The ability of daptomycin to produce bactericidal activity against Staphylococcus aureus while causing negligible cell lysis has been demonstrated using electron microscopy and the membrane integrity probes calcein and ToPro3. The formation of aberrant septa on the cell wall, suggestive of impairment of the cell division machinery, was also observed.Many antibiotics derive bactericidal activity from their ability to lyse cells, which may cause liberation of potent proinflammatory bacterial components, resulting in the generation of a robust innate immune response that can potentially cause harm to the host (8). The lipopeptide antibiotic daptomycin is active against a wide range of gram-positive bacteria (Cubicin prescription information, 2005; Cubist Pharmaceuticals, Lexington, MA) (4) and is believed to possess a novel mechanism of action that does not involve cell lysis. Instead, the lipophilic acyl tail of daptomycin is inserted into the cytoplasmic membrane of the bacterium, leading to potassium efflux; destruction of the ion-concentration gradient; membrane depolarization; inhibition of protein, DNA, and RNA synthesis; and finally cell death (Cubicin prescription information, 2005; Cubist Pharmaceuticals, Lexington, MA) (5, 11, 13). Daptomycin is rapidly bactericidal in vitro against Staphylococcus aureus at low multiples of the MIC (12). Here, we demonstrate the bactericidal activity of daptomycin against S. aureus in the absence of cell lysis. (Portions of this work were presented previously at the 43rd Interscience Conference on Antimicrobial Agents and Chemotherapy [10].)Cell lysis was initially monitored by measuring optical density during log-phase time kills. Late-exponential-phase cultures (approximately 10 8 CFU/ml) were used to allow samples to be obtained for transmission electron microscopy (TEM). Staphylococcus aureus ATCC 29213 was grown overnight in calcium-supplemented Mueller-Hinton broth (MHBc; 50 mg/ liter Ca 2ϩ ) and subcultured 1:1,000 into fresh MHBc. Cultures were grown at 37°C with shaking (200 rpm) to an optical density at 600 nm (OD 600 ) of 0.3 to ensure sufficient biomass for fixation and processing. Daptomycin was added at multiples (1ϫ to 8ϫ) of the MIC (0.5 g/ml). At the indicated time points, samples were removed, OD 600 and number of CFU/ml were measured as previously described (7), and cells were pelleted and resuspended in 1 ml MHBc plus 2.5% (vol/vol) glutaraldehyde. Glutaraldehyde-fixed samples were postfixed in 2.0% (wt/vol) osmium tetroxide, followed by en bloc staining with 2.0% (wt/vol) uranyl acetate. The cells were then dehydrated through an ethanol series and embedded in LR White resin. Samples were thin sectioned and stained by uranyl acetate; lead citrate TEM was performed using a LEO 912AB microscope under standard operating conditions at 100 kV, with a liquid nitrogen anticontaminator in place.As shown in Fig. 1, at 4 g/ml, daptomycin was rapidly bactericidal, producing a Ͼ1,000-fold decrease in viability in less than 120 min, with no concomitant drop in OD 6...
Urinary tract infections (UTIs) caused by Escherichia coli have been historically managed with oral antibiotics including the cephalosporins, fluoroquinolones and trimethoprim-sulfamethoxazole. The use of these agents is being compromised by the increase in extended spectrum β-lactamase (ESBL)-producing organisms, mostly caused by the emergence and clonal expansion of E. coli multilocus sequence typing (ST) 131. In addition, ESBL isolates show co-resistance to many of oral agents. Management of UTIs caused by ESBL and fluoroquinolone-resistant organisms is becoming increasingly challenging to treat outside of the hospital setting with clinicians having to resort to intravenous agents. The aim of this study was to assess the prevalence of ESBL phenotypes and genotypes among UTI isolates of E. coli collected in the US during 2017 as well as the impact of co-resistance to oral agents such as the fluoroquinolones and trimethoprim-sulfamethoxazole. The national prevalence of ESBL phenotypes of E. coli was 15.7% and was geographically distributed across all nine Census regions. Levofloxacin and trimethoprim-sulfamethoxazole-resistance rates were ≥ 24% among all isolates and this co-resistance phenotype was considerably higher among isolates showing an ESBL phenotype (≥ 59.2%) and carrying blaCTX-M-15 (≥ 69.5%). The agents with the highest potency against UTI isolates of E. coli, including ESBL isolates showing cross-resistance across oral agents, were the intravenous carbapenems. The results of this study indicate that new oral options with the spectrum and potency similar to the intravenous carbapenems would address a significant unmet need for the treatment of UTIs in an era of emergence and clonal expansion of ESBL isolates resistant to several classes of antimicrobial agents, including oral options.
