Initial adhesion of Listeria monocytogenes to solid surfaces under liquid flow

Some strains of the food borne pathogen Listeria monocytogenes persist in food processing environments. The exact reason behind this phenomenon is not known, but strain differences in the ability to adhere to solid surfaces could offer an explanation. In the present work, initial adhesion of nine strains of L. monocytogenes was investigated under liquid flow at two levels of shear stress on six different surfaces using a flow chamber set-up with microscopy measurements. The surfaces tested were glass and PVC, and glass coated with beef extract, casein, and homogenised and unhomogenised milk. In addition, the effect of prior environmental stress (5% NaCl, low nutrient availability) on initial adhesion was investigated. The hydrophobicity of the investigated surfaces was determined by contact angle measurements and the surface properties of the investigated L. monocytogenes strains were determined using Microbial Adhesion To Solvents (MATS). All surfaces with the exception of PVC were found to be hydrophilic. Strain differences were found to significantly influence the initial adhesion rate (IAR) of all nine strains to all the surfaces (p < 0.05) at both low and high shear stress. Furthermore, there was a significant effect of the surfaces tested (p < 0.05) in the adhesion ability of almost all strains. The IAR was affected by flow rate (shear stress) as seen by a decrease in adhesion at high shear stress for most strains. A significant effect of interactions between strain-surface and strain-shear stress (p < 0.001) was observed but not of interactions between surface-shear stress. No correlation between surface hydrophobicity and IAR was observed. Addition of 5% NaCl during propagation resulted in a decrease in IAR whilst propagation in low nutrient media caused an increase indicating a general change in surface characteristics under these conditions. Known persisting strains did not display general better adherence.     

Uptake of divalent ions (Mn+2 and Ca+2) by heat-set whey protein gels

Divalent salts are used commonly for gelation of polymer molecules. Calcium, Ca(+2), is one of the most common divalent ions that is used in whey protein gels. Manganese, Mn(+2), is also divalent, but paramagnetic, enhancing relaxation decay rates in magnetic resonance imaging (MRI) and can be used as a probe to understand the behavior of Ca(+2) in whey protein gels. The objective of this study was to investigate the diffusion of Ca(+2) and Mn(+2) ions in heat-set whey protein gels by using MRI and nuclear magnetic resonance (NMR) relaxometry. Whey protein gels were immersed in solutions containing MnCl(2) and CaCl(2) at neutral pH. Images obtained with gels immersed in MnCl(2) solution revealed a relaxation sink region in the gel's surface and the thickness of the region increased with time. These "no signal" regions in the MR images were attributed to uptake of Mn(+2) by the gel. Results obtained with CaCl(2) solution indicated that since Ca(+2) did not have the paramagnetic effect, the regions where Ca(+2) diffused into the gel exhibited a slight decrease in signal intensity. The relaxation spectrums exhibited 3 populations of protons, for gels immersed in MnCl(2) solution, and 2 populations for gels in CaCl(2) solution. No significant change in T(2) distributions was observed for the gels immersed in CaCl(2) solution. The results demonstrated that MRI and NMR relaxometry can be used to understand the diffusion of ions into the whey protein gel, which is useful for designing gels of different physical properties for controlled release applications. PRACTICAL APPLICATION: Design of food systems for delivery of bioactive compounds requires knowledge of diffusion rates and structure. Utilizing magnetic resonance imaging the diffusion rates of ions can be measured. Relaxation spectra could yield information concerning molecular interactions.     

Anti-inflammatory and anti-hyperalgesic evaluation of the condiment laurel (Litsea guatemalensis Mez.) and its chemical composition

Litsea guatemalensis Mez., a native plant of Mexico and Central America, is widely used as a food condiment, in the same manner as Laurus nobilis L. In folk medicine, it is used to treat several diseases such as respiratory and gastrointestinal complaints. We report here the anti-inflammatory and anti-hyperalgesic properties of ethanolic extract and the compound 5,7,3′,4′-tetrahydroxy-isoflavone (3), which was isolated in addition to pinocembrin (1), and scopoletin (2). The results confirm that both the ethanolic extract and Compound 3 showed anti-inflammatory activity, by inhibiting paw oedema induced by carrageenan, and also reduced the influx of leucocytes, particularly neutrophils, to the pleural cavity and consequently anti-hyperalgesic activity, when assessed in the model of persistent pain induced by partial sciatic nerve ligation.     

The effect of the glass transition temperature on the toughness of photopolymerizable (meth)acrylate networks under physiological conditions

The purpose of this study is to evaluate how the toughness of photopolymerizable (meth)acrylate networks is influenced by physiological conditions. By utilizing two ternary (meth)acrylate networks, MA-co-MMA-co-PEGDMA and 2HEMA-co-BMA-co-PEGDMA, relationships between glass transition temperature (T_g), water content and state, and toughness were studied by varying the weight ratio of the linear monomers (MA to MMA or 2HEMA to BMA). Differential scanning calorimetry and thermogravimetric analysis were performed to evaluate the thermal behavior and water content as a function of either MA or 2HEMA concentration while tensile strain-to-failure tests were performed at 37 °C to determine network toughness. Both networks exhibited a maximum in toughness in PBS in the composition corresponding to a T_g close to the testing temperature. This toughness maximum was achieved by adjusting the glass transition temperature and/or hydrophilicity through changes in chemistry. These relationships may be utilized to design tough photopolymerizable networks for use in mechanically rigorous biomedical applications.     

