scholarly journals Ability of Bicarbonate Supplementation to Sensitize Selected Methicillin-Resistant Staphylococcus aureus (MRSA) Strains to β-Lactam Antibiotics in an Ex Vivo Simulated Endocardial Vegetation Model

2019 ◽  
Author(s):  
Warren E. Rose ◽  
Ana M. Bienvenida ◽  
Yan Q. Xiong ◽  
Henry F. Chambers ◽  
Arnold S. Bayer ◽  
...  
Keyword(s):  
Bactericidal Activity ◽  
Ex Vivo ◽  
Rabbit Model ◽  
Growth Media ◽  
Highly Active ◽  
Mueller Hinton ◽  
Mrsa Strains ◽  
High Level ◽  
Susceptibility Breakpoint

ABSTRACTSupplementation of standard growth media (cation-adjusted Mueller-Hinton Broth [CAMHB]) with bicarbonate (NaHCO3) significantly increases β-lactam susceptibility of selected MRSA strains (“NaHCO3-responsive”). This “sensitization” phenomenon translated to enhanced β-lactam efficacy in a rabbit model of endocarditis. The present study evaluated NaHCO3-mediated β-lactam MRSA sensitization using an ex vivo pharmacodynamic model, featuring simulated endocardial vegetations (SEVs), to more closely mimic the host microenvironment. Four previously described MRSA strains were used: two each exhibiting in vitro “NaHCO3-responsive” or “NaHCO3-nonresponsive” phenotypes. Cefazolin (CFZ) and oxacillin (OXA) were evaluated in CAMHB±NaHCO3. Intra-SEV MRSA killing was determined over 72 hr exposure. In both NaHCO3-responsive strains, supplementation with 25 mM or 44 mM NaHCO3 significantly reduced β-lactam MICs to below the OXA susceptibility breakpoint (≤ 4 mg/L) resulting in bactericidal activity (≥ 3 log kill) in the model for both OXA and CFZ. In contrast, neither in vitro-defined NaHCO3-nonresponsive MRSA strains showed significant sensitization in the SEV model to either β-lactam. At both NaHCO3 concentrations, the fractional time-above-MIC was >50% for both CFZ and OXA in the NaHCO3-responsive MRSA. Also, in RPMI+10% LB media (proposed as a more host-mimicking microenvironment and containing 25 mM NaHCO3), both CFZ and OXA exhibited enhanced bactericidal activity against each NaHCO3-responsive strain in the SEV model. Neither CFZ nor OXA exposures selected for high-level β-lactam-resistant mutants within SEVs. Thus, in this ex vivo model of endocarditis, in the presence of NaHCO3 supplementation, both CFZ and OXA are highly active against MRSA strains that demonstrate similar enhanced susceptibility in NaHCO3-supplemented media in vitro.

scholarly journals Ability of Bicarbonate Supplementation To Sensitize Selected Methicillin-Resistant Staphylococcus aureus Strains to β-Lactam Antibiotics in an Ex Vivo Simulated Endocardial Vegetation Model

2019 ◽  
Vol 64 (3) ◽  
Author(s):  
Warren E. Rose ◽  
Ana M. Bienvenida ◽  
Yan Q. Xiong ◽  
Henry F. Chambers ◽  
Arnold S. Bayer ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Bactericidal Activity ◽  
Ex Vivo ◽  
Rabbit Model ◽  
Luria Bertani ◽  
Growth Media ◽  
Methicillin Resistant ◽  
Content Type ◽  
Mrsa Strains

