcription of key daptomycin regulatory genes atrA, dptR2 and dptR3 and structural gene dptE remarkably increased in the wblA disruption mutant. Conclusions wblA plays a key role in control of daptomycin biosynthesis and is essential for sporulation. The disruption of wblA could accumulate the transcription level of some key genes involving in daptomycin biosynthesis. Significance and Impact of the Study Daptomycin is an important antibiotic with potent activity against a variety of Gram-positive pathogens. This study demonstrates that valuable improvement in the yield of daptomycin can be achieved through modulating the expression of wblA transcription regulator. This article is protected by copyright. All rights reserved.

Objectives: Among viridans group streptococcal infective endocarditis (IE), the Streptococcus mitis group is the most common aetiological organism. Treatment of IE caused by the S. mitis group is challenging due to the high frequency of β-lactam resistance, drug allergy and intolerability of mainstay antimicrobial agents such as vancomycin or gentamicin. Daptomycin has been suggested as an alternative therapeutic option in these scenarios based on its excellent susceptibility profile against S. mitis group strains. However, the propensity of many S. mitis group strains to rapidly evolve stable, high-level daptomycin resistance potentially limits this approach. Methods: We evaluated the activity of 6 mg/kg/day daptomycin alone or in combination with gentamicin, ceftriaxone or ceftaroline against two daptomycin-susceptible S. mitis group strains over 96 h in a pharmacokinetic/pharmacodynamic model of simulated endocardial vegetations. Results: Daptomycin alone was not bactericidal and high-level daptomycin resistance evolved at 96 h in both organisms. Combinations of daptomycin + ceftriaxone and daptomycin + ceftaroline demonstrated enhanced killing activity compared with each antibiotic alone and prevented emergence of daptomycin resistance at 96 h. Use of gentamicin as an adjunctive agent neither improved the efficacy of daptomycin nor prevented the development of daptomycin resistance. Conclusions: Addition of ceftriaxone or ceftaroline to daptomycin improves the bactericidal activity against S. mitis group strains and prevents daptomycin resistance emergence. Further investigation with combinations of daptomycin and β-lactams in a large number of strains is warranted to fully elucidate the clinical implications of such combinations for treatment of S. mitis group IE.

Background In-vitro studies have shown synergistic bactericidal activity with daptomycin (DAP) plus β-lactam antimicrobials against vancomycin resistant enterococci (VRE). There is a paucity of data regarding clinical outcomes with this combination in VRE bloodstream infections (BSI). The purpose of this study was to assess the efficacy of DAP plus a β-lactam with in-vitro activity vs. other therapies for treatment of VRE BSI. Methods IRB-approved, single-center, retrospective study of patients with VRE BSI from 01/2018-09/2019. Patients were excluded if < 18 years old, pregnant, or incarcerated. The primary outcome was time-to-microbiological clearance. Secondary outcomes included infection-related mortality, 30-day all-cause mortality, and incidence of recurrent BSI within 30 days of index culture. Targeted DAP doses were ≥ 8mg/kg and based on MIC. Factors associated with significance for outcomes, via univariate analysis, were evaluated with multivariable logistic regression (MLR), removed in a backward-step approach. Results A total of 85 patients were included, 23 of which received DAP plus a β-lactam. The comparator arm included linezolid or DAP monotherapy. Patients with combination therapy had significantly higher Charlson Comorbidity Index (CCI) (p=0.013) and numerically higher Pitt Bacteremia scores (PBS) (p=0.087) (Table 1). There was no difference seen in the primary outcome (Table 2). Secondary outcomes are provided in Table 2. The presence of polymicrobial infection and higher PBS were significantly associated with infection-related mortality (p=0.008 and p=0.005, respectively) by MLR. A Mann Whitney U test indicated that presence of infection-related mortality was greater for patients with higher MICS (U=20.5, p=0.06). The presence of an underlying source may be related to recurrence of BSI (p=0.075). Table 1: Patient Characteristics Table 2. Primary and Secondary Outcomes Conclusion We did not find a significant difference in time-to-microbiological clearance, although patients treated with DAP and a β-lactam had higher CCI and PBS. These results are limited by retrospective design, small sample size, and potential selection bias. Prospective randomized studies are needed to further validate these findings. Disclosures All Authors: No reported disclosures

