Characterization of two bacteriocins produced by Pediococcus acidilactici isolated from "Alheira", a fermented sausage traditionally produced in Portugal

Lactic acid bacteria were isolated from "Alheira" sausages that have been sampled from different regions in Portugal. The sausages were produced according to different recipes and with traditional starter cultures. Two isolates (HA-6111-2 and HA-5692-3) from different sausages were identified as strains of Pediococcus acidilactici. Each strain produces a bacteriocin, designated as bacHA-6111-2 and bacHA-5692-3. Both bacteriocins are produced at low levels after 18 h of growth in MRS broth (3200 AU/ml against Enterococcus faecium HKLHS and 1600 AU/ml against Listeria innocua N27). BacHA-6111-2 and bacHA-5692-3 are between 3.5 kDa and 6.5 kDa in size, as determined by tricine-SDS-PAGE. Complete inactivation or significant reduction in antimicrobial activity was observed after treatment of cell-free supernatants with proteinase K, pronase and trypsin. No change in activity was recorded when treated with catalase. Both bacteriocins are sensitive to treatment with Triton X-114 and Triton X-100, but resistant to Tween 20, Tween 80, SDS, Oxbile, NaCl, urea and EDTA. The bacteriocins remained stable after 2 h at pH 6.0. A decrease in antibacterial activity was recorded after 60 min at 100 degrees C. After 60 min at 80 degrees C, 60 degrees C and 25 degrees C the antibacterial activity against L. innocua N27 decreased by 25%. Addition of bacHA-6111-2 and bacHA-5692-3 (1600 AU/ml) to a mid-log (5-h-old) culture of L. innocua N27 inhibited growth for 7 h. Addition of the bacteriocins (3200 AU/ml) to a mid-log (5-h-old) culture of E. faecium HKLHS repressed cell growth. The bacteriocins did not adhere to the surface of the producer cells. Both strains contain a 1044 bp DNA fragment corresponding in size to that recorded for pediocin PA-1. Sequencing of the fragments from both bacteriocins revealed homology to large sections of pedA (188 bp), pedB (338 bp) and pedC (524 bp) of pediocin PA-1 and the bacteriocins are considered similar to pediocin PA-1.     

Partial Characterization of Nine Bacteriocins Produced by Lactic Acid Bacteria Isolated from Cold-Smoked Salmon with Activity against Listeria monocytogenes

Nine LAB bacteriocin-producers, isolated from vacuum-packaged cold-smoked salmon (CSS), were phenotypically and genotypically identified as Lactobacillus curvatus, Lactobacillus delbrueckii, Lactobacillus fermentum, Enterococcus faecium, and Pediococcus acidilactici. Their bacteriocins were partially characterized. The antimicrobial spectrum was determined against Listeria monocytogenes, E. faecalis, E. faecium, and Staphylococcus aureus. The molecular size of bacteriocins ranged from 2.8 to 4.5 kDa. They were inactivated by treatment with proteolytic enzymes but not by lipolytic or glycolytic enzymes. Maximal activity against L. monocytogenes ranged between 800 and 10000 AU/mL at pH 6.5. Most of the bacteriocins maintained full activity in a pH range of 2.0 to 8.0 but were partially or completely inactivated at pH 10.0. After heating at 60°C and 100°C, only two bacteriocins from Lb. curvatus strains partially lost activity. All bacteriocins showed a narrow spectrum of activity and a high anti-listerial activity, which is characteristic of the class IIa bacteriocins. Isolated bacteriocin-producing LAB could be used successfully in the bio-preservation of CSS and development of new potential bio-preservatives for CSS active against L. monocytogenes.     

Numerical simulation of multi-species biofilms in porous media for different kinetics

There are bacteria that can form strong biofilms in porous media. These biofilms can be used as biobarriers to restrict the flow of pollutants. For certain contaminants, a second species of bacteria that can actually react with the contaminants can be added to the biobarrier to actually degrade the pollutants. We propose some mathematical models for the formation of these reacting biobarriers under different hypotheses, and numerically solve the resulting equations for the flow, transport and reactions. Qualitative comparisons with some experimental results are also given.     