Therapeutics targeting Gram-negative bacteria have the challenge of overcoming a formidable outer membrane (OM) barrier. Here, we characterize the action of SPR741, a novel polymyxin B (PMB) analogue shown to potentiate several large-scaffold antibiotics in Gram-negative pathogens. Probing the surface topology of Escherichia coli using atomic force microscopy revealed substantial OM disorder at concentrations of SPR741 that lead to antibiotic potentiation. Conversely, very little cytoplasmic membrane depolarization was observed at these same concentrations, indicating that SPR741 acts predominately on the OM. Truncating the lipopolysaccharide (LPS) core with genetic perturbations uniquely sensitized E. coli to SPR741, suggesting that LPS core residues keep SPR741 at the OM, where it can potentiate a codrug, rather than permit its entry to the cytoplasmic membrane. Further, a promoter activity assay revealed that SPR741 challenge induced the expression of RcsAB, a stress sensor for OM perturbation. Together, these results indicate that SPR741 interacts predominately with the OM, in contrast to the dual action of PMB and colistin at both the outer and cytoplasmic membranes.
Tebipenem pivoxil HBr (TBPM-PI-HBr) is a novel orally bioavailable carbapenem. The active moiety is tebipenem. Tebipenem pivoxil is licensed for use in Japan in children with ear, nose, and throat infections and respiratory infections. The HBr salt was designed to improve drug substance and drug product properties, including stability. TBPM-PI-HBr is now being developed as an agent for the treatment of complicated urinary tract infections (cUTI) in adults. The pharmacokinetics-pharmacodynamics of tebipenem were studied in a well-characterized neutropenic murine thigh infection model. Plasma drug concentrations were measured using liquid chromatography-tandem mass spectrometry. Dose fractionation experiments were performed after establishing dose-response relationships. The magnitude of drug exposure required for stasis was established using 11 strains of Enterobacteriaceae (Escherichia coli, n = 6; Klebsiella pneumoniae, n = 5) with a variety of resistance mechanisms. The relationship between drug exposure and the emergence of resistance was established in a hollow-fiber infection model (HFIM). Tebipenem exhibited time-dependent pharmacodynamics that were best described by the free drug area under the concentration-time curve (fAUC0-24)/MIC corrected for the length of the dosing interval (fAUC0–24/MIC · 1/tau). The pharmacodynamics of tebipenem versus E. coli and K. pneumoniae were comparable, as was the response of strains possessing extended-spectrum β-lactamases versus the wild type. The median fAUC0-24/MIC · 1/tau value for the achievement of stasis in the 11 strains was 23. Progressively more fractionated regimens in the HFIM resulted in the suppression of resistance. An fAUC0-24/MIC · 1/tau value of 34.58 to 51.87 resulted in logarithmic killing and the suppression of resistance. These data and analyses will be used to define the regimen for a phase III study of adult patients with cUTI.
The antimicrobial activity of tebipenem and other carbapenem agents were tested in vitro against a set of recent clinical isolates responsible for urinary tract infection (UTI), as well as against a challenge set. Isolates were tested by reference broth microdilution and included Escherichia coli (101 isolates), Klebsiella pneumoniae (208 isolates), and Proteus mirabilis (103 isolates) species. Within each species tested, tebipenem showed equivalent MIC 50/90 values to those of meropenem (E. coli MIC 50/90 , Յ0.015/0.03 mg/liter; K. pneumoniae MIC 50/90 , 0.03/0.06 mg/liter; and P. mirabilis MIC 50/90 , 0.06/0.12 mg/liter) and consistently displayed MIC 90 values 8-fold lower than imipenem. Tebipenem and meropenem (MIC 50 , 0.03 mg/liter) showed equivalent MIC 50 results against wild-type, AmpC-, and/or extended-spectrum -lactamase (ESBL)-producing isolates. Tebipenem also displayed MIC 50/90 values 4to 8-fold lower than imipenem against the challenge set. All carbapenem agents were less active (MIC 50 , Ն8 mg/liter) against isolates carrying carbapenemase genes. These data confirm the in vitro activity of the orally available agent tebipenem against prevalent UTI Enterobacteriaceae species, including those producing ESBLs and/or plasmid AmpC enzymes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.