Background CF-296 is a novel lysin in pre-clinical development for the treatment of methicillin-susceptible and methicillin-resistant Staphylococcus aureus infections, used in addition to standard of care antibiotics including VAN and DAP. We evaluated the in vivo efficacy of CF-296 alone and in addition to VAN and DAP against S. aureus. Methods Eight isolates (1 MSSA and 7 MRSA) were studied. Murine ICR MIC (100% serum) and human MIC (100% serum) for CF-296 ranged from 32-256 mg/L to 0.5-1 mg/L respectively. Broth microdilution MICs for DAP ranged from 0.5-1 mg/L while all isolates exhibited a VAN MIC of 1 mg/L. Neutropenic ICR mice were thigh inoculated with bacterial suspensions (107 CFU/mL). Mice were administered three monotherapy regimens subcutaneously (SC) or intravenously (IV): i) sub-therapeutic VAN, SC (i.e., a dose that yielded bacteria stasis or growth in order to evaluate further bacterial killing), ii) sub-therapeutic DAP, SC, or iii) CF-296 50 mg/kg, IV. Combination of sub-therapeutic VAN or DAP in addition to 5 escalating CF-296 doses ranging from 0.5 to 50 mg/kg were also examined. Control mice were vehicle-dosed. Efficacy was measured as the change in mean thigh bacterial density at 24h relative to 0h controls. Results Relative to starting inoculum (5.71 ± 0.27 at 0h), bacterial density in controls increased by +2.49 ± 0.98 log10 CFU/thigh across all 8 strains. On average, VAN, DAP, and CF-296 monotherapy resulted in +0.90 ± 1.21, +1.47 ± 0.80, and +0.87 ± 1.39 log10 CFU/thigh bacteria growth, respectively. In addition to VAN, escalating CF-296 exposures (0.5 – 50 mg/kg) resulted in an augmented dose-response, ranging from bacterial reduction of -0.26 ± 1.10 (with addition of CF-296 0.5 mg/kg) to -1.01 ± 0.41 log10 CFU/thigh (with addition of CF-296 50 mg/kg). Similarly, escalating CF-296 exposures in addition to DAP resulted in an augmented dose-response, ranging from bacterial density of +0.80 ± 1.19 to -0.72 ± 0.59 log10 CFU/thigh. Conclusion Compared with 24h control, VAN, DAP, and CF-296 alone displayed modest CFU reduction while CF-296 synergized with VAN and DAP to cause further bacterial killing highlighting a potential role for CF-296 adjunctive therapy against MSSA and MRSA isolates. Disclosures Cara Cassino, MD, ContraFect Corporation (Employee)ContraFect Corporation (Employee) Dario Lehoux, PhD, ContraFect Corporation (Consultant) Raymond Schuch, PhD, ContraFect Corporation (Employee) David P. Nicolau, PharmD, Cepheid (Other Financial or Material Support, Consultant, speaker bureau member or has received research support.)Merck & Co., Inc. (Consultant, Grant/Research Support, Speaker’s Bureau)Wockhardt (Grant/Research Support)

Background E. faecalis (Efc) isolates are usually susceptible to ampicillin (AMP). AMP-based regimens are the standard of care for enterococcal infections, although other antibiotics are often used as definitive treatment. We thus compared outcomes of patients with cancer and Efc bacteremia treated with AMP-containing (ACR) and non-AMP-containing antibiotic regimens (NACR). Methods A multicenter, prospective, observational cohort study conducted at MD Anderson Cancer Center, Henry Ford Hospital, and Memorial Hermann Health System. Eligible patients were ≥ 18 years old, diagnosed with cancer, and had at least one Efc bloodstream isolate collected from 12/2015 to 12/2018. Patients with polymicrobial infections were excluded. Patients were divided into two groups: i) ACR and ii) NACR. ACR included patients who received AMP at any time during treatment; other antimicrobials were permitted. NACR patients did not receive AMP at any time. The primary outcome compared desirability of outcome ranking (DOOR) between ACR and NACR at day 14. The DOOR consisted of six hierarchical levels: 1 - death; 2 - inpatient without microbiological cure (MC) and with acute kidney injury (AKI); 3 - inpatient without MC and without AKI; 4 - inpatient admitted with MC and with AKI; 5 - inpatient with MC and without AKI; 6 - alive and discharged. Comparison of DOORs between ACR and NACR was performed using inverse probability of treatment weighted (IPTW) ordered logistic regression. Results Seventy-one patients were included (ACR, n = 35; NACR, n = 36). No difference was seen in DOORs at day 14 between ACR and NACR (odds ratio [OR] 1.14, 95% Confidence Interval [CI] 0.45 – 2.92, p=0.78). No difference was observed for all-cause mortality at day 14 (OR 0.6, 95% CI 0.09 – 3.77, p=0.58) or day 30 (OR 0.42, 95% CI 0.09 – 1.94, p=0.27). Patients treated with ACR received a lower median duration of other antibiotics at any point during treatment compared to NACR: daptomycin (2 v 4 days) vancomycin (2 v 4 days), and linezolid (1 v 2 days). Conclusion Patients with cancer and Efc bloodstream infections had similar outcomes when treated with ACR and NACR. ACR were associated with less use of broad-spectrum antimicrobials. Future research should focus on the ecologic impact of use of NACR. Disclosures Marcus Zervos, MD, Melinta Therapeutics (Grant/Research Support) Cesar A. Arias, MD, MSc, PhD, FIDSA, Entasis Therapeutics (Scientific Research Study Investigator)MeMed (Scientific Research Study Investigator)Merck (Grant/Research Support)