ABSTRACT Supplementation of standard growth media (cation-adjusted Mueller-Hinton Broth [CAMHB]) with bicarbonate (NaHCO3) increases β-lactam susceptibility of selected methicillin-resistant Staphylococcus aureus (MRSA) strains (“NaHCO3 responsive”). This “sensitization” phenomenon translated to enhanced β-lactam efficacy in a rabbit model of endocarditis. The present study evaluated NaHCO3-mediated β-lactam MRSA sensitization using an ex vivo pharmacodynamic model, featuring simulated endocardial vegetations (SEVs), to more closely mimic the host microenvironment. Four previously described MRSA strains were used: two each exhibiting in vitro NaHCO3-responsive or NaHCO3-nonresponsive phenotypes. Cefazolin (CFZ) and oxacillin (OXA) were evaluated in CAMHB with or without NaHCO3. Intra-SEV MRSA killing was determined over 72-h exposures. In both “responsive” strains, supplementation with 25 mM or 44 mM NaHCO3 significantly reduced β-lactam MICs to below the OXA susceptibility breakpoint (≤4 mg/liter) and resulted in bactericidal activity (≥3-log killing) in the model for both OXA and CFZ. In contrast, neither in vitro-defined nonresponsive MRSA strain showed significant sensitization in the SEV model to either β-lactam. At both NaHCO3 concentrations, the fractional time above MIC was >50% for both CFZ and OXA in the responsive MRSA strains. Also, in media containing RPMI plus 10% Luria-Bertani broth (proposed as a more host-mimicking microenvironment and containing 25 mM NaHCO3), both CFZ and OXA exhibited enhanced bactericidal activity against NaHCO3-responsive strains in the SEV model. Neither CFZ nor OXA exposures selected for emergence of high-level β-lactam-resistant mutants within SEVs. Thus, in this ex vivo model of endocarditis, in the presence of NaHCO3 supplementation, both CFZ and OXA are highly active against MRSA strains that demonstrate similar enhanced susceptibility in NaHCO3-supplemented media in vitro.

scholarly journals In Vitro and Ex Vivo Activities of Minocycline and EDTA against Microorganisms Embedded in Biofilm on Catheter Surfaces

2003 ◽  
Vol 47 (11) ◽  
pp. 3580-3585 ◽  
Author(s):  
Issam Raad ◽  
Ioannis Chatzinikolaou ◽  
Gassan Chaiban ◽  
Hend Hanna ◽  
Ray Hachem ◽  
...  
Keyword(s):  
Low Dose ◽  
Ex Vivo ◽  
Bacterial Colonization ◽  
Rabbit Model ◽  
Confocal Laser ◽  
High Dose ◽  
High Concentration ◽  
Ex Vivo Model ◽  
Highly Active

ABSTRACT Minocycline-EDTA (M-EDTA) flush solution has been shown to prevent catheter-related infection and colonization in a rabbit model and in hemodialysis patients. We undertook this study in order to determine the activities of M-EDTA against organisms embedded in fresh biofilm (in vitro) and mature biofilm (ex vivo). For the experiment with the in vitro model, a modified Robbin’s device (MRD) was used whereby 25 catheter segments were flushed for 18 h with 106 CFU of biofilm-producing Staphylococcus epidermidis, Staphyloccocus aureus, and Candida albicans per ml. Subsequently, each of the catheter segments was incubated in one of the following solutions: (i) streptokinase, (ii) heparin, (iii) broth alone, (iv) vancomycin, (v) vancomycin-heparin, (vi) EDTA, (vii) minocycline (high-dose alternating with low-dose), or (viii) M-EDTA (low-dose minocycline alternating with high-dose minocycline were used to study the additive and synergistic activities of M-EDTA). All segments were cultured quantitatively by scrape sonication. For the experiment with the ex vivo model, 54 catheter tip segments removed from patients and colonized with bacterial organisms by roll plate were longitudinally cut into two equal segments and exposed to either saline, heparin, EDTA, or M-EDTA (with high-dose minocycline). Subsequently, all segments were examined by confocal laser electron microscopy. In the in vitro MRD model, M-EDTA (with a low concentration of minocycline) was significantly more effective than any other agent in reducing colonization of S. epidermidis, S. aureus, and C. albicans (P < 0.01). M-EDTA (with a high concentration of minocycline) eradicated all staphylococcal and C. albicans organisms embedded in the biofilm. In the ex vivo model, M-EDTA (with a high concentration of minocycline) reduced bacterial colonization more frequently than EDTA or heparin (P < 0.01). We concluded that M-EDTA is highly active in eradicating microorganisms embedded in fresh and mature biofilm adhering to catheter surfaces.

