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Background: Daptomycin non-susceptible Staphylococcus aureus (DNS) strains pose a serious clinical threat, yet their characteristics remain poorly understood. Methods: DNS derivatives were generated by exposing S. aureus strains to subinhibitory concentrations of daptomycin. Competition experiment and growth kinetics experiment were used to observe the growth of bacteria. Galleria mellonella larvae and mouse skin abscess models were used to observe the virulence of bacteria. Transmission electron microscopy (TEM), cytochrome C experiment and biofilm formation experiment were used to observe the drug resistance phenotype. And homologous recombination was used to study the role of mutations. Results: Phenotypic profiling of DNS strains revealed impaired growth, increased cell wall thickness, enhanced biofilm formation, reduced negative surface charge, and attenuated virulence compared to their wild-type strains. Whole genome sequencing identified mutations in mprF , cls2 , and saeR in DNS strains. Allelic replacement experiments validated the roles of MprF L341F and Cls2 F60S substitutions in augmenting daptomycin non-susceptibility in Newman. Deletion of saeR in the NewmanMprFL341F strain and complementation of saeR in the Newman-DNS strain did not directly alter daptomycin susceptibility. However, the deletion of saeR was found to enhance competitive fitness under daptomycin pressure. Conclusion: This work validates adaptive laboratory evolution (ALE) for modeling clinical DNS strains and uncovers contributions of mprF , cls2 , and saeR mutations to the adaptation and resistance mechanisms of S. aureus against daptomycin. These findings enrich our understanding of how S. aureus acquired resistance to daptomycin, thus paving the way for the development of more effective treatment strategies and offering potential molecular markers for resistance surveillance. [ABSTRACT FROM AUTHOR]

Background Daptomycin stands as a key IV antibiotic in treating MRSA infections. However, patients facing challenges with difficult venous access require alternative administration routes. This study aimed to evaluate the pharmacokinetic (PK) profile and safety of subcutaneous (SC) daptomycin. Patients and methods In a two-period, two-treatment, single-blind crossover Phase I trial (ClinicalTrials.gov NCT04434300), participants with no medical history received daptomycin (10 mg/kg) both IV and SC in a random order, with a minimum 2 week washout period together with matched placebo (NaCl 0.9%). Blood samples collected over 24 h facilitated PK comparison. Monte Carlo simulations assessed the PTA for various dosing regimens. Adverse events were graded according to Common Terminology Criteria for Adverse Events(CTCAE) v5.0. Results Twelve participants (aged 30.9 ± 24.4 years; 9 male,75%) were included. SC daptomycin exhibited delayed (median T max 0.5 h for IV versus 4 h for SC) and lower peak concentration than IV (C max = 132.2 ± 16.0 μg/mL for IV versus 57.3 ± 8.6 μg/mL for SC; P  < 0.001). SC AUC0–24 (937.3 ± 102.5 μg·h/mL) was significantly lower (P  = 0.005) than IV AUC0–24 (1056.3 ± 123.5 μg·h/mL) but was deemed bioequivalent. PTA demonstrated target AUC0–24 attainment for 100% of simulated individuals, for both 8 and 10 mg/kg/24 h SC regimens. Adverse events (AEs) related to SC daptomycin were more frequent than for SC placebo (25 versus 13, P  = 0.016). No serious AEs were reported. Conclusions Single-dose SC daptomycin infusion proved to be safe, exhibiting a bioequivalent AUC0–24 compared with the IV route. The SC route emerges as a potential and effective alternative when IV administration is not possible. [ABSTRACT FROM AUTHOR]

Staphylococcus aureus (SA) is a leading cause of bloodstream infection. The liver represents the sentinel immune organ for clearance of bloodstream pathogens and eradication of intracellular SA from liver-resident macrophages (Kupffer cells, KCs) eliminates the likely pathogenic reservoir that contributes to persistent bacteraemia. Objectives We assessed antimicrobial activity at phagolysosome-mimicking pH, intracellular penetration, and SA eradication within KCs in vitro for clinically prescribed antistaphylococcal agents alone or in combination: vancomycin, daptomycin, ceftaroline, ceftobiprole, oritavancin, oxacillin, cefazolin; rifampin and fosfomycin. Methods pH-adjusted broth microdilution assays, intracellular bioaccumulation assays, and intracellular killing assays against clinical bloodstream isolates were performed using a murine KC line with study agents. Results Rifampin and β-lactams exhibited enhanced activity [2- to 16-fold minimum inhibitory concentrations (MIC) decrease] at phagolysosomal pH while vancomycin, oritavancin, daptomycin and fosfomycin demonstrated reduced activity (2- to 32-fold MIC increase in order of least to greatest potency reduction). All agents evaluated had poor to modest intracellular to extracellular concentration ratios (0.024–7.8), with exceptions of rifampin and oritavancin (intracellular to extracellular ratios of 17.4 and 78.2, respectively). Finally, we showed that the first-line treatment for SA bacteraemia (SAB), vancomycin, performed worse than all other tested antibiotics in eradicating intracellular SA at human C max concentration (0.20 log cfu decrease), while oritavancin performed better than all other agents alone (2.05 versus 1.06–1.36 log cfu decrease). Conclusions Our findings raise concerns about the efficacy of commonly prescribed antibiotics against intracellular SA reservoirs and emphasize the need to consider targeting pathogen eradication from the liver to achieve early control of SAB. [ABSTRACT FROM AUTHOR]

AbstractA two-compartmental mathematical pharmacokinetic model with first-order elimination of patients receiving CAPD of 4 exchanges for 6 h with 2 L of dialysate used in each cycle was developed to predict daptomycin disposition in 120 h of therapy. The pharmacodynamic target was plasma AUC/MIC equal to or greater than 666. The dose that achieved at least 90% of the probability of target attainment was defined as an optimal dose. Administering intraperitoneal 300 mg daily for 1 exchange daily regimen would be sufficient to treat peritonitis with S. aureus infection with MICs of 0.25 mg/L in patients undergoing CAPD. A higher dosage may be required for infections with a higher minimum inhibitory concentration. Pharmacodynamic targets and MICs significantly contributed to daptomycin doses in this setting. Clinical validation of our recommendations is recommended. [ABSTRACT FROM AUTHOR]

Precision daptomycin dosing faces clinical implementation barriers despite known exposure-safety concerns with the use of twice the regulatory-approved doses. We propose achieving a single 7–11-hour post-dose plasma target concentration of 30 mg/L to 43 mg/L to be a practical starting point to facilitate precision daptomycin dosing. [ABSTRACT FROM AUTHOR]