Background Vancomycin-resistant Enterococcus faecium (VREfm) are leading causes of bloodstream infections (BSI) in patients (pts) with hematological malignancies (HM). Daptomycin (DAP) is commonly used to treat VRE BSI, but DAP non-susceptibility (DAP-NS) in pts with HM is increasing. Current methods to determine DAP minimum inhibitory concentrations (MICs) have poor reproducibility. DAP triggers the LiaFSR cell membrane stress response pathway, resulting in the extracellular release of the protein LiaX, a novel protein that functions as a regulator of the membrane response. We postulated that detection of extracellular LiaX correlates with DAP-NS in clinical strains of VREfm. Methods We used 6 well-characterized VREfm BSI isolates (2 DAP-S, 4 DAP-NS) as reference strains to optimize a whole-cell indirect enzyme-linked immunosorbent assay (ELISA) method for LiaX detection. We assessed limit of detection and reproducibility of the ELISA LiaX method. We then assessed 54 clinical VREfm BSI isolates from pts with cancer for validation. We determined DAP MICs by broth microdilution (BMD). We collected clinical and microbiological details by chart review Results The 6 reference strains showed high reproducibility with low coefficient of variation. All DAP-NS reference strains had increased detection of LiaX (p< 0.0001) compared to DAP-S reference strains. Of the 54 isolates from pts, most pts (83.3%) had HM. The source of 62.9% of VRE BSIs was determined to be gastrointestinal. Six of the 54 isolates were DAP-NS by BMD MIC. The LiaX test and MIC had categorical agreement on 56% of isolates. Of the isolates with disagreement, 19 isolates were susceptible by MIC (median 2 μg/ml) but non-susceptible by LiaX ELISA, and 5 isolates were non-susceptible by MIC (6, 8, 8, 8, and 16 μg/ml, respectively) but susceptible by LiaX ELISA. Whole-cell indirect LiaX ELISA A405nm of Efm reference strains shows ability to differentiate DAP susceptible MICs from DAP resistant MICs. DAP susceptible (MIC=2 μg/ml) Efm strains are shown in green and DAP resistant (MIC≥8 μg/ml) strains in red. DAP-S reference strains have no LiaFSR mutations. The dotted line indicates an example cutoff for DAP-S/R in this assay. *p Conclusion Detection of extracellular LiaX has important discrepancies with DAP MIC. Interestingly, LiaX may be a surrogate marker to detect strains with heightened DAP-mediated cell membrane response and potentially identify strains predisposed to DAP therapy failure. Further characterization of the discrepant isolates by genomic analyses and time-kill assays are warranted to fully validate the performance of LiaX ELISA. Disclosures Cesar A. Arias, MD, MSc, PhD, FIDSA, Entasis Therapeutics (Scientific Research Study Investigator)MeMed (Scientific Research Study Investigator)Merck (Grant/Research Support)

