Assessment of different selective agar media for enumeration and isolation of Listeria from dairy products

Different selective agar media were compared for the recovery and isolation of five species of Listeria from raw milk and cheese. The selective media examined were Beerens medium, MacBride medium and that described by Dominguez et al. (1984) with 6 mg/l acriflavine, listeria selective agar medium (LSAM), and LSAM with 12 mg/l acriflavine (LSAM X 2A); a non-selective yeast glucose Lemco agar was included for comparison. When the difference between listeria and the natural microflora of raw milk and cheese was 10(2) cfu/ml, listeria could be isolated by direct plating on all media tested. When it was lower than 10(3)-10(4) cfu/ml, listeria were isolated by direct plating only on LSAM and LSAM X 2A. When the difference was greater than 10(4) cfu/ml, a previous enrichment was necessary to isolate them. LSAM and LSAM X 2A media performed better than the other media tested for isolating listeria by direct plating and improved their isolation from dairy products. This superior performance was evaluated by the ability of these media to support colony formation of different species of Listeria tested, the easy recognition of these colonies from those formed by other microorganisms and by their capacity to inhibit the natural microflora of these foods.     

Cellular proteins bind to multiple sites of the leader region of cauliflower mosaic virus 35S RNA

Recently, several studies have proposed models describing the mechanisms of Alzheimer's beta-amyloid fibril formation in vitro. However, these models are somewhat controversial and no exact kinetic analyses measuring the polymerization velocity as an indicator of the reaction, have thus far been available. We first formed beta-amyloid fibrils from a synthetic peptide, beta-amyloid(1-40), and determined the optimum conditions for quantitative fluorometry of these beta-amyloid fibrils with thioflavine T. Optimum fluorescence measurements of beta-amyloid fibrils were obtained at the excitation and emission wavelengths of 446 and 490 nm, respectively, with the reaction mixture containing 5 microM thioflavine T and 50 mM of glycine-NaOH buffer, pH 8.5. We then focused our study on the extension phase of beta-amyloid fibril formation in vitro. When beta-amyloid fibrils were incubated with monomeric beta-amyloid(1-40) in conditions where de novo seed formation does not occur, the extension of beta-amyloid fibrils was observed with electron microscopy. Quantitative fluorometry revealed that: (a) extension of amyloid fibrils proceeded by a pseudo-first-order exponential increase as measured by the fluorescence of thioflavine T; (b) the rate of extension was maximum around pH 7.5, and was dependent on the incubation temperature. Between 20 and 37 degrees C, good linearity was observed between the common logarithm of the initial rate and the reciprocal of the absolute temperature; (c) the rate of polymerization was found to be proportional to the product of beta-amyloid fibrils number concentration and the beta-amyloid(1-40) concentration; (d) the net rate of extension was the sum of the rates of polymerization and depolymerization. These results show that beta-amyloid fibril formation can be explained by a first-order kinetic model: i.e., the extension of beta-amyloid fibrils proceeds via the consecutive association of beta-amyloid(1-40) onto the ends of existing fibrils.     

The use of tooth thickness in predicting intermaxillary tooth-size discrepancies

Intermaxillary tooth-size discrepancies can be assessed using a diagnostic setup or predicted using a mathematical formula, such as the Bolton analysis. However, variations in tooth thickness may produce inaccuracies in the Bolton analysis ratio. To date, no method for incorporating tooth thickness into discrepancy prediction has been proposed. The purpose of this study was to design and test a new method of predicting anterior tooth-size discrepancy that takes into account tooth thickness and width. Forty-four positioner setup models were set to ideal overbite (2.5 mm) and occlusion (Class I canine relationship). Interproximal gaps between the maxillary or mandibular central incisors were allowed in order to optimize tip and torque. The mesiodistal width of all anterior teeth and the labiolingual thickness of the maxillary incisors were measured on these idealized setups to the nearest 0.1 mm. Actual intermaxillary anterior ratios were then calculated. A new method of prediction was developed by assuming a linear relationship between tooth thickness and ideal intermaxillary ratio. Errors in Bolton's method were compared with the new method. The results showed wide variations in mesiodistal tooth widths, tooth thicknesses, and intermaxillary anterior ratios in orthodontically treated patients. The correlation coefficient between the intermaxillary ratio and tooth thickness was r = 0.68 when tooth thickness was < 2.75 mm, and r = 0.28 when tooth thickness was > or = 2.75 mm. The mean absolute errors in predicting the actual intermaxillary ideal ratio was 1.29 +/- 0.81 for Bolton's ratio and 0.84 +/- 0.46 for the new prediction formula. These new formulas were better than Bolton's ratio in predicting tooth-size discrepancies (p = 0.003). Tooth thickness combined with mesiodistal width may be useful in predicting intermaxillary tooth-size discrepancies.     