Background: The increasing prevalence of methicillin-resistant Staphylococcus aureus (MRSA) strains resistant to non-beta-lactam antimicrobials poses a significant challenge in treating severe MRSA bloodstream infections. This study explores resistance development and mechanisms in MRSA isolates, especially after the first dalbavancin-resistant MRSA strain in our hospital in 2016. Methods: This study investigated 55 MRSA bloodstream isolates (02/2015–02/2021) from the University Hospital of the Medical University of Vienna, Austria. The MICs of dalbavancin, linezolid, and daptomycin were assessed. Two isolates (16–33 and 19–362) resistant to dalbavancin were analyzed via whole-genome sequencing, with morphology evaluated using transmission electron microscopy (TEM). Results: S.aureus BSI strain 19–362 had two novel missense mutations (p.I515M and p.A606D) in the pbp2 gene. Isolate 16–33 had a 534 bp deletion in the DHH domain of GdpP and a SNV in pbp2 (p.G146R). Both strains had mutations in the rpoB gene, but at different positions. TEM revealed significantly thicker cell walls in 16–33 (p < 0.05) compared to 19–362 and dalbavancin-susceptible strains. None of the MRSA isolates showed resistance to linezolid or daptomycin. Conclusion: In light of increasing vancomycin resistance reports, continuous surveillance is essential to comprehend the molecular mechanisms of resistance in alternative MRSA treatment options. In this work, two novel missense mutations (p.I515M and p.A606D) in the pbp2 gene were newly identified as possible causes of dalbavancin resistance. [ABSTRACT FROM AUTHOR]

Introduction: Daptomycin (DAP) is a cyclic lipopeptide that exhibits potent in vitro activity against many drug-resistant gram-positive organisms, including methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE). Despite substantial reports evaluating the clinical outcomes of DAP within the adult population, real-world data are lacking in children. The primary goal of this evaluation was to describe the clinical characteristics and outcomes of DAP use in pediatric patients across a wide range of infections. Methods: This retrospective evaluation included patients < 18 years of age who were treated with DAP from January 2014 to May 2023. The primary objective was to evaluate the composite clinical success, which was defined as a 30-day survival, the lack of a 30-day microbiological recurrence, and the resolution of signs and symptoms of an acute infection without therapy modifications based on clinical failures. Secondary objectives included adverse effects potentially attributable to DAP and reasons for DAP utilization. Results: Forty patients were included, which were predominately male (62.5%) and white (52.5%), with a median age of 8.7 [IQR, 4.4–16.0] years. DAP was used for a wide range of infections, including central line-associated bloodstream infections (CLABSIs; 32.5%), infective endocarditis (15.0%), surgical-site infections (12.5%), and osteomyelitis (12.5%). The most common pathogen isolated was MRSA (37.5%), and most patients were bacteremic (60.0%). The median DAP dose was 8 [IQR, 6–10] mg/kg, and the median duration of the DAP therapy was 11.5 [IQR, 4.8–18.8] days. Most patients achieved composite clinical success (75.0%). An adverse effect occurred in 5.0% of the patients. DAP was prescribed the most for its ease of use/ability to facilitate discharge (40.0%) and/or for issues with alternative therapies (37.5%). Conclusion: Most pediatric patients that received DAP demonstrated clinical success with a low incidence of adverse effects. Larger, real-world studies of DAP use are necessary to further assess clinical outcomes. [ABSTRACT FROM AUTHOR]

Abstract Background The increasing prevalence of methicillin-resistant Staphylococcus aureus (MRSA) strains resistant to non-beta-lactam antimicrobials poses a significant challenge in treating severe MRSA bloodstream infections. This study explores resistance development and mechanisms in MRSA isolates, especially after the first dalbavancin-resistant MRSA strain in our hospital in 2016. Methods This study investigated 55 MRSA bloodstream isolates (02/2015–02/2021) from the University Hospital of the Medical University of Vienna, Austria. The MICs of dalbavancin, linezolid, and daptomycin were assessed. Two isolates (16–33 and 19–362) resistant to dalbavancin were analyzed via whole-genome sequencing, with morphology evaluated using transmission electron microscopy (TEM). Results S.aureus BSI strain 19–362 had two novel missense mutations (p.I515M and p.A606D) in the pbp2 gene. Isolate 16–33 had a 534 bp deletion in the DHH domain of GdpP and a SNV in pbp2 (p.G146R). Both strains had mutations in the rpoB gene, but at different positions. TEM revealed significantly thicker cell walls in 16–33 (p

Abstract Background Antibiotic-containing carrier systems are one option that offers the advantage of releasing active ingredients over a longer period of time. In vitro sustained drug release from a carrier system consisting of microporous β-TCP ceramic and alginate has been reported in previous works. Alginate dialdehyde (ADA) gelatin gel showed both better mechanical properties when loaded into a β-TCP ceramic and higher biodegradability than pure alginate. Methods Dual release of daptomycin and BMP-2 was measured on days 1, 2, 3, 6, 9, 14, 21, and 28 by HPLC and ELISA. After release, the microbial efficacy of the daptomycin was verified and the biocompatibility of the composite was tested in cell culture. Results Daptomycin and the model compound FITC protein A (n = 30) were released from the composite over 28 days. A Daptomycin release above the minimum inhibitory concentration (MIC) by day 9 and a burst release of 71.7 ± 5.9% were observed in the loaded ceramics. Low concentrations of BMP-2 were released from the loaded ceramics over 28 days.

Vancomycin and daptomycin are frequently used in outpatient parenteral antimicrobial therapy (OPAT). We analyze health care utilization and cost to the health care system for vancomycin vs daptomycin in the outpatient setting and find that vancomycin results in significantly higher health care utilization and similar cost per course compared with daptomycin in OPAT. [ABSTRACT FROM AUTHOR]

