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Comparison of daptomycin MIC results by DIN, NCCLS, SFM, and SRGA methods for 297 Gram-positive organisms.

Daptomycin is a novel lipopeptide antibiotic with potent in vitro antibacterial activity against Gram-positive pathogens. For daptomycin minimal inhibitory concentration (MIC) testing, National Committee for Clinical Laboratory Standards (NCCLS) recommends the use of broth containing physiological levels of calcium (50 microg/ml). The daptomycin susceptibility of 297 organisms was determined by NCCLS (Mueller-Hinton (MH) broth), Deutsches Institut für Normung (DIN; isotonic broth), Société Française de Microbiologie (SFM; three batches MH agar), and Swedish Reference Group for Antibiotics (SRGA; PDM agar). All media were supplemented to 50 microg/ml Ca(2+). There was good correlation between DIN and SFM methods (for staphylococci) with NCCLS results. Enterococci MICs using SFM methods were one to three dilutions lower and pneumococci results were one dilution higher than NCCLS. SRGA results were higher than NCCLS by one to four dilutions. Use of isotonic agar is an accepted alternative to isosensitest agar for the DIN method.

Anti-Bacterial Agents↗

Activity of daptomycin against multi-resistant Gram-positive bacteria including enterococci and Staphylococcus aureus resistant to linezolid.

The activity of daptomycin was assessed against 545 isolates of Gram-positive bacteria including enterococci, coagulase-positive and -negative staphylococci, beta-haemolytic streptococci, viridans streptococci and coryneforms. The panel of isolates was biased towards those with resistance to first-line antimicrobial agents and included linezolid-resistant enterococci and Staphylococcus aureus. MICs of daptomycin were < or =1mg/l for all the staphylococci, streptococci, and coryneforms, except for two isolates of Corynebacterium aquaticum, for which MICs were 8 mg/l. Daptomycin MICs were < or =2 and < or =4 mg/l for Enterococcus faecalis and Enterococcus faecium, respectively.

Acetamides↗

In vitro activity of daptomycin against clinical isolates with reduced susceptibilities to linezolid and quinupristin/dalfopristin.

An initiative was taken to determine the in vitro activity of daptomycin against 85 Gram-positive isolates with reduced susceptibilities to linezolid and quinupristin/dalfopristin. Daptomycin had potent activity against all strains, with a Staphylococcus spp. minimum inhibitory concentration (MIC) < or =2 microg/mL and an Enterococcus spp. MIC < or =8 microg/mL. Resistance to linezolid and quinupristin/dalfopristin appears to be independent of reduced susceptibility to daptomycin.

Acetamides↗

Bactericidal activity of daptomycin, vancomycin, teicoplanin and linezolid against Staphylococcus aureus, Enterococcus faecalis and Enterococcus faecium using human peak free serum drug concentrations.

The bactericidal activities of daptomycin, vancomycin, teicoplanin and linezolid at human peak free serum concentrations (C(max,free)) were determined against Staphylococcus aureus (one methicillin-susceptible and two methicillin-resistant strains), Enterococcus faecalis and Enterococcus faecium (one vancomycin-susceptible and one vancomycin-resistant strain of each). Daptomycin was rapidly bactericidal against 7/7 strains at C(max,free) of 22.0 mg/L (corresponding to 63% protein binding) and against 3/7 strains at 4.8 mg/L (corresponding to 92% protein binding). Vancomycin (18.0 mg/L) was bactericidal against only two strains. Both teicoplanin (4.5 mg/L) and linezolid (10.4 mg/L) were consistently bacteriostatic. Daptomycin is a useful option for the treatment of Gram-positive infections owing to its strong bactericidal activity.

Acetamides↗

Chemoenzymatic design of acidic lipopeptide hybrids: new insights into the structure-activity relationship of daptomycin and A54145.