scholarly journals The Combination of Daptomycin and Fosfomycin Has Synergistic, Potent, and Rapid Bactericidal Activity against Methicillin-ResistantStaphylococcus aureusin a Rabbit Model of Experimental Endocarditis

2018 ◽  
Vol 62 (6) ◽  
Author(s):  
Cristina García-de-la-Mària ◽  
Oriol Gasch ◽  
Javier García-Gonzalez ◽  
Dolors Soy ◽  
Evelyn Shaw ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Bactericidal Activity ◽  
Combined Therapy ◽  
Rabbit Model ◽  
Bactericidal Effect ◽  
Methicillin Resistant ◽  
Content Type ◽  
Mrsa Strains ◽  
Time Kill

ABSTRACTWe investigated whether the addition of fosfomycin or cloxacillin to daptomycin provides better outcomes in the treatment of methicillin-resistantStaphylococcus aureus(MRSA) experimental aortic endocarditis in rabbits. Five MRSA strains were used to performin vitrotime-kill studies using standard (106) and high (108) inocula. Combined therapy was compared to daptomycin monotherapy treatment in the MRSA experimental endocarditis model. A human-like pharmacokinetics model was applied, and the equivalents of cloxacillin at 2 g/4 h, fosfomycin at 2 g/6 h, and daptomycin at 6 to 10 mg/kg/day were administered intravenously. A combination of daptomycin and either fosfomycin or cloxacillin was synergistic in the five strains tested at both inocula. A bactericidal effect was detected in four of five strains tested with both combinations. The MRSA-277 strain (vancomycin MIC, 2 μg/ml) was used for the experimental endocarditis model. Daptomycin plus fosfomycin significantly improved the efficacy of daptomycin monotherapy at 6 mg/kg/day in terms of both the proportion of sterile vegetations (100% versus 72%,P= 0.046) and the decrease in the density of bacteria within the vegetations (P= 0.025). Daptomycin plus fosfomycin was as effective as daptomycin monotherapy at 10 mg/kg/day (100% versus 93%,P= 1.00) and had activity similar to that of daptomycin plus cloxacillin when daptomycin was administered at 6 mg/kg/day (100% versus 88%,P= 0.48). Daptomycin nonsusceptibility was not detected in any of the isolates recovered from vegetations. In conclusion, for the treatment of MRSA experimental endocarditis, the combination of daptomycin plus fosfomycin showed synergistic and bactericidal activity.

scholarly journals Newly developed dual topoisomerase inhibitor P8-D6 is highly active in ovarian cancer

2021 ◽  
Vol 13 ◽  
pp. 175883592110598
Author(s):  
Inken Flörkemeier ◽  
Tamara N. Steinhauer ◽  
Nina Hedemann ◽  
Magnus Ölander ◽  
Per Artursson ◽  
...  
Keyword(s):  
Ovarian Cancer ◽  
Topoisomerase I ◽  
Ex Vivo ◽  
Chemotherapy Resistance ◽  
Membrane Integrity ◽  
Three Dimensional ◽  
New Drugs ◽  
Highly Active ◽  
Gynaecologic Neoplasms