Background: Daptomycin is a high‐use intravenous antimicrobial agent affording the convenience of once‐daily dosing. Prior studies suggest an opportunity to use a more operationally convenient fixed rather than weight‐based dosing but this approach has not been studied prospectively. Methods: This study quantified the probability of toxicity and efficacy end points by prospectively testing a fixed dose regimen of daptomycin (750 mg) in obese and non‐obese adults. At least, three daptomycin concentrations were measured at steady‐state for each patient. A population pharmacokinetic model was constructed to evaluate concentration‐time profiles and investigate covariates of daptomycin clearance. Simulations were performed to evaluate the probability of achieving efficacy (24‐h area under the curve (AUC0‐24) ≥ 666 mg∙h/L) and toxicity (minimum concentration (Cmin) ≥24.3 mg/L) targets for fixed (500–1000 mg) and weight‐based (6–12 mg/kg) daptomycin doses. Results: Thirty‐one patients (16 females, 15 males) with median (interquartile range (IQR)) age of 50 (30, 62) years and weight of 74 (54, 156) kg were included in the final analysis. Fixed dose daptomycin (750 mg) resulted in similar exposure across weights with a median (IQR) AUC0‐24 of 819 (499, 1501) mg∙h/L and 749 (606, 1265) mg∙h/L in patients weighing ≤74 kg and >74 kg, respectively. Overall, male sex and increased kidney function necessitate higher fixed and weight‐based doses to achieve efficacy. Creatine phosphokinase elevation was observed in two patients (6.5%) and predicted to be lower with fixed versus weight‐based regimens. Conclusions: Fixed daptomycin dosing adjusted for sex and kidney function is expected to improve the efficacy‐to‐toxicity ratio, transitions of care, and costs compared to weight‐based doses. However, no empiric dosing approach is predicted to achieve ≥90% efficacy while minimizing the risk of toxicity, so therapeutic drug monitoring should be considered on a patient‐specific basis. [ABSTRACT FROM AUTHOR]

Background and Objective: The dosage of daptomycin is usually based on body weight. However, it has been shown that this approach yields too high an exposure in obese patients. Pharmacokinetic and pharmacodynamic indexes (PK/PD) have been proposed for daptomycin's antibacterial effect (AUC/CMI >666) and toxicity (C0 > 24.3 mg/L). We previously developed machine learning (ML) algorithms to predict starting doses based on Monte Carlo simulations. We propose a new way to perform probability of target attainment based on an ML algorithm to predict the daptomycin starting dose. Methods: The Dvorchik model of daptomycin was implemented in the mrgsolve R package and 4950 pharmacokinetic profiles were simulated with doses ranging from 4 to 12 mg/kg. We trained and benchmarked four machine learning algorithms and selected the best to iteratively search for the optimal dose of daptomycin maximizing the event (AUC/CMI > 666 and C0 < 24.3 mg/L). The ML algorithm was evaluated in simulations and an external database of real patients in comparison with population pharmacokinetics. Results: The performance of the Xgboost algorithms developed to predict the event (ROC AUC) in the training and test set were 0.762 and 0.761, respectively. The most important prediction variables were dose, creatinine clearance, body weight and sex. In the external database of real patients, the starting dose administered based on the ML algorithm significantly improved the target attainment by 7.9% (p-value = 0.02929) in comparison with the dose administered based on body weight. Conclusion: The developed algorithm improved the target attainment for daptomycin in comparison with weight-based dosing. We built a Shiny app to calculate the optimal starting dose. [ABSTRACT FROM AUTHOR]

Vancomycin-resistant enterococci (VRE) commonly colonize the gut of individuals with hematologic malignancies or undergoing hematopoietic cell transplant (HCT) and may cause bacteremia. In 2012, we identified VRE isolates from patients and patients' rooms and showed transmission networks of highly genetically related daptomycin-resistant (DR)-VRE strains. This is a follow-up study performing whole-genome sequencing (WGS) and phylogenetic analyses on 82 clinical VRE strains isolated from stools and blood cultures of patients with leukemia and HCT between 2015 and 2019. Here, we observed transmission of highly genetically related strains between rooms on the same or on different floors, including a DR-VRE strain identified in 2012. Eleven of twenty-eight patients with DR-VRE were never exposed to daptomycin, suggesting horizontal transmission. Fifteen of the twenty-eight patients with DR-VRE died within 30 days of positive blood cultures. Amongst those, one DR-VRE strain belonging to ST1471 had the virulence gene bopD responsible for biofilm formation. Additionally, to our knowledge, this is the first report of a DR-VRE strain belonging to ST323 in the United States. In summary, our study demonstrated the emergence and persistence of VRE strains, especially DR-VRE, in our hospital. Adding WGS to routine infection control measures may timely identify potential horizontal VRE transmission including multi-drug-resistant isolates. [ABSTRACT FROM AUTHOR]

Daptomycin is an antibiotic with Gram‐positive activity, including methicillin‐resistant Staphylococcus aureus, for which optimal pediatric dosing is unknown. This study aimed to evaluate daptomycin exposures achieved with package label dosing and to identify dosing regimens necessary to enhance efficacy and minimize toxicity in children with S. aureus bacteremia. Monte Carlo simulations were performed to determine probability of target attainment (PTA) for six pediatric age cohorts. Area under the curve to minimum inhibitory concentration ratio (AUC0‐24:MIC) ≥666 was used to determine the PTA for efficacy (PTAE). Minimum concentration (Cmin) ≥24.3 mg/L determined the PTA for toxicity (PTAT). Acceptable dosing regimens were those which achieved the combined target of ≥90% PTAE and ≤5% PTAT. Package label dosing of daptomycin yielded insufficient efficacy with only 26.3% PTAE in children 13‐24 months, 39.5% PTAE in children 2‐6 years, 30.1% PTAE in children 7‐11 years, and 50.1% PTAE in adolescents ≥12 years. To achieve the combined efficacy and safety target, doses of 18‐24 mg/kg in children 3‐12 months, 20‐24 mg/kg in children 13‐24 months, 19‐24 mg/kg in children 2‐6 years, 17‐19 mg/kg in children 7‐11 years, and 10‐14 mg/kg in adolescents ≥12 years are necessary. Package label dosing resulted in suboptimal exposure for the majority of pediatric patients in all age groups evaluated. If targeting validated efficacy and safety endpoints, daily daptomycin doses of at least 20 mg/kg in children ≤6 years, 17 mg/kg in children 7‐11 years, and 10 mg/kg in adolescents ≥12 years are necessary. Clinical studies evaluating these higher doses are needed. [ABSTRACT FROM AUTHOR]