Background Vancomycin and daptomycin are commonly used in outpatient parenteral antimicrobial therapy (OPAT) for patients requiring lengthy courses of intravenous antimicrobials who are otherwise stable for discharge. Balancing the convenience and cost-savings of OPAT with the potential for adverse effects is challenging, this study compared the rates of complications and antimicrobial interventions for patients receiving vancomycin versus daptomycin across multiple OPAT settings. Methods We performed a retrospective chart review of adult OPAT patients who received >72 hours of vancomycin or daptomycin via home infusion, infusion center, or skilled nursing facility between January 2017 and August 2019. The outcomes evaluated included the rates of adverse drug reactions (ADRs), laboratory results above a defined threshold (vancomycin levels >20 mg/mL in the vancomycin arm and creatinine phosphokinase (CPK) levels >500 units/L in the daptomycin group), line complications, emergency department (ED) visits, and hospital readmissions. Other outcomes included additional phone calls and interventions required to coordinate care (additional labs, assessment of symptoms, additional test or antimicrobial-related dose changes) by the OPAT team. Results 180 patients were included; 130 received vancomycin and 50 received daptomycin. (Table 1) Patients in the vancomycin group had more supratherapeutic vancomycin troughs than elevated CPK for patients in the daptomycin group (rate ratio [RR] 0.16, 95% CI 0.05-0.50, p=0.0018). Rates of interventions (RR 0.37, 95% CI 0.26-0.52, p< 0.0001) and additional phone calls (RR 0.56, 95% CI 0.43-0.72, p< 0.0001) were also higher for patients in the vancomycin group. There were no statistically significant differences between groups in the rates of ADRs, line complications, ED visits, or hospital readmissions. (Table 2) Table 1. Baseline Characteristics Table 2. Outcomes Conclusion Vancomycin-treated patients had significantly more laboratory abnormalities and required significantly more time in patient care coordination by the OPAT team. The difference in healthcare utilization between these groups suggests a potential for significant cost-savings for OPAT patients and the healthcare system. Disclosures All Authors: No reported disclosures

This is a single-center retrospective observational cohort study comparing daptomycin/ceftaroline combination therapy with rifampin-adjunct therapy for the treatment of staphylococcal device infections. The results of this study support use of the daptomycin/ceftaroline as an alternative or salvage option to standard of care.

Background Daptomycin and ceftaroline (DAP-CPT) have been used for persistent methicillin-resistant Staphylococcus aureus bacteremia (MRSAB), but have rarely been compared with other therapies. This study provides an exploratory analysis of patients placed on DAP-CPT vs standard of care (SOC) for MRSAB. Methods This is a retrospective, matched cohort study MRSAB patients at 4 hospitals in the United States. Patients receiving DAP-CPT for ≥72 hours at any point in therapy were matched 2:1 when possible, 1:1 otherwise, to SOC, first by infection source, then age and renal function. SOC was empiric treatment with vancomycin or daptomycin and any subsequent combination antibiotic(s), except for DAP-CPT. Results Fifty-eight patients received DAP-CPT with 113 matched SOC. Ninety-six percent of SOC received vancomycin, and 56% (63/113) escalated therapy at least once in the treatment course. Twenty-four patients received DAP-CPT within 72 hours of index culture; 2 (8.3%) died within 30 days vs 14.2% (16/113) with SOC (P > .05). Subgroup analysis identified numerically lower mortality in DAP-CPT patients with a Charlson comorbidity index ≥3, endovascular source, and receipt of DAP-CPT within 72 hours of index culture. The median MRSAB duration was 9.3 vs 4.8 days for DAP-CPT and SOC, respectively. DAP-CPT was initiated on day 6 on average; after receipt of DAP-CPT, MRSAB duration was 3.3 days. Conclusions DAP-CPT treatment is often delayed in MRSAB. Combination therapy may be more beneficial if initiated earlier, particularly in patients at higher risk for mortality. Blinded, randomized, prospective studies are needed to eliminate selection bias inherent in retrospective analyses when examining DAP-CPT vs SOC., This multicenter, retrospective, exploratory, matched study compares demographics and clinical outcomes of patients receiving daptomycin plus ceftaroline at any time in treatment course versus other therapy for MRSA bacteremia. This combination used within 72 hours of index culture may be more beneficial for survival than as salvage therapy.

