Dairy biofilm: Bacterial community diversity assessment and impact of the Lactococcus lactis bio adhesion on biofilm growth

Biofilms are the most common mode of bacterial growth in nature. Their formation occurs on organic or inorganic solid surfaces in contact with a liquid, on gas-liquid and liquid-liquid boundaries as well. The aims of this study were, by combining cell enumeration, scanning electron microscopy and denaturing gel gradient electrophoresis (DGGE), to characterize the structural dynamics of dairy biofilm growth in the environments with a nutrient flow, and to evaluate the impact of adhesion of Lactococcus lactis on the biofilm community depending on the incubation time. Significantly higher values of biofilm volume and thickness were observed under dynamic conditions after 55 h. The populations of gram-positive bacteria and fungi exhibited a significantly higher biofilm organization after 2 days of cultivation than that of gram-negative bacteria. Also, results showed that Lc. lactis was able to adhere to silicone surface and the produced biofilm in which the number of adhered gram-positive and gram-negative bacteria decreased by nine orders of magnitude after 48 h of contact. This study constitutes a step ahead in developing the strategies to prevent microbial colonization by lactococcal protective biofilm.     

Synthesis of novel 3-pyridinecarbonitriles with amino acid function and their fluorescence properties

Summary. A variety of N-[(4,6-diaryl-3-pyridinecarbonitrile)-2-yl] amino acid esters 2–4 were synthesized through the reaction of 2-bromo-3-pyridinecarbonitriles 1 with the appropriate -amino acid ester hydrochloride in refluxing dioxane in the presence of triethylamine as dehydrohalogenating agent. Similarly, N-glycylglycine analogues 5 were obtained through the reaction of 1 with the dipeptide ester. On the other hand, attempts were made towards the construction of amino acid derivatives 7 through the reaction of 1 with aqueous solution -amino acids 6 in refluxing pyridine, but were unsuccessful, and instead the unexpected 2-amino-3-pyridinecarbonitriles 8 were isolated. The fluorescence properties of the newly synthesized pyridines 2–5 were evaluated. Some of the prepared compounds show considerable antibacterial activity.     

Antioxidant activity of extract of Rhus oxyacantha root cortex

In the present study, the root extract of Rhus oxyacantha contained 25.33 mg of catechin equivalent per mg of fresh wt and was found rich in proanthocyanidins compared to vine shoot, grape pips and leaves. The chromatographic analysis of the extract suggested the presence of (+) catechin, (-) epicatechin -3-O-gallate as well as proanthocyanidinic oligomers and polymers. Root cortex inhibited the ascorbic acid oxidation by dioxygen. It also prevented DDT-induced thymocytes death in a dose-dependent manner. The results suggested antioxidant property of root extract of Rhus oxyacantha which could be ascribed to its free radical scavenging nature.     

Kinetic Modelling of <Emphasis Type="Italic">Lactobacillus casei</Emphasis> ssp. <Emphasis Type="Italic">rhamnosus</Emphasis> Growth and Lactic Acid Production in Batch Cultures Under Various Medium Conditions

Enrichment of medium with yeast extract and tryptone increased growth and lactic acid production in batch cultures of Lactobacillus casei ssp. rhamnosus. A reliable kinetic model that explicitly expresses the strong relationship between microbial growth, lactic acid production and medium enrichment is provided and validated using experimental data obtained with six different medium compositions. Revisions requested 2 February 2005 and 26 July 2005; Revisions received 25 July 2005 and 9 September 2005     

Ion Current Rectification,Limiting and Overlimiting Conductances in Nanopores

Previous reports on Poisson-Nernst-Planck (PNP) simulations of solid-state nanopores have focused on steady state behaviour under simplified boundary conditions. These are Neumann boundary conditions for the voltage at the pore walls, and in some cases also Donnan equilibrium boundary conditions for concentrations and voltages at both entrances of the nanopore. In this paper, we report time-dependent and steady state PNP simulations under less restrictive boundary conditions, including Neumann boundary conditions applied throughout the membrane relatively far away from the nanopore. We simulated ion currents through cylindrical and conical nanopores with several surface charge configurations, studying the spatial and temporal dependence of the currents contributed by each ion species. This revealed that, due to slow co-diffusion of oppositely charged ions, steady state is generally not reached in simulations or in practice. Furthermore, it is shown that ion concentration polarization is responsible for the observed limiting conductances and ion current rectification in nanopores with asymmetric surface charges or shapes. Hence, after more than a decade of collective research attempting to understand the nature of ion current rectification in solid-state nanopores, a relatively intuitive model is retrieved. Moreover, we measured and simulated current-voltage characteristics of rectifying silicon nitride nanopores presenting overlimiting conductances. The similarity between measurement and simulation shows that overlimiting conductances can result from the increased conductance of the electric double-layer at the membrane surface at the depletion side due to voltage-induced polarization charges. The MATLAB source code of the simulation software is available via the website http://micr.vub.ac.be.     

FFED: a novel strategy based on fast entropy to detect attacks against trust computing in cloud

Cluster Computing - Trust management systems give way to trustworthy interactions in cloud computing. However, malicious cloud users can intentionally provide unfair ratings to benefit or reduce a...     