Background Daptomycin is widely used in critically ill patients for Gram-positive bacterial infections. Extracorporeal membrane oxygenation (ECMO) is increasingly used in this population and can potentially alter the pharmacokinetic (PK) behaviour of antibiotics. However, the effect of ECMO has not been evaluated in daptomycin. Our study aims to explore the effect of ECMO on daptomycin in critically ill patients through population pharmacokinetic (PopPK) analysis and to determine optimal dosage regimens based on both efficacy and safety considerations. Methods A prospective, open-label PK study was carried out in critically ill patients with or without ECMO. The total concentration of daptomycin was determined by UPLC-MS/MS. NONMEM was used for PopPK analysis and Monte Carlo simulations. Results Two hundred and ninety-three plasma samples were collected from 36 critically ill patients, 24 of whom received ECMO support. A two-compartment model with first-order elimination can best describe the PK of daptomycin. Creatinine clearance (CLCR) significantly affects the clearance of daptomycin while ECMO has no significant effect on the PK parameters. Monte Carlo simulations showed that, when the MICs for bacteria are  ≥1 mg/L, the currently recommended dosage regimen is insufficient for critically ill patients with CLCR > 30 mL/min. Our simulations suggest 10 mg/kg for patients with CLCR between 30 and 90 mL/min, and 12 mg/kg for patients with CLCR higher than 90 mL/min. Conclusions This is the first PopPK model of daptomycin in ECMO patients. Optimal dosage regimens considering efficacy, safety, and pathogens were provided for critical patients based on pharmacokinetic-pharmacodynamic analysis. [ABSTRACT FROM AUTHOR]

Daptomycin is a calcium-dependent cyclic lipopeptide antibiotic. It is one of only two new structural classes of antibiotics that have been approved for clinical use over the last 40 years. It is used to treat serious infections caused by Gram-positive bacteria. Although daptomycin has been used in the clinic since 2003, clinical resistance to daptomycin is not yet widespread. However, reports of clinical isolates that are resistant to daptomycin have been increasing in recent years, which is a cause for concern since daptomycin is often used to treat serious infections that are resistant to other antibiotics. Structural variation of antibiotics is a strategy that has often been used to overcome bacterial resistance. To pursue such a strategy with daptomycin, knowledge of its mechanism of action and methods for preparing daptomycin analogues, and the development of daptomycin structure–activity relationships (SARs) are necessary. This article, which is based on the 2023 Bernard Belleau Award Lecture, provides an overview of some of the key investigations that were undertaken by the Taylor group on daptomycin, including mechanism of action studies, the total synthesis of daptomycin, daptomycin SARs, and characterization of the interaction of daptomycin with phosphatidylglycerol, its primary target. [ABSTRACT FROM AUTHOR]

The stability of antibiotic preanalytical samples is a critical factor in therapeutic drug monitoring (TDM), a practice of undoubted importance for the proper therapeutic use of antibiotics, especially in complex management patients, such as pediatrics. This review aims to analyze the data in the literature regarding the preanalytical stability of some of the antibiotics for which TDM is most frequently requested. The literature regarding the preanalytical stability of amikacin, ampicillin, cefepime, ceftazidime, ciprofloxacin, daptomycin, gentamicin, levofloxacin, linezolid, meropenem, piperacillin, teicoplanin, and vancomycin in plasma, serum, whole blood, and dried blood/plasma spot samples was analyzed. Various storage temperatures (room temperature, 4 °C, −20 °C, and −80 °C) and various storage times (from 1 h up to 12 months) as well as subjecting to multiple freeze–thaw cycles were considered. The collected data showed that the non-beta-lactam antibiotics analyzed were generally stable under the normal storage conditions used in analytical laboratories. Beta-lactam antibiotics have more pronounced instability, particularly meropenem, piperacillin, cefepime, and ceftazidime. For this class of antibiotics, we suggest that storage at room temperature should be limited to a maximum of 4 h, storage at 2–8 °C should be limited to a maximum of 24 h, and storage at −20 °C should be limited to a maximum of 7 days; while, for longer storage, freezing at −80 °C is suggested. [ABSTRACT FROM AUTHOR]

More than 70% of bacteria are resistant to all or nearly all known antimicrobials, creating the need for the development of new types of antimicrobials or the use of "last-line" antimicrobial therapies for the treatment of multi-resistant bacteria. These antibiotics include Glycopeptide (Vancomycin), Polymyxin (Colistin), Lipopeptide (Daptomycin), and Carbapenem (Meropenem). However, due to the toxicity of these types of molecules, it is necessary to develop new rapid methodologies to be used in Therapeutic Drug Monitoring (TDM). TDM could improve patient outcomes and reduce healthcare costs by enabling a favorable clinical outcome. In this way, personalized antibiotic therapy emerges as a viable option, offering optimal dosing for each patient according to pharmacokinetic (PK) and pharmacodynamic (PD) parameters. Various techniques are used for this monitoring, including high-performance liquid chromatography (HPLC), gas chromatography-mass spectrometry (GC-MS), and immunoassays. The objective of this study is the development and characterization by ELISA of specific polyclonal antibodies for the recognition of the antibiotics Vancomycin (glycopeptide), Colistin (polymyxin), Daptomycin (lipopeptide), and Meropenem (carbapenem) for future applications in the monitoring of these antibiotics in different fluids, such as human plasma. The developed antibodies are capable of recognizing the antibiotic molecules with good detectability, showing an IC50 of 0.05 nM for Vancomycin, 7.56 nM for Colistin, 183.6 nM for Meropenem, and 13.82 nM for Daptomycin. These antibodies offer a promising tool for the precise and effective therapeutic monitoring of these critical antibiotics, potentially enhancing treatment efficacy and patient safety. [ABSTRACT FROM AUTHOR]

Background: Antibiotic-containing carrier systems are one option that offers the advantage of releasing active ingredients over a longer period of time. In vitro sustained drug release from a carrier system consisting of microporous β-TCP ceramic and alginate has been reported in previous works. Alginate dialdehyde (ADA) gelatin gel showed both better mechanical properties when loaded into a β-TCP ceramic and higher biodegradability than pure alginate. Methods: Dual release of daptomycin and BMP-2 was measured on days 1, 2, 3, 6, 9, 14, 21, and 28 by HPLC and ELISA. After release, the microbial efficacy of the daptomycin was verified and the biocompatibility of the composite was tested in cell culture. Results: Daptomycin and the model compound FITC protein A (n = 30) were released from the composite over 28 days. A Daptomycin release above the minimum inhibitory concentration (MIC) by day 9 and a burst release of 71.7 ± 5.9% were observed in the loaded ceramics. Low concentrations of BMP-2 were released from the loaded ceramics over 28 days. [ABSTRACT FROM AUTHOR]