Daptomycin is one of the few treatment options for infections caused by enterococci that are resistant to ampicillin and vancomycin, such as vancomycin-resistant Enterococcus faecium. The emergence and clinical significance of daptomycin-resistant enterococci and evolving microbiologic, pharmacokinetic-pharmacodynamic, and clinical data indicated that the pre-2019 Clinical and Laboratory Standards Institute (CLSI) susceptible-only breakpoint of ≤4 μg/mL for daptomycin and enterococci was no longer appropriate. After analyzing data that are outlined in this article, the CLSI Subcommittee on Antimicrobial Susceptibility Testing established new breakpoints for daptomycin and enterococci. For E. faecium, a susceptible dose-dependent (SDD) breakpoint of ≤4 μg/mL was established based on an increased dosage of 8–12 mg/kg/day (≥8 μg/mL-resistant). CLSI suggests infectious diseases consultation to guide daptomycin use for the SDD category. For Enterococcus faecalis and other enterococcal species, revised breakpoints of ≤2 μg/mL-susceptible, 4 μg/mL-intermediate, and ≥8 μg/mL-resistant were established based on a standard dosage of 6 mg/kg/day.

Pathogenic strains of Enterococcus cecorum (EC) expressing multidrug resistance have emerged. In National Antimicrobial Resistance Monitoring System (NARMS) data, EC is rarely recovered from chickens. Two NARMS methodologies (FDA and USDA) were compared with standard culture (SC) techniques for recovery of EC. NARMS methods failed to detect EC in 58 caecal samples, 20 chicken breast or six whole broiler samples. EC was recovered from 1 of 38 (2·6%) and 2 of 38 (5·2%) preharvest spinal lesions (USDA and FDA method, respectively). In contrast, using the SC method, EC was recovered from 44 of 53 (83%) caecal samples, all 38 (100%) spinal lesions, 14 of 20 (70%) chicken breast samples, and all three spinal lesions identified in whole carcasses. Compared with other Enterococcus spp., EC isolates had a higher prevalence of resistance to macrolides. The NARMS methods significantly affected recovery of enterococcal species other than EC. When the postharvest FDA method was applied to preharvest caecal samples, isolates of Enterococcus faecium were preferentially recovered. All 11 E. faecium isolates were multidrug resistant, including resistance to penicillin, daptomycin and linezolid. These findings confirm that current methodologies may not accurately identify the amount and range of antimicrobial resistance of enterococci from chicken sources. Significance and Impact of the Study Enterococci are an important reservoir for antimicrobial resistance. This study demonstrates how current culture methods underreport resistance to macrolides in enterococci by selecting against strains of Enterococcus cecorum in pre- and postharvest chicken. Further, the application of postharvest surveillance methods to preharvest samples resulted in selective recovery of Enterococcus faecium over Enterococcus faecalis. Isolates of E. faecium recovered exhibited multidrug resistance including penicillin, daptomycin and linezolid resistance. These findings suggest that culture methodology significantly impacts the range and amount of antimicrobial resistance detected in enterococci isolated from chicken.

Background Treatment options for vancomycin-resistant enterococci (VRE) bloodstream infection (BSI) are limited. Daptomycin, although not currently approved for this indication, is frequently used for the treatment of VRE-BSI. Its optimal dose still needs to be determined. Methods We conducted a prospective, observational, cohort study during 2010-2015. We included patients who received a daptomycin dose of ≥6 mg/kg for the treatment of VRE-BSI caused by daptomycin-susceptible VRE. The primary endpoint was 14-day mortality, and multivariable logistic regression was performed for outcome analysis. Results We included 112 patients treated with daptomycin for VRE-BSI and with evaluable clinical outcomes. The daptomycin minimum inhibitory concentration (MIC) was 4 mg/L in 78 (69.6%) and ≤2 mg/L in 34 (30.4%) isolates. The overall mortality was 40/112 (35.7%). The unadjusted mortality was 18/36 (50.0%) for a daptomycin dose of

Infections by Gram-positive pathogens pose a public health risk, especially due to increasing antibiotic resistance. Daptomycin has efficacy against most clinically important Gram-positive bacteria. Although experience regarding use of daptomycin in adults is increasing, studies on pediatric populations are limited. We aimed to evaluate the efficacy, safety, and pharmacokinetics of daptomycin in pediatric settings. We searched MEDLINE and Clinicaltrials.gov (through April 2016) and included 29 original studies in the final analysis. Available evidence suggests that daptomycin in pediatric patients has a favorable safety and tolerability profile and is an efficacious alternative for treatment of Gram-positive bacteremia, endocarditis, and infections of the skin, soft tissues, joints, and bones, especially when resistant strains are involved. However, future studies need to address several issues to determine the optimal dose and various pharmacokinetic parameters in different pediatric age groups.