The acidic lipopeptides, including the clinically approved antibiotic daptomycin, constitute a class of structurally related branched cyclic peptidolactones and peptidolactams synthesized by nonribosomal peptide synthetases (NRPSs). In this study, the excised peptide cyclases from A54145 and daptomycin NRPSs were shown to be able to catalyze the macrocyclization of peptide thioester substrates, which were chemically produced by solid phase peptide synthesis. Applying this chemoenzymatic strategy, we generated derivatives of A54145 and daptomycin as well as hybrid molecules of both compounds. Bioactivity determination of the derived cyclic molecules revealed new insights into the structure-activity relationship of the acidic lipopeptide family. The general importance of several amino acid positions, including two conserved aspartic acid residues, was confirmed to be substantial for antibiotic potency. As a robust macrocyclization catalyst, the peptide cyclase excised from A54145 synthetase is the first cyclase of a branched cyclic lipopeptide, which catalyzes both macrolactonization and macrolactamization. The results presented herein illustrate the advantages of combining organic synthesis with natural product biosynthetic enzymes to explore the interplay between structural features and biological activity.

Amino Acid Sequence↗

Rhabdomyolysis during therapy with daptomycin.

The use of daptomycin has been associated with an elevation in creatine phosphokinase level, with a reported incidence of 2.8% in phase III clinical trials. Published case reports have documented the presence of myopathy in patients who received daptomycin; however, there have been no previously reported cases of rhabdomyolysis in animals or humans to date. We describe a case of rhabdomyolysis during therapy with daptomycin.

Anti-Bacterial Agents↗

Bactericidal activity of daptomycin against Streptococcus pneumoniae compared with eight other antimicrobials.

A spectrum of pneumococci with varying susceptibilities to beta-lactams, macrolides and quinolones was tested for susceptibility to nine antibiotics, including the novel lipopeptide daptomycin. Daptomycin was active against all strains (MIC range </=0.5 mg/L; MIC(50) 0.125 mg/L; MIC(90) 0.25 mg/L). All pneumococci were susceptible to vancomycin, teicoplanin, linezolid and quinupristin/dalfopristin, with MICs < 4.0 mg/L. Time-kill assays with eight strains demonstrated that daptomycin (2 x MIC) was bactericidal in seven of eight strains tested at 24 h, with >90% killing at 1 h.

4-Quinolones↗

Daptomycin: a lipopeptide antibiotic for the treatment of serious Gram-positive infections.

Infections caused by drug-resistant pathogens are on the rise. Daptomycin, a cyclic lipopeptide with activity against most Gram-positive pathogens, including vancomycin-resistant enterococci and methicillin-resistant Staphylococcus aureus, is a newly US-FDA approved antimicrobial for complicated skin and skin structure infections (cSSSI). Daptomycin has a unique mechanism of action that results in destruction of the membrane potential. The rapid bactericidal activity of daptomycin makes it an attractive antibiotic for serious Gram-positive infections.

Anti-Bacterial Agents↗

Daptomycin biosynthesis in Streptomyces roseosporus: cloning and analysis of the gene cluster and revision of peptide stereochemistry.

Daptomycin is a 13 amino acid, cyclic lipopeptide produced by a non-ribosomal peptide synthetase (NRPS) mechanism in Streptomyces roseosporus. A 128 kb region of S. roseosporus DNA was cloned and verified by heterologous expression in Streptomyces lividans to contain the daptomycin biosynthetic gene cluster (dpt). The cloned region was completely sequenced and three genes (dptA, dptBC, dptD) encoding the three subunits of an NRPS were identified. The catalytic domains in the subunits, predicted to couple five, six or two amino acids, respectively, included a novel activation domain and amino-acid-binding pocket for incorporating the unusual amino acid l-kynurenine (Kyn), three types of condensation domains and an extra epimerase domain (E-domain) in the second module. Novel genes (dptE, dptF) whose products likely work in conjunction with a unique condensation domain to acylate the first amino acid, as well as other genes (dptI, dptJ) probably involved in supply of the non-proteinogenic amino acids l-3-methylglutamic acid and Kyn, were located next to the NRPS genes. The unexpected E-domain suggested that daptomycin would have d-Asn, rather than l-Asn, as originally assigned, and this was confirmed by comparing stereospecific synthetic peptides and the natural product both chemically and microbiologically.