Electrochemical PCT isotherm study of hydrogen absorption/desorption in AB5 type intermetallic compounds

The enthalpy (ΔH) and entropy (ΔS) of hydride formation/decomposition could be determined either experimentally or theoretically based on models proposed in the literature. The experimental pathway includes gas/solid-phase measurement of pressure–composition–temperature (PCT) isotherms at different temperatures. This measurement is followed by plotting of van't Hoff dependences and evaluation of the ΔH and ΔS from their slopes and intersects, respectively. In this study we demonstrate the applicability of electrochemical PCT isotherm measurements as an advanced method for thermodynamic analysis of hydrogen adsorption/desorption process. Experimentally this is done by electrochemical charging/discharging of an electrode, prepared from AB₅ type alloy with MmNi_4.6Co_0.6Al_0.8 composition (Mm – mischmetal). In addition, the hydride formation as a result of the electrochemical charging is independently confirmed by ex-situ XRD diffraction. Our work demonstrates that not only the electrochemical approach is a viable alternative of PCT gas/solid-phase measurement but it also represents a safer, cost-effective and faster protocol than its hydrogen gas–solid phase equivalent.     

Oxydation von α-Methylstyren in Gegenwart von Übergangsmetallverbindungen

Oxidation of α-Methylstyrene in the Presence of Transition Metal Compounds The kinetics of oxygen absorption by α-methylstyrene has been investigated under normal pressure at 60°C in the presence of Mo-, Mn-, Co-, Ir-, Rh and Pt-compounds. Under these conditions only compounds of Co and Mo accelerated the reaction considerably. From the results, which were obtained by addition of AIBN, CHP or PPMS and ionol respectively, it can be concluded that the main course of the oxidation is a radical chain mechanism. The effect of the metal complex does not result from an interaction with the polyperoxide. Furthermore there were indications that in the initial phase of the reaction a direct activation and transfer of oxygen might also take place.     

Interlaminar Stress Determination in Carbon Fibre Epoxy Composites with the Embedded Strain Gauge Technique

Abstract: In order to determine interlaminar stresses, strain gauges have been embedded in carbon fibre/epoxy composites. Insulation problems occurring because of the electrical conductivity of the carbon fibres were successfully resolved with the help of special foils. Measurements on unidirectional and angle‐ply laminates were in good agreement with calculations based on the classical laminate theory. Moreover, the laminate strength was not significantly affected by the embedded strain gauges. The technique may also be applied to residual stress determination in composite components.     

A Müller-Stokes Study of Polarization-mode Transformation in Randomly Perturbed Optical Fibres

Abstract

On the basis of Müller-Stokes marices for a uniformly perturbed fibre and the mode-coupling centre model polarization-mode transformation along randomly perturbed optical fibres has been studied. The process of spectral averaging in the quasimonochromatic case has been theoretically modelled and a computer simulation has been performed. The equivalent mode-coupling centre model has been applied to study the z-dependence of the polarization dispersion and the relationship between the degree of polarization, the polarization holding parameter and the coherence length in a single-mode fibre.     

Dependence of the textural properties and surface species of ZnO photocatalytic materials on the type of precipitating agent used in the hydrothermal synthesis