The impact of thyroid activity variations on some oxidizing-stress parameters in rats

The effect of the thyroid activity on the formation of lipid peroxidation and on liver and heart antioxidant enzyme activities was investigated in Wistar rats. Hypothyroidism and hyperthyroidism conditions were induced for five weeks by the administration of 0.05% benzythiouracile (BTU) and L-thyroxine sodium salt (0.0012%), in drinking water, respectively. No significant effect was observed on the rates of both lipid peroxidation and the vitamin E in hepatic and cardiac tissues of hypothyroidism rats compared to the controls, contrary to the hyperthyroidism rats, which expressed a pronounced increase. The increased glutathione peroxidase activity in rats suffering from hyperthyroidism was associated with a fall of the reduced glutathione in the homogenate and a marked increase in the glutathione reductase activity. An increase in superoxide dismutase and catalase activities was also recorded in hyperthyroidism. Our results explain the thyroid activity variation in relation to the lipid peroxidation and the tissular contents of the enzymatic and the non-enzymatic antioxidants. To conclude, our results show the occurrence of a state of oxidizing stress in relation to hyperthyroidism.     

Measurement of chlorine dioxide penetration in dairy process pipe biofilms during disinfection

Biofilms are considered a significant health risk in the food and dairy industries because they can harbor pathogens, and direct contact with them can lead to food contamination. Biofilm control is often performed using strong oxidizing agents like chlorine and peracetic acid. Although chlorine dioxide (ClO₂) is being used increasingly to control microbiological growth in a number of different industries, not much is known about disinfection in biofilms using chlorine dioxide. In this study, a microelectrode originally made for chlorine detection was modified to measure the profiles of chlorine dioxide in biofilm as a function of depth into the biofilm. In addition, discarded microelectrodes proved useful for in situ direct measurement of biofilm thicknesses. The chlorine dioxide microelectrode had a linear response when calibrated up to a ClO₂ concentration of 0.4 mM. ClO₂ profiles showed depletion of disinfectant at 100 μm in the biofilm depth, indicating that ClO₂ may not reach bacteria in a biofilm thicker than this using a 25 mg/l solution.     

Strategy for identification of Bacillus cereus and Bacillus thuringiensis strains closely related to Bacillus anthracis

Bacillus cereus strains that are genetically closely related to B. anthracis can display anthrax-like virulence traits (A. R. Hoffmaster et al., Proc. Natl. Acad. Sci. USA 101:8449-8454, 2004). Hence, approaches that rapidly identify these "near neighbors" are of great interest for the study of B. anthracis virulence mechanisms, as well as to prevent the use of such strains for B. anthracis-based bioweapon development. Here, a strategy is proposed for the identification of near neighbors of B. anthracis based on single nucleotide polymorphisms (SNP) in the 16S-23S rRNA intergenic spacer (ITS) containing tRNA genes, characteristic of B. anthracis. By using restriction site insertion-PCR (RSI-PCR) the presence of two SNP typical of B. anthracis was screened in 126 B. cereus group strains of different origin. Two B. cereus strains and one B. thuringiensis strain showed RSI-PCR profiles identical to that of B. anthracis. The sequencing of the entire ITS containing tRNA genes revealed two of the strains to be identical to B. anthracis. The strict relationship with B. anthracis was confirmed by multilocus sequence typing (MLST) of four other independent loci: cerA, plcR, AC-390, and SG-749. The relationship to B. anthracis of the three strains described by MLST was comparable and even higher to that of four B. cereus strains associated with periodontitis in humans and previously reported as the closest known strains to B. anthracis. SNP in ITS containing tRNA genes combined with RSI-PCR provide a very efficient tool for the identification of strains closely related to B. anthracis.     

Molecular characterization and phylogenetic comparisons of three <Emphasis Type="Italic">Mayetiola</Emphasis> species (Diptera: Cecidomyiidae) infesting cereals in Tunisia

Species from the genus Mayetiola are observed in the main cereal cultures of Tunisia. Some researchers have studied M. destructor that attacks wheat and M. hordei that attacks barley. However, a third important species observed in oat, M. avenae, has not been studied and is not well documented in Tunisia. A method to easily separate the species is needed to clarify the occurrences of these gall midge species. This study aimed to first distinguish between the three species of gall midges by molecular characterization and second to reveal the phylogenetic relationships within and between the three species of Mayetiola collected from 5 different regions of northern Tunisia. To achieve these purposes, two regions of the mitochondrial DNA, cytochrome oxidase subunit I gene, and the 16S rRNA gene were amplified by polymerase chain reaction and sequenced. For each marker, a set of 75 individuals were used for DNA analysis. Phylogenetic trees were created using the DNA sequences of all samples from the 3 species. Results showed significant separation of the three different species into dissimilar clades. Each clade contained only specimens from the same species. Differences were observed between DNA sequences of the same species. The differences within the same species were not representative of geographical variations but coexisted within a population Therefore, using the COI and 16S rRNA genes as markers can clearly separate M. avenae, M. destructor and M. hordei.