101 research outputs found
α,α-disubstituted β-amino amides eliminate Staphylococcus aureus biofilms by membrane disruption and biomass removal
Bacterial biofilms account for up to 80% of all infections and complicate successful therapies due to their intrinsic tolerance to antibiotics. Biofilms also cause serious problems in the industrial sectors, for instance due to the deterioration of metals or microbial contamination of products. Efforts are put in finding novel strategies in both avoiding and fighting biofilms. Biofilm control is achieved by killing and/or removing biofilm or preventing transition to the biofilm lifestyle. Previous research reported on the anti-biofilm potency of α,α-disubstituted β-amino amides A1, A2 and A3, which are small antimicrobial peptidomimetics with a molecular weight below 500 Dalton. In the current study it was investigated if these derivatives cause a fast disintegration of biofilm bacteria and removal of Staphylococcus aureus biofilms. One hour incubation of biofilms with all three derivatives resulted in reduced metabolic activity and membrane permeabilization in S. aureus (ATCC 25923) biofilms. Bactericidal properties of these derivatives were attributed to a direct effect on membranes of biofilm bacteria. The green fluorescence protein expressing Staphylococcus aureus strain AH2547 was cultivated in a CDC biofilm reactor and utilized for disinfectant efficacy testing of A3, following the single-tube method (American Society for Testing and Materials designation number E2871). A3 at a concentration of 90 μM acted as fast as 100 μM chlorhexidine and was equally effective. Confocal laser scanning microscopy studies showed that chlorhexidine treatment lead to fluorescence fading indicating membrane permeabilization but did not cause biomass removal. In contrast, A3 treatment caused a simultaneous biofilm fluorescence loss and biomass removal. These dual anti-biofilm properties make α,α-disubstituted β-amino amides promising scaffolds in finding new control strategies against recalcitrant biofilms
Single-Electron Electronics
Contains table of contents for Section 2, research goals and objectives, a summary of recent work and a list of publications.Joint Services Electronics Program Contract DAAHO4-95-1-0038U.S. Army Research Office Grant DAAHO4-94-G-011
Interference in interacting quantum dots with spin
We study spectral and transport properties of interacting quantum dots with
spin. Two particular model systems are investigated: Lateral multilevel and two
parallel quantum dots. In both cases different paths through the system can
give rise to interference. We demonstrate that this strengthens the multilevel
Kondo effect for which a simple two-stage mechanism is proposed. In parallel
dots we show under which conditions the peak of an interference-induced orbital
Kondo effect can be split.Comment: 8 pages, 8 figure
Minimum information guideline for spectrophotometric and fluorometric methods to assess biofilm formation in microplates
Supplementary data to this article can be found online at https://doi.org/10.1016/j.bioflm.2019.100010.The lack of reproducibility of published studies is one of the major issues facing the scientific community, and the field of biofilm microbiology has been no exception. One effective strategy against this multifaceted problem is the use of minimum information guidelines. This strategy provides a guide for authors and reviewers on the necessary information that a manuscript should include for the experiments in a study to be clearly interpreted and independently reproduced. As a result of several discussions between international groups working in the area of biofilms, we present a guideline for the spectrophotometric and fluorometric assessment of biofilm formation in microplates. This guideline has been divided into 5 main sections, each presenting a comprehensive set of recommendations. The intention of the minimum information guideline is to improve the quality of scientific communication that will augment interlaboratory reproducibility in biofilm microplate assays.This project has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska – Curie grant agreement No 722467, as part of the Print-Aid consortium.
The information and views set out in this article are those of the authors and do not necessarily reflect the official opinion of the European Union. Neither the European Union institutions and bodies nor any person
acting on their behalf may be held responsible for the use which may be made of the information contained therein.
This work received additional financial support by: project UID/EQU/00511/2019 - Laboratory for Process Engineering, Environment, Biotechnology and Energy – LEPABE funded by national funds through
FCT/MCTES (PIDDAC); Project “LEPABE-2-ECO-INNOVATION” – NORTE-01-0145-FEDER-000005, funded by Norte Portugal Regional Operational Programme (NORTE 2020), under PORTUGAL 2020 Partnership Agreement, through the European Regional Development Fund (ERDF).info:eu-repo/semantics/publishedVersio
Interlaboratory study for the evaluation of three microtiter plate-based biofilm quantification methods
Microtiter plate methods are commonly used for biofilm assessment. However, results obtained with these methods have often been difficult to reproduce. Hence, it is important to obtain a better understanding of the repeatability and reproducibility of these methods. An interlaboratory study was performed in five different laboratories to evaluate the reproducibility and responsiveness of three methods to quantify Staphylococcus aureus biofilm formation in 96-well microtiter plates: crystal violet, resazurin, and plate counts. An inter-lab protocol was developed for the study. The protocol was separated into three steps: biofilm growth, biofilm challenge, biofilm assessment. For control experiments participants performed the growth and assessment steps only. For treatment experiments, all three steps were performed and the efficacy of sodium hypochlorite (NaOCl) in killing S. aureus biofilms was evaluated. In control experiments, on the log(10)-scale, the reproducibility SD (S-R) was 0.44 for crystal violet, 0.53 for resazurin, and 0.92 for the plate counts. In the treatment experiments, plate counts had the best responsiveness to different levels of efficacy and also the best reproducibility with respect to responsiveness (Slope/S-R=1.02), making it the more reliable method to use in an antimicrobial efficacy test. This study showed that the microtiter plate is a versatile and easy-to-use biofilm reactor, which exhibits good repeatability and reproducibility for different types of assessment methods, as long as a suitable experimental design and statistical analysis is applied.Peer reviewe
The influence of binarity on dust obscuration events in the planetary nebula M 2-29 and its analogues
The central star of the planetary nebula (CSPN) M 2-29 shows an extraordinary
R Coronae Borealis-like fading event in its optical lightcurve. The only other
CSPN to show these events are CPD-568032 (Hen 3-1333) and V651 Mon (NGC 2346).