BackgroundDaptomycin non-susceptible Staphylococcus aureus (DNS) strains pose a serious clinical threat, yet their characteristics remain poorly understood.MethodsDNS derivatives were generated by exposing S. aureus strains to subinhibitory concentrations of daptomycin. Competition experiment and growth kinetics experiment were used to observe the growth of bacteria. Galleria mellonella larvae and mouse skin abscess models were used to observe the virulence of bacteria. Transmission electron microscopy (TEM), cytochrome C experiment and biofilm formation experiment were used to observe the drug resistance phenotype. And homologous recombination was used to study the role of mutations.ResultsPhenotypic profiling of DNS strains revealed impaired growth, increased cell wall thickness, enhanced biofilm formation, reduced negative surface charge, and attenuated virulence compared to their wild-type strains. Whole genome sequencing identified mutations in mprF, cls2, and saeR in DNS strains. Allelic replacement experiments validated the roles of MprF L341F and Cls2 F60S substitutions in augmenting daptomycin non-susceptibility in Newman. Deletion of saeR in the NewmanMprFL341F strain and complementation of saeR in the Newman-DNS strain did not directly alter daptomycin susceptibility. However, the deletion of saeR was found to enhance competitive fitness under daptomycin pressure.ConclusionThis work validates adaptive laboratory evolution (ALE) for modeling clinical DNS strains and uncovers contributions of mprF, cls2, and saeR mutations to the adaptation and resistance mechanisms of S. aureus against daptomycin. These findings enrich our understanding of how S. aureus acquired resistance to daptomycin, thus paving the way for the development of more effective treatment strategies and offering potential molecular markers for resistance surveillance.

The Streptococcus mitis-oralis subgroup of the viridans group streptococci (VGS) are the most common cause of infective endocarditis (IE) in many parts of the world. These organisms are frequently resistant in vitro to standard β-lactams (e.g., penicillin; ceftriaxone [CRO]), and have the notable capacity for rapidly developing high-level and durable daptomycin resistance (DAP-R) during exposures in vitro, ex vivo, and in vivo. In this study, we used 2 prototypic DAP-susceptible (DAP-S) S. mitis-oralis strains (351; and SF100), which both evolved stable, high-level DAP-R in vitro within 1 to 3 days of DAP passage (5 to 20 μg/mL DAP). Of note, the combination of DAP + CRO prevented this rapid emergence of DAP-R in both strains during in vitro passage. The experimental rabbit IE model was then employed to quantify both the clearance of these strains from multiple target tissues, as well as the emergence of DAP-R in vivo under the following treatment conditions: (i) ascending DAP-alone dose-strategies encompassing human standard-dose and high-dose-regimens; and (ii) combinations of DAP + CRO on these same metrics. Ascending DAP-alone dose-regimens (4 to 18 mg/kg/d) were relatively ineffective at either reducing target organ bioburdens or preventing emergence of DAP-R in vivo. In contrast, the combination of DAP (4 or 8 mg/kg/d) + CRO was effective at clearing both strains from multiple target tissues (often with sterilization of bio-burdens in such organs), as well as preventing the emergence of DAP-R. In patients with serious S. mitis-oralis infections such as IE, especially caused by strains exhibiting intrinsic β-lactam resistance, initial therapy with combinations of DAP + CRO may be warranted.

ABSTRACTThe severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has posed enormous challenges to global public health. The use of antibiotics has greatly increased during the SARS-CoV-2 epidemic owing to the presence of bacterial co-infection and secondary bacterial infections. The antibiotics daptomycin (DAP) is widely used in the treatment of infectious diseases caused by gram-positive bacteria owing to its highly efficient antibacterial activity. It is pivotal to study the antibiotics usage options for patients of coronavirus infectious disease (COVID-19) with pneumonia those need admission to receive antibiotics treatment for bacterial co-infection in managing COVID-19 disease. Herein, we have revealed the interactions of DAP with the S protein of SARS-CoV-2 and the variant Omicron (B1.1.529) using the molecular docking approach and Omicron (B1.1.529) pseudovirus (PsV) mimic invasion. Molecular docking analysis shows that DAP has a certain degree of binding ability to the S protein of SARS-CoV-2 and several derived virus variants, and co-incubation of 1–100 μM DAP with cells promotes the entry of the PsV into human angiotensin-converting enzyme 2 (hACE2)-expressing HEK-293T cells (HEK-293T-hACE2), and this effect is related to the concentration of extracellular calcium ions (Ca2+). The PsV invasion rate in the HEK-293T-hACE2 cells concurrently with DAP incubation was 1.7 times of PsV infection alone. In general, our findings demonstrate that DAP promotes the infection of PsV into cells, which provides certain reference of antibiotics selection and usage optimization for clinicians to treat bacterial coinfection or secondary infection during SARS-CoV-2 infection.

Daptomycin is gaining prominence for the treatment of methicillin-resistant Staphylococcus aureus infections. However, the dosage selection for daptomycin in critically ill patients remains uncertain, especially in Chinese patients. This study aimed to establish the population pharmacokinetics of daptomycin in critically ill patients, optimize clinical administration plans, and recommend appropriate dosage for critically ill patients in China. The study included 64 critically ill patients. Blood samples were collected at the designated times. The blood daptomycin concentration was determined using validated liquid chromatography-tandem mass spectrometry. A nonlinear mixedeffects model was applied for the population pharmacokinetic analysis and Monte Carlo simulations of daptomycin. The results showed a twocompartment population pharmacokinetic model of daptomycin in critically ill adult Han Chinese patients. Monte Carlo simulations revealed that a daily dose of 400 mg of daptomycin was insufficient for the majority of critically ill adult patients to achieve the anti-infective target. For critically ill adult patients with normal renal function (creatinine clearance rate >90 mL/min), the probability of achieving the target only reached 90% when the daily dose was increased to 700 mg. For patients undergoing continuous renal replacement therapy (CRRT), 24 h administration of 500 mg met the pharmacodynamic goals and did not exceed the safety threshold in most patients. Therefore, considering its efficacy and safety, intravenous daptomycin doses are best scaled according to creatinine clearance, and an increased dose is recommended for critically ill patients with hyperrenalism. For patients receiving CRRT, medication is recommended at 24 h intervals. [ABSTRACT FROM AUTHOR]

Daptomycin use for gram-positive infections has increased. This cost minimization analysis aimed to determine cost and/or time savings of daptomycin over vancomycin. The estimated hospital cost savings was US$166.41 per patient, and pharmacist time saved of almost 20 minutes per patient. Daptomycin has the potential to save both time and money. [ABSTRACT FROM AUTHOR]