Amino Acid Motifs↗

Daptomycin susceptibility of unusual gram-positive bacteria: comparison of results obtained by the Etest and the broth microdilution method.

MICs of daptomycin, linezolid, and vancomycin against 212 isolates, including Listeria monocytogenes and Pediococcus, Leuconostoc, Rhodococcus, and Nocardia spp., were determined by the broth microdilution method; daptomycin MICs were also determined by the Etest. Except with those for Leuconostoc spp., daptomycin Etest MICs showed >90% agreement with MICs obtained by the broth microdilution method.

Culture Media↗

Activities of daptomycin and teicoplanin against Staphylococcus haemolyticus and Staphylococcus epidermidis, including evaluation of susceptibility testing recommendations.

The in vitro activities of daptomycin, teicoplanin, and three other antimicrobial agents were determined against 105 strains of Staphylococcus haemolyticus and 92 strains of Staphylococcus epidermidis. The MICs for 90% of strains tested (MIC90s) of fusidic acid and rifampin were less than or equal to 0.25 microgram/ml. The MIC90s of daptomycin and vancomycin were less than or equal to 4 micrograms/ml. Teicoplanin had a comparable MIC90 of less than or equal to 4 micrograms/ml for isolates of S. epidermidis. However, MIC90s were 8 and 16 micrograms/ml for oxacillin-susceptible and oxacillin-resistant S. haemolyticus, respectively. Disk diffusion tests were evaluated for daptomycin and teicoplanin. Disks with 30 micrograms of teicoplanin performed satisfactorily when S. epidermidis was tested, but when S. haemolyticus was tested, there was a very major error rate of 10% and a minor error rate of 38%.

Anti-Bacterial Agents↗

Daptomycin disrupts membrane potential in growing Staphylococcus aureus.

Daptomycin (LY146032) caused a calcium-dependent dissipation of the membrane potential (delta psi) in Staphylococcus aureus without noticeably affecting the chemical gradient (delta pH) across the membrane. The effect of daptomycin on membrane energization may account for many of the inhibitory effects on macromolecular biosyntheses and membrane function reported for this antibiotic. Our evidence indicates that the bactericidal activity of daptomycin is dependent on an available delta psi.

Anti-Bacterial Agents↗

Comparative in vitro activities of teicoplanin, daptomycin, ramoplanin, vancomycin, and PD127,391 against blood isolates of gram-positive cocci.

The in vitro activities of teicoplanin, daptomycin, ramoplanin, and PD127,391, a new quinolone, were compared with that of vancomycin. Teicoplanin showed the lowest MICs against Enterococcus faecalis. Ramoplanin was slightly more active than the other peptide antibiotics against oxacillin-resistant Staphylococcus aureus. The MICs of the four peptide antibiotics were similar for the oxacillin-susceptible S. aureus. Daptomycin had good activity against staphylococci but was the least active agent against E. faecalis. The MICs of vancomycin against all isolates were in general higher than those of the new antibiotics, with the exceptions of the MICs of daptomycin against E. faecalis and teicoplanin against oxacillin-resistant Staphylococcus epidermidis. PD127,391 was the most active agent against all staphylococcal isolates.

Anti-Bacterial Agents↗

Activity of daptomycin against recent North American isolates of Streptococcus pneumoniae.