BACKGROUND In small series or individual reports, SNPs within the mprF ORF and dysregulation of its expression in Staphylococcus aureus have been linked to daptomycin resistance (DAP-R) via a proposed gain-in-function mechanism. Similarly, dysregulation of dltABCD has also been associated with DAP-R. METHODS Using 22 well-characterized, isogenic daptomycin-susceptible (DAP-S)/DAP-R clinical MRSA strain pairs, we assessed potential relationships of the DAP-R phenotype with: (i) regulation of mprF transcription; (ii) regulation of dltABCD transcription; (iii) expression of the two-component regulatory system, graRS (upstream regulator for both mprF and dltABCD transcription); (iv) SNPs within the graRS promoter or its ORF; and (v) altered mprF transcription and lysyl-phosphatidylglycerol (L-PG) synthesis. RESULTS Enhanced expression of mprF occurred with SNPs in highly distinct and well-chronicled MprF domain 'hot spots' and rarely occurred without such mutations. Increased expression and/or dysregulation of mprF and dltABCD were not uncommon in DAP-R strains, occurring in 27% of strains for each gene. In these latter strains, neither graRS expression profiles nor polymorphic sequences within the graRS promoter or ORF could be significantly linked to altered transcription of mprF or dlt. CONCLUSIONS Although graRS can co-regulate mprF and dltABCD expression, loci outside of this regulon appear to be involved in dysregulation of these latter two genes and the DAP-R phenotype. Finally, DAP-R strains exhibiting significantly altered mprF transcription profiles produced significantly increased levels of L-PG.

Background We report a patient case of methicillin-resistant Staphylococcus aureus (MRSA) bacteremia which over 30 days developed resistance to all three primary antistaphylococcal antibiotics. Index blood cultures displayed susceptibility to vancomycin (VAN, MIC=1), ceftaroline (CPT, MIC=0.5) and daptomycin (DAP, MIC=0.5). The patient was maintained on VAN/CPT with negative blood cultures by hospital day 7. The regimen was later modified to DAP/piperacillin-tazobactam. One month after initial presentation, during the same encounter, blood cultures were again positive for MRSA, now displaying intermediate resistance to VAN (MIC=2) and CPT (MIC=2), and resistance to DAP (MIC=4). Methods Isolates were collected from the initial bacteremia episode (B325) and the recurrence (B326). In-vitro one-compartment pharmacokinetic/pharmacodynamic modeling was performed on each isolate to determine which antibiotics or combinations would effectively eradicate cultures. Regimens examined included DAP (10mg/kg), DAP/cefazolin (CFZ), VAN/CFZ and penicillin/clavulanate. Draft whole-genome sequences are pending for each clinical isolate using hybrid assembly (Unicycler v0.4.2) of MinION and Illumina (150bp PE) reads. Results DAP/CFZ combination reduced viability of both B325 and B326 below limit of detection by 12 hours and maintained efficacy for 72 h. DAP, initially effective in reducing B326 cell concentrations below limit of detection, allowed regrowth by 36 h. All other modeled therapies were less effective. Interestingly, DAP took significantly longer to kill B325 relative to S. aureus collected contemporaneously from other patients. For DAP-containing regimens, the time to 3-log viability reduction (MDK99.9) was five-fold longer in B325 compared to similar clinical isolates with the same DAP MIC. Comparative genomics of sequential isolates is pending, although single nucleotide polymorphisms in vraT and mprF were identified in B326 compared to B325. Conclusion Delayed kill kinetics of B325 when exposed to DAP may indicate antibiotic tolerance, which could partially account for B325’s rapid transition to a multi-drug resistant organism. DAP/CFZ therapy appears to be the most active combination against both antibiotic-tolerant and multidrug resistant S. aureus strains. Disclosures All Authors: No reported disclosures

