Influence of autoinducer-2 (AI-2) and beef sample extracts on E. coli O157:H7 survival and gene expression of virulence genes yadK and hhA

ABSTRACT:  Bacterial cell-to-cell communication is mediated by autoinducer (AI) molecules such as AI-2 and has been reported to regulate gene expression in Escherichia coli O157:H7. We have previously shown that ground beef contains compounds that can inhibit sensing of AI-2 like activity. The hypothesis of this study was that AI-2 activity observed in conditioned medium (CM) will enhance E. coli O157:H7 survival and expression of virulence genes, whereas compounds inhibitory (such as those present in ground beef extracts) to AI-2 activity will negate these effects. E. coli O157:H7 luxS mutant strain VS 94 (incapable of synthesizing AI-2) was employed in these studies. The survival of this enteric bacterial pathogen as a function of AI-2 activity and the presence of AI-2 inhibitory compounds was studied at 4 °C. The number of survivors in the presence of AI-2 was significantly higher compared to the absence of AI-2, and the addition of ground beef extracts to conditioned medium negated the influence of AI-2 activity. Autoinducer AI-2 upregulated selected genes virulence genes ( yadK , and hha ), whereas the ground beef extract reversed the effect of AI-2 on the expression of the selected genes.     

Immobilization of papain on crosslinked polymer supports: Role of the macromolecular matrix on enzymic activity

Papain was immobilized on polymer supports with spacer arms of varying nature and length. As the length of the spacer arm increased, there was a marked increase in the extent of enzyme immobilization and activity of immobilized enzymes. When a long, flexible and hydrophilic polyethylene glycol spacer was introduced between the polystyrene backbone and the functional group used for immobilization, the extent of coupling and enzyme activity increased. Dependence of enzyme activity on the nature and extent of crosslinking and on the nature of the polymeric backbone was investigated. Hydrophilic polyacrylamide-based supports were found to be more efficient supports for immobilization compared to hydrophobic polystyrene-based supports.     

Persistent internal polarization studies in poly(N-vinylcarbazole)trinitrofluorenone charge transfer complex

Studies on the persistent internal polarization in poly(N-vinylcarbazole) (PNVC)/trinitrofluorenone (TNF) charge transfer complex are reported. This complex is known to be photoconducting and in the present investigation, the photoelectret charge has been studied as a function of applied voltage, intensity of illumination and time of polarization. A saturation effect is observed in each case. Also the possibility of the use of PNVC/TNF complex in PIP electrophotography has been explored and a comparison of the results of this investigation is made with the results obtained for PNVC.     

Practical calculation of switching surges at motor terminals

Switching of motors results in steep-fronted surges which cause a relatively large turn-to-turn stress in windings. Simplified and detailed methods are presented for calculating the surge level and risetime at the motor terminals for particular configurations. The levels are shown to be strongly affected by shield or conduit grounding practices and are less dependent on motor size or the number of other loads supplied by the metal-clad bus. The risetimes depend mainly on the motor cable impedance, the shield grounding practices, and an equivalent motor capacitance. Less sensitive parameters include metal-clad bus length, the breaker position, and cable losses associated with the dielectric, skin effect, and semiconductive layers. Comparisons are made with surges monitored during normal switching     

Kalman–Yakubovich lemma in the behavioural setting

In this paper, the Kalman–Yakubovich lemma is formulated and proved in the behavioural theoretic setting. The behavioural framework is used to generalize the lemma, for behaviours with two manifest variables, with respect to supply rates that are quadratic differential forms (QDFs).     

Study and Analysis of the Effect of Harmonics on the Hot Spot Temperature of a Distribution Transformer Using Finite-Volume Method

Transformers are critical components in power systems and their failure can cause long interruption of power supply. The condition of a transformer can be monitored by performing thermal analysis. The use of non-linear devices, such as rectifiers and converters, draws harmonic currents that increase losses in transformers, thereby increasing their operating temperature. In this article, a new numerical approach is presented for determining the rise in hot spot temperature in a 5-kVA, 400/400-V dry-type three-phase transformer laboratory prototype. The key novelty is that the additional winding eddy current loss due to non-linear loads is considered in the numerical modeling. The winding eddy current loss corresponding to harmonic distortion is estimated by conducting experiments and calculations. Numerical simulations are carried out for a wide range of non-linear loads using a commercial computational fluid dynamics package, FLUENT 6.3. The proposed numerical methodology is validated by performing experiments on the transformer for possible non-linear loads and comparing the measured hot spot temperature with the simulated values. Correlation equations for rise in hot spot temperature as a function of total harmonic distortion are presented, which can be used for estimating the life of transformers when connected to different types of loads.     

Near infrared light-induced disassembly of polymeric micelles based on methylene blue conjugated polyethylene glycol

Light-sensitive drug delivery systems are considered ideal for applications in the biomedical fields for their ability to release the payload in an on-demand spatiotemporal controlled manner through the manipulation of the light source. Among the broad radiation spectrum, near infrared (NIR) light is considered advantageous compared to UV and visible light, due to its inherently lower photodamage to normal tissues and deeper penetration to lesion areas. In this study, we report a successful synthesis of a polymer capable of undergoing partial degradation upon irradiation with NIR light by conjugating 10-N-carbamoyl linkage methylene blue (MB) moiety, a NIR photocleavable ligand, with polyethylene glycol (PEG). Through effective coupling of MB, a hydrophobic moiety, to the hydrophilic PEG molecule, an amphiphilic polymer was synthesized, as demonstrated by a lowered surface tension (55 mN/m at 0.1% wt/vol). Subsequently, photo-induced reversal of surface activity associated with self-assembled structure disruption, was displayed by surface tension measurements, size distribution analysis, and burst release profile of paclitaxel (PTX) from polymeric micelles upon the exposure to NIR irradiation.     

Compression based clustering technique for enhancing accuracy in web scale videos

Multimedia Tools and Applications - Detection and clustering of commercial advertisements plays an important role in multimedia indexing also in the creation of personalized user content. In...     

Homology modeling of the DNA-binding domain of human Smad5: a molecular model for inhibitor design

Members of the Smad protein family function as signal transducers of the transforming growth factor (TGF-beta) superfamily proteins. The human Smad5 protein, a signal transducer downstream of TGF-beta/BMP receptors, is composed of N-terminal DNA binding domain (MH1) and C-terminal protein-protein interaction domain (MH2) connected together by a linker motif. We used homology-modeling techniques to generate a reliable molecular model of the Smad5 MH1 domain based on the crystal structure of Smad3 MH1 domain. Our study presents the structural features of a BMP-regulated, R-Smad subfamily member (consisting of Smad1, Smad5 and Smad8) for the first time. This model provides a structural basis for explaining both functional similarities and differences between Smad3 and Smad5. Also, the structural model of this molecular target would be useful for structure-based inhibitor design because of its high accuracy. The results of our study provide important insights into understanding the structure-function relationship of the members of the Smad protein family and can serve to guide future genetic and biochemical experiments in this area.