Background: Ovarian cancer (OvCa) constitutes a rare and highly aggressive malignancy and is one of the most lethal of all gynaecologic neoplasms. Due to chemotherapy resistance and treatment limitations because of side effects, OvCa is still not sufficiently treatable. Hence, new drugs for OvCa therapy such as P8-D6 with promising antitumour properties have a high clinical need. The benzo[ c]phenanthridine P8-D6 is an effective inductor of apoptosis by acting as a dual topoisomerase I/II inhibitor. Methods: In the present study, the effectiveness of P8-D6 on OvCa was investigated in vitro. In various OvCa cell lines and ex vivo primary cells, the apoptosis induction compared with standard therapeutic agents was determined in two-dimensional monolayers. Expanded by three-dimensional and co-culture, the P8-D6 treated cells were examined for changes in cytotoxicity, apoptosis rate and membrane integrity via scanning electron microscopy (SEM). Likewise, the effects of P8-D6 on non-cancer human ovarian surface epithelial cells and primary human hepatocytes were determined. Results: This study shows a significant P8-D6-induced increase in apoptosis and cytotoxicity in OvCa cells which surpasses the efficacy of well-established drugs like cisplatin or the topoisomerase inhibitors etoposide and topotecan. Non-cancer cells were affected only slightly by P8-D6. Moreover, no hepatotoxic effect in in vitro studies was detected. Conclusion: P8-D6 is a strong and rapid inductor of apoptosis and might be a novel treatment option for OvCa therapy.

scholarly journals In Vitro Activity of S-3578, a New Broad-Spectrum Cephalosporin Active against Methicillin-Resistant Staphylococci

2003 ◽  
Vol 47 (3) ◽  
pp. 923-931 ◽  
Author(s):  
Takaji Fujimura ◽  
Yoshinori Yamano ◽  
Isamu Yoshida ◽  
Jingoro Shimada ◽  
Shogo Kuwahara
Keyword(s):  
Antibacterial Activity ◽  
Population Analysis ◽  
Low Frequency ◽  
Methicillin Resistant ◽  
Gram Positive Bacteria ◽  
Highly Active ◽  
In Vitro Antibacterial Activity ◽  
Mrsa Strains ◽  
Time Kill

ABSTRACT The in vitro antibacterial activity of S-3578, a new parenteral cephalosporin, against clinical isolates was evaluated. The MICs of the drug at which 90% of the isolates were inhibited were 4 μg/ml for methicillin-resistant Staphylococcus aureus (MRSA) and 2 μg/ml for methicillin-resistant Staphylococcus epidermidis, which were fourfold higher than and equal to those of vancomycin, respectively. The anti-MRSA activity of S-3578 was considered to be due to its high affinity for penicillin-binding protein 2a (50% inhibitory concentration, 4.5 μg/ml). In time-kill studies with 10 strains each of MRSA and methicillin-susceptible S. aureus, S-3578 caused more than a 4-log10 decrease of viable cells on the average at twice the MIC after 24 h of exposure, indicating that it had potent bactericidal activity. Furthermore, in population analysis of MRSA strains with heterogeneous or homogeneous resistance to imipenem, no colonies emerged from about 109 cells on agar plates containing twice the MIC of S-3578, suggesting the low frequency of emergence of S-3578-resistant strains from MRSA. S-3578 was also highly active against penicillin-resistant Streptococcus pneumoniae (PRSP), with a MIC90 of 1 μg/ml, which was comparable to that of ceftriaxone. S-3578 also had antibacterial activity against a variety of gram-negative bacteria including Pseudomonas aeruginosa, though its activity was not superior to that of cefepime. In conclusion, S-3578 exhibited a broad antibacterial spectrum and, particularly, had excellent activity against gram-positive bacteria including methicillin-resistant staphylococci and PRSP. Thus, S-3578 was considered to be worthy of further evaluation.

ANTITHROMBOTIC ACTIONS OF A SULFOMUCOPOLYSACCHARIDE MIXTURE (ATERIOD) IN ANIMAL MODELS

1987 ◽  
Author(s):  
U Cornelli ◽  
J M Welena ◽  
J Fareed ◽  
X Huan ◽  
D Hoppensteadt
Keyword(s):  
Time Course ◽  
Ex Vivo ◽  
Rabbit Model ◽  
Factor Xa ◽  
Heparin Cofactor Ii ◽  
Platelet Factor ◽  
Thrombosis Model ◽  
Mucosal Lining ◽  
Cellular Modifications