Daptomycin MICs at which 50% of isolates were inhibited (MIC(50)s) and MIC(90)s determined by the NCCLS broth microdilution method were both 0.25 microg/ml (range, 0.06 to 2 microg/ml) for 350 pneumococcal isolates. MICs determined by E test strips on commercially prepared Mueller-Hinton sheep blood agars with different calcium contents were 2 to 3 dilutions higher than those determined by strips that contained daptomycin plus calcium. Daptomycin zone diameters varied little on the same media.

Anti-Bacterial Agents↗

Impact of Enterococcus faecalis on the bactericidal activities of arbekacin, daptomycin, linezolid, and tigecycline against methicillin-resistant Staphylococcus aureus in a mixed-pathogen pharmacodynamic model.

We inoculated an in vitro pharmacodynamic model simultaneously with clinical isolates of methicillin-resistant Staphylococcus aureus and an enterocin-producing enterococcus (vancomycin-resistant Enterococcus faecalis, ampicillin susceptible) at 7 log10 CFU/ml to examine enterocin effects and antimicrobial activity on staphylococci. The investigated antimicrobial regimens were 100 mg arbekacin every 12 h (q12h), 6 mg daptomycin per kg of body weight/day, 600 mg linezolid q12h, and 100 mg tigecycline q24h alone and in combination (daptomycin, linezolid, and tigecycline) with arbekacin. Simulations were performed in triplicate; bacterial quantification occurred over 48 h, and development of resistance was evaluated throughout. When we evaluated the impact of antimicrobial activity against S. aureus alone, daptomycin demonstrated bactericidal activity (>or=3 log10 CFU/ml kill), whereas arbekacin, linezolid, and tigecycline displayed bacteriostatic activities (<3 log10 CFU/ml kill). In the mixed-pathogen model, early and distinctive stunting of S. aureus growth was noted (1.5 log CFU/ml difference) in the presence of enterocin-producing E. faecalis compared to growth controls run individually (P=0.02). Most noteworthy was that in the presence of enterocin-producing E. faecalis, bactericidal activity was observed with arbekacin and tigecycline and with the addition of arbekacin to linezolid. Antagonism was noted for the combination of tigecycline and arbekacin against S. aureus in the presence of enterocin-producing E. faecalis. Our research demonstrates that the inhibitory effect of E. faecalis contributed significantly to its overall antimicrobial impact on S. aureus. This contribution was enhanced or improved compared to the activity of each antimicrobial alone. Further research is warranted to determine the impact of polymicrobial infections on antimicrobial activity.

Acetamides↗

Induction of daptomycin heterogeneous susceptibility in Staphylococcus aureus by exposure to vancomycin.

We studied vancomycin and daptomycin susceptibility in methicillin-resistant Staphylococcus aureus from patients exposed to vancomycin, glycopeptide-intermediate S. aureus, and S. aureus passaged in vancomycin-containing medium. A correlation between vancomycin and daptomycin heteroresistance was noted in some strains, suggesting that exposure of S. aureus to vancomycin may affect susceptibility to daptomycin.

Anti-Bacterial Agents↗

Development of Daptomycin resistance in vivo in methicillin-resistant Staphylococcus aureus.

Daptomycin is a new lipopeptide antibiotic that is rapidly bactericidal against Staphylococcus aureus. We report daptomycin resistance and treatment failure in 2 patients with osteomyelitis due to methicillin-resistant S. aureus. Disk diffusion susceptibility testing failed to detect resistance. Daptomycin at high concentration retained bactericidal activity against resistant isolates.

Aged↗

Clinical progression of methicillin-resistant Staphylococcus aureus vertebral osteomyelitis associated with reduced susceptibility to daptomycin.

Daptomycin, a novel cyclic lipopeptide antibiotic, exhibits rapid bactericidal activity in vitro against most clinically relevant gram-positive organisms, including drug-resistant pathogens. Herein we describe a patient in whom methicillin-resistant Staphylococcus aureus with reduced susceptibility to daptomycin was responsible for bacteremia and progressive vertebral osteomyelitis during daptomycin therapy.

Anti-Bacterial Agents↗