Dust cloud formation in the line of sight appears responsible but the exact
triggering mechanism is not well understood. Understanding how planetary
nebulae (PNe) trigger dust obscuration events may help understand the same
process in a wide range of objects including Population-I WC9 stars, symbiotic
stars and perhaps Asymptotic Giant Branch (AGB) stars with long secondary
periods (LSPs). A binary scenario involving an eccentric, wide companion that
triggers dust formation via interaction at periastron is a potential
explanation that has been suggested for LSP variables. Model fits to the
lightcurves of CPD-568032 and M 2-29 show the dust forms in excess of 70 AU at
the inner edge of a dust disk. In the case of CPD-568032 this radius is far too
large to coincide with a binary companion trigger, although a binary may have
been responsible for the formation of the dust disk. We find no direct evidence
to support previous claims of binarity in M 2-29 either from the OGLE
lightcurve or deep medium-resolution VLT FLAMES spectroscopy of the CSPN. We
classify the CSPN as Of(H) with T_eff=50+-10 kK and log g=4.0+-0.3. We find a
mean distance of 7.4+-1.8 kpc to M 2-29 at which the M_V=-0.9 mag CSPN could
potentially hide a subgiant luminosity or fainter companion. A companion would
help explain the multiple similarities with D'-type symbiotic stars whose outer
nebulae are thought to be bona-fide PNe. The 7.4 kpc distance, oxygen abundance
of 8.3 dex and Galactic coordinates (l=4.0, b=-3.0) prove that M 2-29 is a
Galactic Bulge PN and not a Halo PN as commonly misconceived.Comment: 15 pages, 14 figures, 7 tables. Accepted for publication in A\&
Infrared Space Observatory Spectra of R Coronae Borealis Stars. I. Emission Features in the Interval 3 - 25 microns
Infrared Space Observatory 3 - 25 m spectra of the R Coronae Borealis
stars V854 Cen, R CrB, and RY Sgr are presented and discussed. Sharp emission
features coincident in wavelengths with the well known Unidentified Emission
Features are present in the spectrum of V854 Cen but not of R CrB or RY Sgr.
Since V854 Cen is not particularly H-poor and has a 1000 times more H than the
other stars, the emission features are probably from a carrier containing
hydrogen. There is a correspondence between the features and emission from
laboratory samples of hydrogenated amorphous carbon. A search for C in
emission or absorption proved negative. Amorphous carbon particles account for
the broad emission features seen between 6 - 14 m in the spectrum of each
star.Comment: 11 pages with 2 tables and 4 figures in ApJ print page form. Accepted
for publication in Ap
Detection of an asymmetry in the envelope of the carbon Mira R Fornacis using VLTI/MIDI
Aims. We present a study of the envelope morphology of the carbon Mira R For
with VLTI/MIDI. This object is one of the few asymptotic giant branch (AGB)
stars that underwent a dust-obscuration event. The cause of such events is
still a matter of discussion. Several symmetric and asymmetric scenarios have
been suggested in the literature. Methods. Mid-infrared interferometric
observations were obtained separated by two years. The observations probe
different depths of the atmosphere and cover different pulsation phases. The
visibilities and the differential phases were interpreted using GEM-FIND, a
tool for fitting spectrally dispersed interferometric observations with the
help of wavelength-dependent geometric models. Results. We report the detection
of an asymmetric structure revealed through the MIDI differential phase. This
asymmetry is observed at the same baseline and position angle two years later.
The observations are best simulated with a model that includes a uniform-disc
plus a Gaussian envelope plus a point-source. The geometric model can reproduce
both the visibilities and the differential phase signatures. Conclusions. Our
MIDI data favour explanations of the R For obscuration event that are based on
an asymmetric geometry. We clearly detect a photocentre shift between the star
and the strongly resolved dust component. This might be caused by a dust clump
or a substellar companion. However, the available observations do not allow us
to distinguish between the two options. The finding has strong implications for
future studies of the geometry of the envelope of AGB stars: if this is a
binary, are all AGB stars that show an obscuration event binaries as well? Or
are we looking at asymmetric mass-loss processes (i.e. dusty clumps) in the
inner part of a carbon-rich Mira?Comment: accepted for publication as A&A lette
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