219 research outputs found

    Activity of nacubactam (RG6080/OP0595) combinations against metallo-β-lactamase (MBL)-producing Enterobacteriaceae

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    Background: Diazabicyclooctanes (DBOs) are promising β-lactamase inhibitors. Some, including nacubactam (OP0595/RG6080), also bind PBP2 and have an enhancer effect, allowing activity against Enterobacteriaceae with MBLs, which DBOs do not inhibit. We tested the activity of nacubactam/β-lactam combinations against MBL-producing Enterobacteriaceae. Methods: Test panels comprised (i) 210 consecutive Enterobacteriaceae with NDM or VIM MBLs, as referred by UK diagnostic laboratories, and (ii) 99 supplementary MBL-producing Enterobacteriaceae, representing less prevalent phenotypes, species and enzymes. MICs were determined by CLSI agar dilution. Results: MICs of nacubactam alone were bimodal, clustering at 1–8 mg/L or >32 mg/L; >85% of values for Escherichia coli and Enterobacter spp. fell into the low MIC cluster, whereas Proteeae were universally resistant and the Klebsiella spp. were divided between the two groups. Depending on the prospective breakpoint (4 + 4 or 8 + 4 mg/L), and on whether all isolates were considered or solely the Consecutive Collection, meropenem/nacubactam and cefepime/nacubactam inhibited 80.3%–93.3% of MBL producers, with substantial gains over nacubactam alone. Against the most resistant isolates (comprising 57 organisms with MICs of nacubactam >32 mg/L, cefepime ≥128 mg/L and meropenem ≥128 mg/L), cefepime/nacubactam at 8 + 4 mg/L inhibited 63.2% and meropenem/nacubactam at 8 + 4 mg/L inhibited 43.9%. Aztreonam/nacubactam, incorporating an MBL-stable β-lactam partner, was almost universally active against the MBL producers and, unlike aztreonam/avibactam, had an enhancer effect. Conclusions: Nacubactam combinations, including those using MBL-labile β-lactams, e.g. meropenem and cefepime, can overcome most MBL-mediated resistance. This behaviour reflects nacubactam’s direct antibacterial and enhancer activity

    In vitro activity of cefepime/zidebactam (WCK 5222) against Gram-negative bacteria

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    Background: Diazabicyclooctanes (DBOs) inhibit class A, class C and some class D β-lactamases. A few also bind PBP2, conferring direct antibacterial activity and a β-lactamase-independent ‘enhancer' effect, potentiating β-lactams targeting PBP3. We tested a novel DBO, zidebactam, combined with cefepime. Methods: CLSI agar dilution MICs were determined with cefepime/zidebactam in a chequerboard format. Bactericidal activity was also measured. Results: Zidebactam MICs were ≤2 mg/L (mostly 0.12–0.5 mg/L) for most Escherichia coli, Klebsiella, Citrobacter and Enterobacter spp., but were >32 mg/L for Proteeae, most Serratia and a few E. coli, Klebsiella and Enterobacter/Citrobacter. The antibacterial activity of zidebactam dominated chequerboard studies for Enterobacteriaceae, but potentiation of cefepime was apparent for zidebactam-resistant isolates with class A and C enzymes, illustrating β-lactamase inhibition. Overall, cefepime/zidebactam inhibited almost all Enterobacteriaceae with AmpC, ESBL, K1, KPC and OXA-48-like β-lactamases at 1 + 1 mg/L and also 29 of 35 isolates with metallo-carbapenemases, including several resistant to zidebactam alone. Zidebactam MICs for 36 of 50 Pseudomonas aeruginosa were 4–16 mg/L, and the majority of AmpC, metallo-β-lactamase-producing and cystic fibrosis isolates were susceptible to cefepime/zidebactam at 8 + 8 mg/L. Zidebactam MICs for Acinetobacter baumannii and Stenotrophomonas maltophilia were >32 mg/L; potentiation of cefepime was frequent for S. maltophilia, but minimal for A. baumannii. Kill curve results largely supported MICs. Conclusion: Zidebactam represents a second triple-action DBO following RG6080, with lower MICs for Enterobacteriaceae and P. aeruginosa. Clinical evaluation of cefepime/zidebactam must critically evaluate the reliance that can be placed on this direct antibacterial activity and on the enhancer effect as well as β-lactamase inhibition

