Activity of Ertapenem (MK-0826) versus Enterobacteriaceae with Potent β-Lactamases

Ertapenem (MK-0826; L-749,345), a new carbapenem with a long serum half-life, was tested, in vitro, against β-lactamase-producing bacteria. The new compound had a MIC at which 90% of the isolates were inhibited of 0.06 μg/ml for extended-spectrum β-lactamase (ESBL)-producing klebsiellas, compared with 0.5 μg/ml for imipenem, 16 μg/ml for cefepime, and >128 μg/ml for ceftazidime and piperacillin-tazobactam. MICs of ertapenem for AmpC-derepressed mutant Enterobacteriaceae were 0.015 to 0.5 μg/ml, whereas imipenem MICs were 0.25 to 1 μg/ml and those of cefepime were 0.5 to 4 μg/ml, and resistance to ceftazidime and piperacillin-tazobactam was generalized. Despite this good activity, the MICs of ertapenem for ESBL-positive klebsiellas mostly were two- to fourfold above those for ESBL-negative strains, and the MICs for AmpC-hyperproducing Enterobacter cloacae and Citrobacter freundii mutants exceeded those for the corresponding AmpC-basal mutants. These differentials did not increase when the inoculum was raised from 10(4) to 10(6) CFU/spot, contraindicating significant lability. Carbapenemase producers were also tested. The IMP-1 metallo-β-lactamase conferred substantial ertapenem resistance (MIC, 128 μg/ml) in a porin-deficient Klebsiella pneumoniae strain, whereas a MIC of 6 μg/ml was recorded for its porin-expressing revertant. SME-1 carbapenemase was associated with an ertapenem MIC of 2 μg/ml for Serratia marcescens S6, compared with <0.03 μg/ml for Serratia strains lacking this enzyme. In summary, ertapenem had good activity against strains with potent β-lactamases, except for those with known carbapenemases

Silver nanoparticles supported on passivated silica: Preparation and catalytic performance in alkyne semi-hydrogenation

Herein, we report the preparation of small and narrowly distributed (2.1 ± 0.5 nm) Ag nanoparticles supported on passivated silica, where the surface OH groups are replaced by OSiMe3 functionalities. This synthetic method involves the grafting of silver(i) bis(trimethylsilyl)amide ([AgN(SiMe3)2]4) on silica partially dehydroxylated at 700 °C, followed by a thermal treatment of the grafted complex under H2. The catalytic performance of this material was investigated in the semi-hydrogenation of propyne and 1-hexyne and compared with that of 2.0 ± 0.3 nm Ag nanoparticles supported on silica. Whilst surface passivation slightly decreases the activity in both reactions (by a factor 2–3), probably as a result of the decreased alkyne adsorption properties or the presence of less accessible active sites on the passivated support, the AgNP@SiO2 catalysts demonstrate a remarkable selectivity for the production of alkenes. © 2014 The Partner Organisations

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Structural differences between Sb- and Nb-doped tin oxides and consequences for electrical conductivity

Sb- and Nb-doped tin oxides have been prepared by a co-precipitation method. Whilst X-ray powder diffraction and EDX mapping indicate similar dopant distributions, more detailed characterisation by variable high-temperature XRD, 119Sn MAS NMR and Nb K-edge X-ray absorption near edge structure spectroscopy reveal clear differences in the oxide structures. This detailed structural information is used to validate the measured differences in electrical conductivity.ISSN:1144-0546ISSN:0398-9836ISSN:1369-926