Ateriod obtained from beef mucosal lining is a sulfomuco-polysaccharide mixture of various glycosaminoglycans which contains derma tans, heparatans and traces of heparin. It has been used in the treatment ofatherosclerosis and related vaso-oclusive disorders. Ateriod is standardized in terms of its lipoprotein lipase activation actions. Ateriod contains signfi-cant in vitro anticoagulant and antiprotease (anti-factor Xa and anti-factor Ila) activities as measured by clot-based and chromr ogenic substrate methods. However, this in vitro activity is 7-10 times lesser than heparin. In order to study the antithrombotic actions of this agent in subcutaneous, intravenous and oral routes, we utilized a rabbit stasis thrombosis model with a prothrombin complex concentrate/Russell's viper venom thrombogenic challenge and prolonged stasis. The apparent ED50 for the antithrombotic action were found to be: IV (75-100 ug/ kg), SC (0.8-1.3 mg/kg) and oral (20-30 mg/kg). In both the IV- and SC studies, sustained anticoagulant and antiprotease actions were evident. The observed antithrombotic actions did not relate to the anti-factor IIa or anti-factor Xa actions. Pretreatment of Ateriod with equigravimetric amounts of protamine and platelet factor 4 did not neutralize the antithrombotic actions of this agent in the rabbit model. In a primate (Macaca mulatta) model of pharmacokinetics, ex vivo analysis following subcutaneously administered Ateriod showed sustained anticoagulant and antiprotease effects. The time course of the subcutaneously administered Ateriod was markedly different than heparin and a low molecular weight heparin. Treated animals were shown to resist induced hypercoagulability following injection of homologous serum as measured by FPA generation for extended periods. These studies suggest that Ateriod produces a strong antithrombotic action and that it has highly sustained pharmacokinetics. The antithrombotic activity appears to be primarily mediated via non-antithrombin - HI dependent events which may be related to heparin cofactor II and vascular/ cellular modifications.

scholarly journals Influence of Conditioned Media on the Re-Differentiation Capacity of Human Chondrocytes in 3D Spheroid Cultures

2020 ◽  
Vol 9 (9) ◽  
pp. 2798
Author(s):  
Annett Klinder ◽  
Sophie Kussauer ◽  
Bettina Hiemer ◽  
Andreas Wree ◽  
Rainer Bader ◽  
...  
Keyword(s):  
Conditioned Medium ◽  
Culture Media ◽  
Ex Vivo ◽  
Cartilage Matrix ◽  
Human Chondrocytes ◽  
Growth Media ◽  
Cell Cultivation ◽  
Cell Based Therapy ◽  
Tgf Β1

A major challenge of cell-based therapy for cartilage lesions is the preservation of the chondrogenic phenotype during ex vivo cell cultivation. In this in vitro study, the chondro-inductive capacity of two different hyaline cartilage-conditioned cell culture media on human chondrocytes in 3D spheroids was determined. Media were conditioned by incubation of 200 mg/mL vital or devitalized cartilage matrix in growth media over 35 days. The media were analyzed for the content of soluble procollagen type (Col) II and glycosaminoglycans (GAGs) as well as released TGF-β1, IGF-1 and IGFBP3. Unconditioned medium served as a negative control while the positive medium control was supplemented with TGF-β1 and IGF-1. Spheroid cultures prepared from human chondrocytes were cultivated at 37 °C, 5% CO2 and 21% O2 in the respective media and controls. After 14 and 35 days, the deposition of ECM components was evaluated by histological analysis. Vital cartilage-conditioned medium contained significantly higher levels of Col II and active TGF-β1 compared to medium conditioned with the devitalized cartilage matrix. Despite these differences, the incubation with vital as well as devitalized cartilage conditioned medium led to similar results in terms of deposition of proteoglycans and collagen type II, which was used as an indicator of re-differentiation of human chondrocytes in spheroid cultures. However, high density 3D cell cultivation showed a positive influence on re-differentiation.

scholarly journals Pharmacodynamics and Bactericidal Activity of Moxifloxacin in Experimental Escherichia coliMeningitis