Daptomycin is a last‐line antibiotic commonly used to treat vancomycin‐resistant Enterococci, but resistance evolves rapidly and further restricts already limited treatment options. While genetic determinants associated with clinical daptomycin resistance (DAPR) have been described, information on factors affecting the speed of DAPR acquisition is limited. The multiple peptide resistance factor (MprF), a phosphatidylglycerol‐modifying enzyme involved in cationic antimicrobial resistance, is linked to DAPR in pathogens such as methicillin‐resistant Staphylococcus aureus. Since Enterococcus faecalis encodes two paralogs of mprF and clinical DAPR mutations do not map to mprF, we hypothesized that functional redundancy between the paralogs prevents mprF‐mediated resistance and masks other evolutionary pathways to DAPR. Here, we performed in vitro evolution to DAPR in mprF mutant background. We discovered that the absence of mprF results in slowed DAPR evolution and is associated with inactivating mutations in ftsH, resulting in the depletion of the chaperone repressor HrcA. We also report that ftsH is essential in the parental, but not in the ΔmprF, strain where FtsH depletion results in growth impairment in the parental strain, a phenotype associated with reduced extracellular acidification and reduced ability for metabolic reduction. This presents FtsH and HrcA as enticing targets for developing anti‐resistance strategies. [ABSTRACT FROM AUTHOR]

The purpose of the present study was to investigate the anti-staphylococcal activity of liposomal daptomycin against four biofilm-producing S. aureus and S. epidermidis clinical strains, three of which are methicillin-resistant. Neutral and negatively charged daptomycin-loaded liposomes were prepared using three methods, namely, thin-film hydration (TFH), a dehydration–rehydration vesicle (DRV) method, and microfluidic mixing (MM); moreover, they were characterized for drug encapsulation (EE%), size distribution, zeta-potential, vesicle stability, drug release, and drug integrity. Interestingly, whilst drug loading in THF and DRV nanosized (by extrusion) vesicles was around 30–35, very low loading (~4%) was possible in MM vesicles, requiring further explanatory investigations. Liposomal encapsulation protected daptomycin from degradation and preserved its bioactivity. Biofilm mass (crystal violet, CV), biofilm viability (MTT), and growth curve (GC) assays evaluated the antimicrobial activity of neutral and negatively charged daptomycin-liposomes towards planktonic bacteria and biofilms. Neutral liposomes exhibited dramatically enhanced inhibition of bacterial growth (compared to the free drug) for all species studied, while negatively charged liposomes were totally inactive. Biofilm prevention and treatment studies revealed high antibiofilm activity of liposomal daptomycin. Neutral liposomes were more active for prevention and negative charge ones for treating established biofilms. Planktonic bacteria as well as the matured biofilms of low daptomycin-susceptible, methicillin-resistant Staphylococcus aureus (MRSA) and Staphylococcus epidermidis (MRSE) strains were almost completely eradicated by liposomal-daptomycin, indicating the need for their further exploration as antimicrobial therapeutics. [ABSTRACT FROM AUTHOR]

Introduction: Acute eosinophilic pneumonia (AEP) is a rare respiratory condition caused by eosinophil accumulation in the pulmonary tissue that can be related to drug administration. Daptomycin, an antibiotic active against gram-positive bacteria, is one of the leading causes of AEP among drugs. In order to raise awareness of this rare syndrome, in our work we have described a case of an 82-year-old male with Enterococcus faecalis endocarditis treated with daptomycin, who developed a daptomycin-induced AEP. We have performed a systematic review of the literature for all similar reported cases. Methods: The systematic review was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. To conduct the analysis, the terms "daptomycin AND eosinoph* AND pneum*" were entered into the databases Medline, CINAHL, and Embase on April 13, 2023. We considered all relevant records documenting AEP after daptomycin use. No restrictions in terms of year or language were made. A formal appraisal of observational studies was performed by Newcastle-Ottawa Scale. All results and data were reported by means of tables. Results: Our search identified 93 relevant records, published between 2007 and 2023. A total of 120 patients were considered. Patients who experienced AEP were mostly males (n = 88, 73.3%) with a mean age of 68.28 years (SD 11.54). Daptomycin was most frequently prescribed for osteoarticular infections (n = 75, 62.5%) and to treat gram-positive cocci infections. The most frequently isolated pathogen was methicillin-resistant Staphylococcus aureus. Daptomycin was mostly used with off-label indications (n = 89, 74%). Symptoms of AEP were usually reported after a mean of 21.75 days of treatment (range 3–84) and typically included fever, dyspnea, dry cough, and acute respiratory failure. Reported treatment strategies invariably included daptomycin withdrawal, respiratory support, and corticosteroid treatment. One hundred and sixteen patients fully recovered. A fatal outcome was described in 4 patients. Suggestive symptoms and imaging raised suspicion for AEP, confirmed with bronchoalveolar lavage in 57.5% of the cases. Discussion and Conclusions: Daptomycin-induced AEP is a rare but potentially fatal complication, mostly reported after long treatment with daptomycin. Clinicians should be aware of this syndrome, as it could be initially misdiagnosed for an acute infectious respiratory syndrome, resulting in a delay in its diagnosis and treatment. Furthermore, since the risk of developing AEP is increased by longer drug exposure, caution should be used when discussing the use of daptomycin in longer treatment regimens. [ABSTRACT FROM AUTHOR]

Background The indications of daptomycin have been extended to off-label indications including prosthesis-related infection, and bone and joint infection (BJI). However, efficacy and safety have not been thoroughly demonstrated compared with the standard of care. This systematic review and meta-analysis aimed to compare the treatment effect of daptomycin and glycopeptides for complicated infections. Materials and methods MEDLINE, Embase and Web of Science were searched for randomized controlled trials (RCTs) comparing daptomycin and standard of care for Gram-positive infections, published until 30 June 2021. The primary outcome was defined as all-cause mortality. Secondary outcomes were clinical and microbiological success. The main safety outcome was any severe adverse event (SAE) (grade  ≥3). Results Overall, eight RCTs were included in the meta-analysis, totalling 1095 patients. Six (75%) were in complicated skin and soft-structure infections, one (12.5%) in bacteraemia and one (12.5%) in a BJI setting. Six RCTs used vancomycin as a comparator and two used either vancomycin or teicoplanin. All-cause mortality and clinical cure were not different between groups. The microbiological cure rate was superior in patients who received daptomycin [risk ratio (RR) = 1.17 (95% CI: 1.01–1.35)]. The risk of SAEs [RR = 0.57 (95% CI: 0.36–0.90)] was lower in the daptomycin arm. Conclusions While daptomycin is associated with a significantly lower risk of SAEs and a better microbiological eradication, substantial uncertainty remains about the best treatment strategy in the absence of good-quality evidence, especially in bacteraemia and endocarditis where further RCTs should be conducted. [ABSTRACT FROM AUTHOR]