    Activity of RX-04 Pyrrolocytosine Protein Synthesis Inhibitors against Multidrug-Resistant Gram-Negative Bacteria

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    Pyrrolocytosines RX-04A-D are designed to bind to the bacterial 50S ribosomal subunit differently from currently-used antibiotics. The four analogs had broad anti-Gram-negative activity: RX-04A inhibited 94.7% of clinical Enterobacteriaceae, Acinetobacter baumannii and Pseudomonas aeruginosa at 0.5-4 μg/ml, with no MICs >8 μg/ml. MICs for multi-resistant carbapenemase producers were up to two-fold higher than for control strains, with values ≥8 μg/ml for one Serratia isolate with porin and efflux lesions. mcr-1 did not affect MICs

    WCK 4234, a novel diazabicyclooctane potentiating carbapenems against Enterobacteriaceae, Pseudomonas and Acinetobacter with class A, C and D β-lactamases

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    Background: Several diazabicyclooctanes (DBOs) are under development as inhibitors of Class A and C -lactamases. Inhibition of OXA (Class D) carbapenemases is variable, with those of Acinetobacter spp. remaining notably resistant. We describe a novel DBO, WCK 4234 (Wockhardt), with distinctive activity against OXA carbapenemases.  Methods: MICs of imipenem and meropenem were determined by CLSI agar dilution with WCK 4234 added at 4 or 8 mg/L. Test organisms were clinical Enterobacteriaceae, Acinetobacter baumannii and Pseudomonas aeruginosa with carbapenemases or carbapenem resistance via porin loss plus AmpC or ESBL activity. AmpC mutants were also tested.  Results: WCK 4234, which lacked direct antibacterial activity, strongly potentiated imipenem and meropenem against Enterobacteriaceae with OXA-48/181, KPC enzymes, or with combinations of impermeability and AmpC or ESBL activity, with MICs reduced to <2 mg/L in almost all cases. Carbapenems likewise were potentiated against P. aeruginosa (n=2) with OXA-181 enzyme, with MICs reduced from 64-128 mg/L to 2-8 mg/L and against A. baumannii with OXA carbapenemases, particularly OXA-23 or hyperproduced OXA-51, with MICs reduced to <2 mg/L for 9/10 acinetobacters with OXA-23 enzyme. Carbapenems were not potentiated against Enterobacteriaceae or non-fermenters with metallo--lactamases.   Conclusion: WCK 4234 distinctively overcame resistance mediated by OXA-type carbapenemases, including in A. baumannii. It behaved similarly to other DBOs against strains with KPC carbapenemases or combinations of impermeability and ESBL or AmpC activity

    The HDAC6 Inhibitor Trichostatin A Acetylates Microtubules and Protects Axons From Excitotoxin-Induced Degeneration in a Compartmented Culture Model

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    Axon degeneration has been implicated as a pathological process in several neurodegenerative diseases and acquired forms of neural injury. We have previously shown that stabilizing microtubules can protect axons against excitotoxin-induced fragmentation, however, the alterations of microtubules following excitotoxicity that results in axon degeneration are currently unknown. Hence, this study investigated whether excitotoxicity affects the post-translational modifications of microtubules and microtubule-associated proteins, and whether reversing these changes has the potential to rescue axons from degeneration. To investigate microtubule alterations, primary mouse cortical neurons at 10 days in vitro were treated with 10 or 25 μM kainic acid to induce excitotoxicity and axon degeneration. Post-translational modifications of microtubules and associated proteins were examined at 6 h following kainic acid exposure, relative to axon degeneration. While there were no changes to tyrosinated tubulin or MAP1B, acetylated tubulin was significantly (p &lt; 0.05) decreased by 40% at 6 h post-treatment. To determine whether increasing microtubule acetylation prior to kainic acid exposure could prevent axon fragmentation, we investigated the effect of reducing microtubule deacetylation with the HDAC6 inhibitor, trichostatin A. We found that trichostatin A prevented kainic acid-induced microtubule deacetylation and significantly (p &lt; 0.05) protected axons from fragmentation. These data suggest that microtubule acetylation is a potential target for axonal protection where excitotoxicity may play a role in neuronal degeneration