2001 ◽  
Vol 45 (11) ◽  
pp. 3092-3097 ◽  
Author(s):  
Violeta Rodriguez-Cerrato ◽  
Cynthia C. McCoig ◽  
Ian C. Michelow ◽  
Faryal Ghaffar ◽  
Hasan S. Jafri ◽  
...  
Keyword(s):  
Bactericidal Activity ◽  
Rabbit Model ◽  
Time Curve ◽  
Bacterial Killing ◽  
E Coli ◽  
Pharmacodynamic Profile ◽  
Spectrum Activity ◽  
Csf Concentration ◽  
Broad Spectrum Activity

ABSTRACT Moxifloxacin, an 8-methoxyquinolone with broad-spectrum activity in vitro, was studied in the rabbit model of Escherichia colimeningitis. The purposes of this study were to evaluate the bactericidal effectiveness and the pharmacodynamic profile of moxifloxacin in cerebrospinal fluid (CSF) and to compare the bactericidal activity with that of ceftriaxone and meropenem therapy. After induction of meningitis, animals were given single doses of 10, 20, and 40 mg/kg or divided-dose regimens of 5, 10, and 20 mg/kg twice, separated by 6 h. After single doses, the penetration of moxifloxacin into purulent CSF, measured as percentage of the area under the concentration-time curve (AUC) in CSF relative to the AUC in plasma, was approximately 50%. After single doses of 10, 20, and 40 mg/kg, the maximum CSF concentration (C max) values were 1.8, 4.2, and 4.9 μg/ml, respectively; the AUC values (total drug) were 13.4, 25.4, and 27.1 μg/ml · h, respectively, and the half-life values (t ½) were 6.7, 6.6, and 4.7 h, respectively. The bacterial killing in CSF for moxifloxacin, calculated as the Δlog10 CFU per milliliter per hour, at 3, 6, and 12 h after single doses of 10, 20, and 40 mg/kg were −5.70, −6.62, and −7.02; −7.37, −7.37, and −6.87; and −6.62, −6.62, and −6.62, respectively, whereas those of ceftriaxone and meropenem were −4.18, −5.24, and −4.43, and −3.64, −3.59, and −4.12, respectively. The CSF pharmacodynamic indices of AUC/MBC and C max/MBC were interrelated (r = 0.81); there was less correlation withT > MBC (r = 0.74). In this model, therapy with moxifloxacin appears to be at least as effective as ceftriaxone and more effective than meropenem therapy in eradicatingE. coli from CSF.

Rapid Ex Vivo Expansion of CMV Specific CTL Suitable for Clinical Immunotherapy Using CpG-DNA Matured PBMC Infected with Recombinant MVA.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 5102-5102
Author(s):  
Don J. Diamond ◽  
Zhongde Wang ◽  
Simon F. Lacey ◽  
Corinna La Rosa
Keyword(s):  
T Cells ◽  
Cd8 T Cells ◽  
Ex Vivo ◽  
Attractive Alternative ◽  
Memory Cd8 T Cells ◽  
Equal Importance ◽  
High Level ◽  
Cellular Immune ◽  
Antigen Presenting