Background Vancomycin has been the mainstay of treatment for methicillin-resistant Staphylococcus aureus (MRSA) infective endocarditis (IE). MRSA reduced susceptibility to vancomycin is a growing threat. Data assessing the effect of vancomycin reduced susceptibility on outcomes is limited. Our study aimed to evaluate characteristics and outcomes of MRSA-related IE based on the minimum inhibitory concentration (MIC) to vancomycin Characteristics and outcomes of 51 patients with MRSA-related endocarditis according to the minimal inhibitory concentration (MIC) to vancomycin Methods IRB approval was obtained for a retrospective cohort study at a tertiary care center. Records of hospitalized adults diagnose with IE by ICD-9/ICD-10 CM codes were identified from 2011 to 2018. 51 patients had MRSA-related IE and were selected for the analysis. Demographic, microbiologic, Imaging and outcome variables were obtained. Characteristics and outcomes of patients with MRSA-related IE according to the MIC to vancomycin (≤ vs. > 1 mcg/mL) were compared Results 35.3% of patients had a MIC > 1 mcg/mL. 59% were men, mean age was 46±3 years old. 65% acquired the infection through injection drug use. Only 3.9% of patients had prosthetic valve IE. 35.3% had tricuspid valve vegetation, 25.5% mitral valve and 21.6% aortic valve vegetation. Two patients had IE possibly related to a PICC-line infection; both of these patients had a MIC to vancomycin >1 mcg/mL, suggestive of prolonged antibiotic therapy. All patients with MRSA-related IE were started empirically on vancomycin. Patients with a MIC > 1 mcg/mL were more likely to be switched to a combination of daptomycin and ceftaroline, compared to those with a MIC ≤ 1 mcg/mL (44.4% vs. 6.1%; P=0.001). 25.4% underwent valvular replacement within 6 months. 12% died within 90 days. MRSA-related IE with MIC > 1mcg/mL did not confer and an increase risk in in-hospital mortality (11.1% vs. 15.2%; P=0.67) or mortality at 90 days (11.1% vs. 12.5%; P=0.89). Conclusion In this single-center experience, we found that in 8 years 35% of patients with MRSA-related IE had MIC >1 mcg/mL. This is an alarming finding. Although our study did not reach statistic significance we didn’t found difference in valvular surgery requirement or mortality among those with MIC > 1mcg/d as compared to those with a more sensitive MRSA strain. A study with more power or a metha-analysis will be require to better answer this question. Disclosures All Authors: No reported disclosures