    In vitro activity of cefiderocol, a siderophore-cephalosporin, against multidrug-resistant gram-negative bacteria

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    Cefiderocol is a parenteral siderophore cephalosporin, with a catechol-containing 3′ substituent. We evaluated its MICs against gram-negative bacteria, using iron-depleted Mueller-Hinton broth. The panel comprised 305 Enterobacterales, 111 P. aeruginosa and 99 A. baumannii, all selected for carbapenem resistance and multi-resistance to other agents. At 2 and 4 μg/ml cefiderocol inhibited 78.7% and 92.1% respectively of all Enterobacterales tested, with rates of 80-100% for isolates with all modes of carbapenem resistance except NDM enzymes (41.0% inhibited at 2 μg/ml, 72.1% at 4 μg/ml) or combinations of ESBL and porin-loss (61.5% inhibited at 2 μg/ml, 88.5% at 4 μg/ml). Cefiderocol also inhibited 81.1% and 86.5% of all P. aeruginosa at 2 and 4 μg/ml respectively, with rates of 80-100% for isolates with VIM, IMP, GES or VEB β-lactamases and slightly lower rates for those with NDM (45.5% at 2 μg/ml and 72.7% at 4 μg/ml) and PER (66.7% at 2 μg/ml and 73.3% at 4 μg/ml) enzymes; 63.3% of P. aeruginosa were inhibited at the FDA's 1 μg/ml breakpoint. Lastly, cefiderocol 2 and 4 μg/ml inhibited 80.8% and 88.9% of the A. baumannii isolates respectively, with rates >85% for isolates with OXA-51-like, -23, -24, or -58 enzymes and 50% at 2 μg/ml and 80% at 4 μg/ml for those with NDM carbapenemases. Dipicolinic acid and avibactam weakly potentiated cefiderocol against Enterobacterales with MBLs and serine carbapenemase respectively, indicating incomplete β-lactamase stability

    Observing the products of stellar evolution in the old open cluster M67 with APOGEE

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    © 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society Recent works have shown how the [C/N] ratio in stars after the first dredge-up (FDU) can be used as an age estimator in virtue of its dependence on stellar mass. For this purpose, precise predictions of the surface chemical composition before and after the mixing takes place in the convective envelope of subgiant stars are necessary. Stellar evolution models can provide us with such predictions, although a comparison with objects of known age is needed for calibration. Open clusters are excellent test cases, as they represent a single stellar population for which the age can be derived through, e.g. isochrone fitting. In this study, we present a detailed analysis of stars belonging to the well-known open cluster M67 observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey in the twelfth data release of the Sloan Digital Sky Survey and whose chemical properties were derived with the APOGEE Stellar Parameters and Chemical Abundances Pipeline. We find that the [C/N] abundance of subgiant branch stars is overestimated by ∼0.2 dex due to an offset in the determination of the [N/Fe] abundance. Stars on the red giant branch and red clump are shown not to be affected by this offset. We derive [C/N]FDU = −0.46 ± 0.03 dex, which poses a strong constraint on calibrations of [C/N]FDU as age indicator. We also do not find any clear signature of additional chemical mixing processes that set in after the red giant branch bump. The results obtained for M67 indicate the importance of conducting high-resolution spectroscopic studies of open clusters of different ages in order to establish an accurate age-dating method for field stars
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