Three different precipitating agents (NaOH, \(\hbox {NH}_{4}(\hbox {H})\hbox {CO}_{3}\) and \(\hbox {CO}(\hbox {NH}_{2})_{2}\)) have been applied for the hydrothermal synthesis of ZnO powder materials, aiming at obtaining various types of porosity and surface species on ZnO. The synthesis procedures were carried out in the presence and in the absence of tri-block copolymer Pluronic (P123, EO20PO70EO20). These materials were characterized by powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM)–energy-dispersive X-ray spectroscopy (EDX), BET method and TG–differential thermal analysis (DTA) method, and their photocatalytic activities were tested in the removal azo dye Reactive Black 5 (RB5). The urea precipitant yields spongy-like surface forms and the greatest share of mesopores. It has the highest specific surface area, highest degree of crystallinity of wurtzite ZnO phase and largest content of surface OH groups in comparison with the other two precipitants. The zinc hydroxycarbonate intermediate phase is missing in the case of NaOH as precipitating agent; therefore, it manifests poorer textural characteristics. The morphology of P123-modified sample is different and consists of needle-shaped particles. The urea-precipitated samples display superior performance in the photocatalytic oxidation reaction, compared with the other precipitated samples. The other two precipitating agents are inferior in regard to their photocatalytic activity due to greater share of micropores (not well-illuminated inner surface) and different surface morphologies.     

Adjusted Rasch person-fit statistics

Two frequently used parametric statistics of person-fit with the dichotomous Rasch model (RM) are adjusted and compared to each other and to their original counterparts in terms of power to detect aberrant response patterns in short tests (10, 20, and 30 items). Specifically, the cube root transformation of the mean square for the unweighted person-fit statistic, t, and the standardized likelihood-based person-fit statistic Z3 were adjusted by estimating the probability for correct item response through the use of symmetric functions in the dichotomous Rasch model. The results for simulated unidimensional Rasch data indicate that t and Z3 are consistently, yet not greatly, outperformed by their adjusted counterparts, denoted t* and Z3*, respectively. The four parametric statistics, t, Z3, t*, and Z3*, were also compared to a non-parametric statistic, HT, identified in recent research as outperforming numerous parametric and non-parametric person-fit statistics. The results show that HT substantially outperforms t, Z3, t*, and Z3* in detecting aberrant response patterns for 20-item and 30-item tests, but not for very short tests of 10 items. The detection power of t, Z3, t*, and Z3*, and HT at two specific levels of Type I error, .10 and .05 (i.e., up to 10% and 5% false alarm rate, respectively), is also reported.     

Ultrasound research scanner for real-time synthetic aperture data acquisition

Conventional ultrasound systems acquire ultrasound data sequentially one image line at a time. The architecture of these systems is therefore also sequential in nature and processes most of the data in a sequential pipeline. This often makes it difficult to implement radically different imaging strategies on the platforms and makes the scanners less accessible for research purposes. A system designed for imaging research flexibility is the prime concern. The possibility of sending out arbitrary signals and the storage of data from all transducer elements for 5 to 10 seconds allows clinical evaluation of synthetic aperture and 3D imaging. This paper describes a real-time system specifically designed for research purposes. The system can acquire multichannel data in real-time from multi-element ultrasound transducers, and can perform some real-time processing on the acquired data. The system is capable of performing real-time beamforming for conventional imaging methods using linear, phased, and convex arrays. Image acquisition modes can be intermixed, and this makes it possible to perform initial trials in a clinical environment with new imaging modalities for synthetic aperture imaging, 2D and 3D B-mode, and velocity imaging using advanced coded emissions. The system can be used with 128-element transducers and can excite 128 transducer elements and receive and sample data from 64 channels simultaneously at 40 MHz with 12-bit precision. Two-to-one multiplexing in receive can be used to cover 128 receive channels. Data can be beamformed in real time using the system's 80 signal processing units, or it can be stored directly in RAM. The system has 16 Gbytes RAM and can, thus, store more than 3.4 seconds of multichannel data. It is fully software programmable and its signal processing units can also be reconfigured under software control. The control of the system is done over a 100-Mbits/s Ethernet using C and Matlab. Programs for doing, e.g., B-mode imaging can be written directly in Matlab and executed on the system over the net from any workstation running Matlab. The overall system concept is presented along with its implementation and examples of B-mode and in vivo synthetic aperture flow imaging.