Background Prolonged systemic antibiotic courses are frequently used to manage difficult-to-treat bone and joint infections (BJI). Tedizolid has been considered as a therapy candidate for BJI in adults and children. This study assessed the in vitro activity of tedizolid and comparator agents against a contemporary collection of Gram-positive (GP) isolates causing BJI in the US. Methods A total of 310 Staphylococcus aureus (SA), 79 β-hemolytic streptococci (BHS), 52 coagulase-negative staphylococci (CoNS), and 37 Enterococcus faecalis isolates were included in this study. These isolates were collected from patients with BJI from 30 medical centers in the US between 2015 and 2019 as a part of the Surveillance of Tedizolid Activity and Resistance (STAR) Program. Bacterial identification was confirmed by MALDI-TOF MS. MIC results were obtained by reference CLSI broth microdilution methods and interpretations used CLSI guidelines. Results Tedizolid (MIC50/90, 0.12/0.25 mg/L) inhibited all SA at the CLSI breakpoint (≤0.5 mg/L) including methicillin-resistant SA (MRSA; 35.8% of SA; MIC50/90, 0.12/0.25 mg/L). Linezolid, vancomycin, and daptomycin had 100% susceptibility rates against SA isolates (Table). All CoNS isolates were inhibited by tedizolid at ≤0.5 mg/L. Tedizolid was active against all BHS (100% susceptible) as follows: S. pyogenes (n=24; MIC50/90, 0.12/0.25 mg/L), S. agalactiae (n=44; MIC50/90, 0.12/0.25 mg/L), and S. dysgalactiae (n= 11; MIC50/90, 0.25/0.25 mg/L). Penicillin, linezolid, vancomycin, and daptomycin also were active against BHS (100% susceptible). Tedizolid (MIC50/90, 0.25/0.25 mg/L; 100% susceptible) was 4- to 8-fold more potent than linezolid (MIC50/90, 1/1 mg/L) and vancomycin (MIC50/90, 1/2 mg/L) against E. faecalis. GP isolates resistant to oxazolidinone were not observed. Conclusion Tedizolid demonstrated potent in vitro activity against this collection of contemporary GP isolates causing BJI in US hospitals. Tedizolid and comparator agents showed high susceptibility rates against the most frequent organisms and organism groups, including MRSA. These findings support the clinical development of tedizolid as an additional option for treating BJI caused by GP pathogens. Table 1 Disclosures Cecilia G. Carvalhaes, MD, PhD, A. Menarini Industrie Farmaceutiche Riunite S.R.L. (Research Grant or Support)Allergan (Research Grant or Support)Cidara Therapeutics (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Fox Chase Chemical Diversity Center (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Merck (Research Grant or Support)Merck (Research Grant or Support)Merck & Co, Inc. (Research Grant or Support)Pfizer (Research Grant or Support) Helio S. Sader, MD, PhD, A. Menarini Industrie Farmaceutiche Riunite S.R.L. (Research Grant or Support)Allergan (Research Grant or Support)Allergan (Research Grant or Support)Allergan (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Melinta (Research Grant or Support)Merck (Research Grant or Support)Merck (Research Grant or Support)Paratek Pharma, LLC (Research Grant or Support)Pfizer (Research Grant or Support) Jennifer M. Streit, BS, A. Menarini Industrie Farmaceutiche Riunite S.R.L. (Research Grant or Support)A. Menarini Industrie Farmaceutiche Riunite S.R.L. (Research Grant or Support)Allergan (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Merck (Research Grant or Support)Paratek Pharma, LLC (Research Grant or Support) Mariana Castanheira, PhD, 1928 Diagnostics (Research Grant or Support)A. Menarini Industrie Farmaceutiche Riunite S.R.L. (Research Grant or Support)Allergan (Research Grant or Support)Allergan (Research Grant or Support)Amplyx Pharmaceuticals (Research Grant or Support)Cidara Therapeutics (Research Grant or Support)Cidara Therapeutics (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Fox Chase Chemical Diversity Center (Research Grant or Support)GlaxoSmithKline (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Merck (Research Grant or Support)Merck (Research Grant or Support)Merck & Co, Inc. (Research Grant or Support)Merck & Co, Inc. (Research Grant or Support)Paratek Pharma, LLC (Research Grant or Support)Pfizer (Research Grant or Support)Qpex Biopharma (Research Grant or Support) Rodrigo E. Mendes, PhD, A. Menarini Industrie Farmaceutiche Riunite S.R.L. (Research Grant or Support)Allergan (Research Grant or Support)Allergan (Research Grant or Support)Basilea Pharmaceutica International, Ltd (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Department of Health and Human Services (Research Grant or Support)GlaxoSmithKline (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Merck (Research Grant or Support)Merck (Research Grant or Support)Pfizer (Research Grant or Support)

BackgroundVancomycin-resistant enterococcus (VRE) causes substantial health care–associated infection with increasing reports of resistance to daptomycin or linezolid. We conducted a case–control study reporting 81 cases of daptomycin and linezolid–nonsusceptible VRE (DLVRE), a resistance pattern not previously reported.MethodsWe reviewed VRE isolates from June 2010 through June 2015 for nonsusceptibility to both daptomycin (minimum inhibitory concentration [MIC] > 4) and linezolid (MIC ≥ 4). We matched cases by year to control patients with VRE susceptible to both daptomycin and linezolid and performed retrospective chart review to gather risk factor and outcome data.ResultsWe identified 81 DLVRE cases. Resistance to both daptomycin and linezolid was more common than resistance to either agent individually. Compared with susceptible VRE, DLVRE was more likely to present as bacteremia without focus (P < 0.01), with DLVRE patients more likely to be immune suppressed (P = .04), to be neutropenic (P = .03), or to have had an invasive procedure in the prior 30 days (P = .04). Any antibiotic exposure over the prior 30 days conferred a 4-fold increased risk for DLVRE (odds ratio [OR], 4.25; 95% confidence interval [CI], 1.43−12.63; P = .01); multivariate analysis implicated daptomycin days of therapy (DOT) over the past year as a specific risk factor (OR, 1.10; 95% CI, 1.01−1.19; P = .03). DLVRE cases had longer hospitalizations (P = .04) but no increased risk for in-hospital death.ConclusionsDLVRE is an emerging multidrug-resistant pathogen associated with immune suppression, neutropenia, and recent invasive procedure. Prior antibiotic exposure, specifically daptomycin exposure, confers risk for acquisition of DLVRE.