Abstract Adoptive transfer of ex vivo expanded CMV-specific T cells is an effective approach, and an attractive alternative to using anti-virals to manage CMV infection for HSCT recipients. We recently published a robust approach to expanding CMV-specific CTL based on infection of autologous EBV-LCL with the attenuated poxvirus, Modified Vaccinia Ankara (MVA), expressing CMV pp65, pp150, and IE1 proteins. This approach causes vigorous, up to 500fold expansions in as little as 12–14 days of memory CD8+ T cells specific for these immunodominant antigens. In order to improve the specificity of the expanded T cells, a method was sought to derive effective antigen presenting cells (APC) that avoided the use of EBV-LCL. Of equal importance is to develop an expansion approach that avoids the need to involve virally infected APC in developing a clinical product. Our preliminary observation is that rMVA can infect PBMC in vitro, causing high levels of expression of recombinant CMV antigens. To be permissible for high level expression from rMVA, fresh PBMC were treated with different combinations of single-stranded CpG-containing phosphorothioate backbone oligonucleotides (ODN). A three-day incubation with a combination of two ODN (ODN # 2006 and 2216) which are known to stimulate both plasmacytoid dendritic and B-cells were found to reproducibly generate a highly rMVA infectable population of PBMC. In all five healthy CMV-positive donors tested, CpG ODN treated autologous PBMC, infected with recombinant rMVA, elicited a 20-fold average expansion of CMV-specific CD8+ T cells, in 10 days. Several different rMVA expressing CMV genes were evaluated, including a novel vector expressing the UL44 gene product, an immunodominant target of the host cellular immune response. The expanded T cell populations showed minimal alloreactivity, and exhibited high levels of CMV-specific MHC Class I tetramer binding, epitope-specific cytokine production, and cytotoxic activity. The availability of a source of autologous professional APC that can be used after only 3 days of priming, enhances the attractiveness of using rMVA for adoptive immunotherapy for HSCT recipients or donor vaccination.

scholarly journals Synergy of Daptomycin with Oxacillin and Other β-Lactams against Methicillin-Resistant Staphylococcus aureus

2004 ◽  
Vol 48 (8) ◽  
pp. 2871-2875 ◽  
Author(s):  
Kenneth H. Rand ◽  
Herbert J. Houck
Keyword(s):  
Staphylococcus Aureus ◽  
Bactericidal Activity ◽  
Screening Method ◽  
Methicillin Resistant ◽  
Drug Concentrations ◽  
Mueller Hinton ◽  
Mueller Hinton Agar ◽  
High Level ◽  
Time Kill

ABSTRACT We previously observed marked synergy between daptomycin and both rifampin and ampicillin against vancomycin-resistant enterococci (VRE). Because the synergy between daptomycin and ampicillin was observed for 100% of VRE strains with high-level ampicillin resistance (ampicillin MIC of ≥128 μg/ml), we looked for synergy between daptomycin and other β-lactams against 18 strains of methicillin-resistant Staphylococcus aureus (MRSA) by employing a time-kill method using Mueller-Hinton broth supplemented to 50 mg of Ca2+/liter. All strains were resistant to oxacillin (16 of 18 strains were resistant at drug concentrations of ≥256 μg/ml), and all strains were susceptible to daptomycin (the MIC at which 90% of the tested isolates were inhibited was 1 μg/ml). Daptomycin was tested at concentrations of 2, 1, 0.5, 0.25, 0.125, and 0.0625 μg/ml alone or in combination with oxacillin at a fixed concentration of 32 μg/ml. Synergy was found for all 18 strains with daptomycin at one-half the MIC in combination with 32 μg of oxacillin/ml, and synergy was found for 11 of 18 strains (61%) with daptomycin at one-fourth the MIC or less in combination with oxacillin. At 24 h, the daptomycin-oxacillin combination with daptomycin at one-half the MIC showed bactericidal activity against all 18 strains, and the combination with one-fourth the daptomycin MIC showed bactericidal activity against 9 of 18 strains. We also used a novel screening method to look for synergy between daptomycin and other β-lactams. In this approach, daptomycin was incorporated into Ca2+-supplemented Mueller-Hinton agar at subinhibitory concentrations, and synergy was screened by comparing test antibiotic Kirby-Bauer disks on agar with and without daptomycin. By this method, daptomycin with ampicillin-sulbactam, ticarcillin-clavulanate, or piperacillin-tazobactam showed synergy comparable to or greater than daptomycin with oxacillin. For seven of the eight strains tested, time-kill studies confirmed synergy between daptomycin and ampicillin-sulbactam with ampicillin in the range of 2 to 8 μg/ml. The combination of daptomycin and β-lactams may be useful for the treatment of MRSA infection, but further studies are needed to elucidate the mechanisms and to determine the in vivo efficacy of the combination.

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