Dynamic Frontier-Led Swarming: Multi-Robot Repeated Coverage in Dynamic Environments

A common assumption of coverage path planning research is a static environment.Such environments require only a single visit to each area to achieve coverage.However,some real-world environments are characterised by the presence of unexpected,dynamic obstacles.They require areas to be revisited periodically to maintain an accurate coverage map,as well as reactive obstacle avoidance.This paper proposes a novel swarmbased control algorithm for multi-robot exploration and repeated coverage in envir...     

Ultrasonic tracking of acoustic radiation force-induced displacements in homogeneous media

The use of ultrasonic methods to track the tissue deformation generated by acoustic radiation force is subject to jitter and displacement underestimation errors, with displacement underestimation being primarily caused by lateral and elevation shearing within the point spread function (PSF) of the ultrasonic beam. Models have been developed using finite element methods and Field II, a linear acoustic field simulation package, to study the impact of focal configuration, tracking frequency, and material properties on the accuracy of ultrasonically tracking the tissue deformation generated by acoustic radiation force excitations. These models demonstrate that lateral and elevation shearing underneath the PSF of the tracking beam leads to displacement underestimation in the focal zone. Displacement underestimation can be reduced by using tracking beams that are narrower than the spatial extent of the displacement fields. Displacement underestimation and jitter decrease with time after excitation as shear wave propagation away from the region of excitation reduces shearing in the lateral and elevation dimensions. The use of higher tracking frequencies in broadband transducers, along with 2D focusing in the elevation dimension, will reduce jitter and improve displacement tracking accuracy. Relative displacement underestimation remains constant as a function of applied force, whereas jitter increases with applied force. Underdeveloped speckle (SNR < 1.91) leads to greater levels of jitter and peak displacement underestimation. Axial shearing is minimal over the tracking kernel lengths used in acoustic radiation force impulse imaging and thus does not impact displacement tracking.     

Formation of metallic copper nanoparticles at the soil-root interface

Copper is an essential element in the cellular electron-transport chain, but as a free ion it can catalyze production of damaging radicals. Thus, all life forms attempt to prevent copper toxicity. Plants diminish excess copper in two structural regions: rare hyperaccumulators bind cationic copper to organic ligands in subaerial tissues, whereas widespread metal-tolerant plants segregate copper dominantly in roots by mechanisms thought to be analogous. Here we show using synchrotron microanalyses that common wetlands plants Phragmites australis and Iris pseudoacorus can transform copper into metallic nanoparticles in and near roots with evidence of assistance by endomycorrhizal fungi when grown in contaminated soil in the natural environment. Biomolecular responses to oxidative stress, similar to reactions used to abiotically synthesize Cu0 nanostructures of controlled size and shape, likely cause the transformation. This newly identified mode of copper biomineralization by plant roots under copper stress may be common in oxygenated environments.     

Stress, maternal distress, and children's adjustment following immigration: The buffering role of social support.

This study examined, in the context of a stress-buffering model, the relationship of certain family level variables to children's adjustment after immigration. Immigrant Chinese mothers from Hong Kong completed questionnaires regarding postmigration stress, personal distress, perceived social support, and their child's adjustment. Another adult also provided child behavior ratings. Analyses revealed that, for boys, family stress and maternal distress were significant predictors of child problems and that maternal support buffered the association between family stress and child problems. Contrary to expectation, the relationship between maternal distress and boys' problems was stronger at higher levels of maternal support. For families of girls, although there were significant relationships between the predictors and child behavior, no stress buffering was evident. Cultural explanations are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Taxonomy, assessment, and diagnosis of depression during adolescence.

Research on depressive phenomena during adolescence has focused on 3 separate constructs: depressed mood, depressive syndromes, and depressive disorders. Approaches to the assessment, taxonomy, and diagnosis of these 3 conceptualizations are reviewed. Each of the approaches is represented by different assessment tools measuring related but distinct aspects of depressive phenomena. The constructs share a common set of symptoms reflecting negative affectivity but differ in their inclusion of symptoms of anxiety, somatic problems, and disrupted concentration and in the duration and severity of the symptoms they include. Depressed mood, syndromes, and disorders are integrated as 3 levels of depressive phenomena in a hierarchical and sequential model, and moderating factors are hypothesized to account for the relationships among the 3 levels. The need for a stronger developmental focus to understand depressive phenomena during adolescence is emphasized. (PsycINFO Database Record (c) 2010 APA, all rights reserved)