Methicillin-resistant Staphylococcus aureus (MRSA) strains pose a significant threat as common causes of bacterial infections in hospitals, often resistant to available antibiotics such as daptomycin, vancomycin, and linezolid. The continuous emergence of new MRSA isolates with no effective treatment options underscores a real threat to health among humans and animals, and the number of effective antibiotic therapies decreases with each passing year. In this review, we provide an overview of the most common genetic mechanisms of resistance to a broad spectrum of antibiotics in methicillin-resistant S. aureus. [ABSTRACT FROM AUTHOR]

Background: The preferred antibiotic salvage regimen for persistent methicillin-susceptible Staphylococcus aureus bacteremia (MSSAB) is unclear. Ertapenem with cefazolin or an antistaphylococcal penicillin has been primarily described, but identifying alternative carbapenem-sparing options may support antibiotic stewardship efforts and decrease the risk of antibiotic-associated Clostridioides difficile infection. Objective: We sought to evaluate the effectiveness and safety of daptomycin plus oxacillin (D/O) for persistent MSSAB. Methods: This was a single-center, retrospective cohort of patients with persistent MSSAB who received D/O between January 1, 2014, and January 1, 2023. Adult patients were included if they had blood cultures positive for MSSA ≥72 hours and received D/O combination for ≥48 hours. Patients were excluded if they were pregnant, incarcerated, or received another antibiotic considered to have excellent activity against MSSA. The primary outcome was time to MSSA bacteremia clearance post-daptomycin initiation. Secondary outcomes included microbiological cure, hospital length of stay, 90-day all-cause mortality, MSSA bacteremia-related mortality, 90-day readmission for MSSAB, and incidence of antibiotic-associated adverse effects. Time to MSSAB clearance post-D/O initiation was plotted using Kaplan-Meier estimation. Results: Seven unique patient encounters were identified including 4 with endocarditis. Despite a median MSSA bacteremia duration of 7.8 days, median clearance was 2 days post-daptomycin initiation. All achieved microbiological cure, and no adverse effects were reported. Ninety-day all-cause mortality, MSSAB-related mortality, and 90-day readmission for MSSAB occurred in 28.6%, 14.3%, and 14.3% of patients, respectively. Conclusions and Relevance: D/O was an effective, well-tolerated salvage regimen in this cohort and may represent a carbapenem-sparing option for persistent MSSAB. [ABSTRACT FROM AUTHOR]

Daptomycin-induced eosinophilic pneumonia (DIEP) is a rare complication of daptomycin use. Manifestations most commonly include fever, hypoxia, dyspnea, cough, eosinophilia, and lung changes on radiographs and CT. Patients typically have had recent daptomycin exposure and develop fever, dyspnea, infiltrates on chest radiograph, more than 25% eosinophils on bronchoalveolar lavage, and improvement of symptoms after withdrawal of daptomycin. Treatment includes discontinuation of daptomycin, corticosteroids, and supportive measures such as supplemental oxygen. Clinicians should have a high index of suspicion for DIEP in patients who develop new onset of pulmonary and systemic signs and symptoms after initiation of daptomycin. [ABSTRACT FROM AUTHOR]

Infections caused by Staphylococcus aureus, notably methicillin‐resistant S. aureus (MRSA), pose treatment challenges due to its ability to tolerate antibiotics and develop antibiotic resistance. The former, a mechanism independent of genetic changes, allows bacteria to withstand antibiotics by altering metabolic processes. Here, a potent methylazanediyl bisacetamide derivative, MB6, is described, which selectively targets MRSA membranes over mammalian membranes without observable resistance development. Although MB6 is effective against growing MRSA cells, its antimicrobial activity against MRSA persisters is limited. Nevertheless, MB6 significantly potentiates the bactericidal activity of gentamicin against MRSA persisters by facilitating gentamicin uptake. In addition, MB6 in combination with daptomycin exhibits enhanced anti‐persister activity through mutual reinforcement of their membrane‐disrupting activities. Crucially, the "triple" combination of MB6, gentamicin, and daptomycin exhibits a marked enhancement in the killing of MRSA persisters compared to individual components or any double combinations. These findings underscore the potential of MB6 to function as a potent and selective membrane‐active antimicrobial adjuvant to enhance the efficacy of existing antibiotics against persister cells. The molecular mechanisms of MB6 elucidated in this study provide valuable insights for designing anti‐persister adjuvants and for developing new antimicrobial combination strategies to overcome the current limitations of antibiotic treatments. [ABSTRACT FROM AUTHOR]

The objective was to evaluate the incidence of nephrotoxicity related to vancomycin and other anti-MRSA antibiotics (linezolid and daptomycin). Patients receiving any of these drugs between July 2014 and December 2020 at a tertiary hospital were included. Renal failure was evaluated using the acute renal injury (AKIN) system. Univariate analysis was conducted on the 5806 patients who were included. Among them, 1023 patients (17.62%) developed renal failure. The renal damage incidence was 14.74% (496/3365) for vancomycin, 19.13% (367/1918) for linezolid, and 30.59% (160/523) for daptomycin. Patients with lower basal glomerular filtration had a higher risk of AKIN. In the vancomycin group, the risk factors were high creatinine and urea serum basal values, duration of treatment (DOT), body mass index (BMI), ICU stay, age, and low CKDEPI and albumin levels. In the linezolid group, AKIN was linked to high creatinine and urea levels, BMI, age, and ICU stay and to low CKDEPI levels; for daptomycin, AKIN was associated with low CKDEPI and albumin levels and a long DOT. Patients with AKIN showed higher mortality rates. Vancomycin-associated nephrotoxicity remains a great concern. However, linezolid and daptomycin could also cause nephrotoxicity. Bearing in mind risk factors that may prompt nephrotoxicity in hospitalized patients taking anti-staphylococcal antibiotics will result in better pharmacotherapeutic management. [ABSTRACT FROM AUTHOR]

Introduction: Weekly intravenous (IV) oritavancin and daily daptomycin were compared in an outpatient setting following extensive surgical debridement for treating patients with osteomyelitis. Methods: This was a retrospective, observational study of patients diagnosed with acute osteomyelitis. Exclusion criteria were the use of Gram-negative antibiotic therapy, use of antibiotics for more than 48 h prior to oritavancin or daptomycin or prior use of > 2 doses of oritavancin or more than 4 weeks of daptomycin. Clinical success was resolution or improvement of symptoms and no further treatment. Data were analyzed with Chi-square test or Fisher's exact test. Results: Consecutive outpatients (n = 150) with acute osteomyelitis who were treated with oritavancin or daptomycin (1:1) following extensive surgical debridement were identified. Staphylococcusaureus was the most common pathogen (n = 117). No patient in either group received prior antibiotic therapy (previous 30 days) or was hospitalized within 90 days prior to surgical debridement. Twenty-one (28%) patients prescribed oritavancin had chronic kidney disease, seven of whom were receiving hemodialysis or peritoneal dialysis. Compared to oritavancin, patients prescribed daptomycin had higher rates of all-cause readmission [odds ratio (OR) 2.89; p < 0.001], more infection-related readmission (OR 3.19; p < 0.001), and greater likelihood of receiving antibiotics post-discontinuation of initial therapy (OR 2.13; p < 0.001). Repeat surgical debridement was required for 68.0% with daptomycin vs. 23.1% with oritavancin (p < 0.001). Conclusions: Oritavancin demonstrated a significantly higher rate of clinical success compared to daptomycin, with lower all-cause and infection-related readmissions, reduced need for repeat surgical debridement, and fewer additional antibiotic requirements. [ABSTRACT FROM AUTHOR]

During the last two decades, the incidence of late-onset sepsis (LOS) has increased due to improved survival of premature neonates. Persistent bacteremia (PB) in LOS is defined as more than two positive blood cultures obtained on different calendar days during the same infectious episode. Although rare, PB should be treated aggressively to prevent adverse outcomes. Daptomycin, a lipopeptide antibiotic, has been used in neonates with persistent coagulase-negative staphylococci (CoNS) bacteremia with promising results, but studies reporting on the efficacy and safety of the agent are scarce. The purpose of this study was to evaluate the efficacy and safety of daptomycin use for persistent CoNS bacteremia in a neonatal cohort. This is a retrospective, observational, single-center study of neonates treated with daptomycin during 2011–2022 in the Tertiary Neonatal Intensive Care Unit (NICU) of the University General Hospital of Patras, Greece. For the years 2011–2022, there were 3.413 admissions to the NICU. During the last 3 years (2020–2022)—the active epidemiological surveillance period—123 infants (out of 851 admissions, 14.4%) developed CoNS bacteremia (LOS). During the study period, twelve infants with PB were treated with daptomycin. They had a median gestational age of 32 weeks (IQR 31–34) and mean (SD) birth weight of 1.840 (867) grams. CoNS bacteremia isolates were s. epidermidis (50%), s. haemolyticus (20%), s. hominis (20%) and s. warneri (10%). The decision to start daptomycin (6 mg/kg/dose twice daily) was taken on median day 10 (ΙQR 7–15) of infection. None of the infants had focal complications or meningitis. Daptomycin therapy caused no renal, hepatic, muscular or gastrointestinal adverse events. One neonate developed seizures, and one death occurred due to multiple complications of prematurity. Most infants (11/12) were successfully treated and eventually had negative blood culture. Daptomycin monotherapy showed an adequate cure rate in premature neonates with persistent CoNS bacteremia in a tertiary NICU. In our study, daptomycin was effective and well tolerated; the safety profile, however, needs to be confirmed in larger studies and randomized controlled trials. [ABSTRACT FROM AUTHOR]

Introduction: The rapid emergence and global spread of COVID-19 have underscored the critical need for understanding patient characteristics, clinical outcomes, and the microbiological landscape within intensive care settings. The study aims to identify the most common microbes causing pulmonary coinfections in COVID-19 ICU patients and to determine the optimal empirical antimicrobial treatment for this patient population. Material and methods: In the following single-center retrospective cohort study, we collected medical data on 201 patients admitted to the ICU due to COVID-19. Further, we Identified the primary causative pathogens of pulmonary coinfection. The study outcomes were death or ICU discharge. Results: The study analyzed 201 COVID-19 patients in the ICU, revealing a balanced distribution between those with (52%) and without (48%) pulmonary infections. In our cohort, the mean BMI was 33.0. The subgroup with pulmonary coinfections did not show statistically significant differences in the prevalence of diabetes and hypertension compared to those without such coinfections. Patients with pulmonary infections exhibited more severe respiratory compromise, necessitating increased mechanical ventilation and extended ICU stays. Pathogen isolation highlighted Staphylococcus aureus, Enterobacter cloacae, and Enterococcus faecalis as predominant, with a notable shift towards resistant strains like Klebsiella pneumoniae ESBL and Acinetobacterbaumannii MDR post-48 hours of admission. Antibiotic susceptibility testing underscored the effectiveness of specific agents against MSSA, while revealing variable resistance patterns among Enterobacter cloacae and Enterococcus faecalis, particularly against Daptomycin and Levofloxacin. The most commonly used antibiotics were ceftriaxone and levofloxacin. Conclusions: The number of used antibiotics, including broad-spectrum, increased the occurrence of multi-drug resistant bacteria. [ABSTRACT FROM AUTHOR]

Daptomycin is one of the last therapeutic resources for multidrug-resistant gram-positive bacteria. Despite its structural similarities with glycopeptides, its mechanisms of action and resistance are different and in some respects are not completely understood. Mutations in several genes have been associated with daptomycin resistance, especially in mprF, walkR, rpoB and rpoC, but their role and importance remain to be elucidated. We have studied mutations in 11 genes, which have been previously associated with daptomycin non-susceptibility, in nine daptomycin-non-susceptible Staphylococcus aureus clinical isolates (daptomycin MIC: >1 mg/L). Susceptibility to daptomycin, vancomycin, linezolid, oxacillin, telavancin and dalbavancin was studied. walkR, agrA, cls1, cls2, fakA, pnpA, clpP, prs, rpoB, rpoC and mprF were amplified by PCR and sequenced. The sequences were compared with the S. aureus ATCC 25923 complete genome (GenBank gi: 685631213) by using BLAST® software. We did not find any changes in walkR, pnpA, prs and clpP. All isolates excepting isolate MSa5 showed a high number of significant mutations (between 13 and 25 amino acid changes) in mprF. Most isolates also showed mutations in the rpo genes, the cls genes and fakA. Daptomycin non-susceptibility in S. aureus clinical isolates seems to be reached through different mutation combinations when compared to S. aureus ATCC 25293. Especially mprF and cls1 showed very high polymorphism in most isolates. Meanwhile, one isolate, MSa5, showed only single mutation in mprF (P314T). [ABSTRACT FROM AUTHOR]