The relationship between dental disease and cerebral vascular accident in elderly United States veterans

Enantiomers of N-methyl-N,alpha-methylbenzylbutyramide (1), 1-butyl-3-methyl-3'-alpha-methylbenzylurea (2), 1,2,3, 4-tetrahydro-1-naphthyl-N-butylcarbamate (3), 1,1'-bi-2-naphthyl-2, 2'-di-N-butylcarbamate (4), 1, 1'-bi-2-naphthyl-2-ol-2'-N-butylcarbamate (5), and 1, 1'-bi-2-naphthyl-2-butyrate-2'-N-butylcarbamate (6) are inhibitors of porcine pancreatic cholesterol esterase-catalyzed hydrolysis of 4-nitrophenyl butyrate and of electric eel acetylcholinesterase-catalyzed hydrolysis of acetylthiocholine in the presence of 5,5'-dithiobis-2-nitrobenzoate. For competitive inhibitors, values of the inhibition constant (Ki) and the enantiomeric ratio (Ecomp.) are investigated. For active site-directed irreversible inhibitors, values of the inhibition constant (Ki), the carbamylation constant (k2), the bimolecular rate constant (ki), and the enantiomeric ratio (E) are investigated. Toward both enzymes, compounds 1 are poor competitive inhibitors (Ki=102-104 microM) but have good enantioselectivities (Ecomp.=10-50, the preference for R). R-2 and S-2 are competitive inhibitors of acetylcholinesterase with Ki=26 and 80 microM, respectively (the preference for R) but are active site-directed irreversible inhibitors of cholesterol esterase with ki=4 and 16 M-1 sec-1, respectively (the preference for S). For those competitive inhibitions, both leaving group hydrophilic and hydrophobic binding sites of cholesterol esterase or both anionic substrate binding site and peripheral anionic binding site of acetylcholinesterase bind to N,N-methyl-alpha-methylbenzyl disubstituted amide parts of these inhibitors and the enzyme does not catalyze the hydrolysis of these inhibitors. The opposite stereopreference (S) for the inhibition of cholesterol esterase by compounds 2 may be due to the fact that N, N-methyl-alpha-methylbenzyl disubstituted amide parts of these inhibitors bind to the alkyl chain binding site of the enzyme. Compounds 3-6 are active site-directed irreversible inhibitors of cholesterol esterase (ki=1-13000 M-1 s-1) and peripheral anionic binding site-directed irreversible inhibitors of acetylcholinesterase (ki=1.7-1300 M-1 s-1). Compounds 3 have low enantioselectivities (E=1.3-1.4) for both enzymes. The stereopreference for atropisomers 4 and 6 is S-form toward both enzymes (E=2-30) and is identical to that of cholesterol esterase-catalyzed hydrolysis of 1,1'-bi-2-naphthyl-2,2'-diacylate. This stereopreference (S) may be due to the fact that the butyryl group or one of two butylcarbamate groups of S-atropisomers binds more effectively to the leaving group hydrophobic binding site of cholesterol esterase or the peripheral anionic binding site of acetylcholinesterase than that of R-atropisomers. The opposite stereopreference (R) for atropisomers 5 toward both enzymes may be due to a favorable interaction between the hydroxyl group of the inhibitors and the leaving group hydrophilic binding site of cholesterol esterase or the peripheral anionic binding site of acetylcholinesterase.     

An assessment of the efficiency of Spanish schools: evaluating the influence of the geographical,managerial, and socioeconomic features

The aim of the present paper is to explore the efficiency of Spanish schools while simultaneously considering data envelopment analysis (DEA) and multivariate analysis. Test scores from the Program for International Assessment reports are used as outputs while the resources of each institution are considered as inputs to the analysis. The methodology utilized determines the DEA efficiencies under various input/output combinations and the results are interpreted through the application of factor analysis and property‐fitting techniques. The objective of the study is to identify the strengths and weaknesses of each type of school and the connections with the way in which the efficiency is obtained. In the light of the results, the study concludes that there exist differences related with two of the criteria considered: the type of management of the schools and the parental socioeconomic level of the students. However, no differences appear when the geographical location of the institutions is considered to characterize the entities.     

Fabrication and evaluation of a passive SU8-based micro direct glucose fuel cell

Microsystem Technologies - A passive micro direct glucose fuel cell (μDGFC) using SU8-current collector structures of 8 × 14&nbsp;mm with a grid that allows the delivery...     

Nano‐Architectured Composite Anode Enabling Long‐Term Cycling Stability for High‐Capacity Lithium‐Ion Batteries

Failure mechanisms associated with silicon‐based anodes are limiting the implementation of high‐capacity lithium‐ion batteries. Understanding the aging mechanism that deteriorates the anode performance and introducing novel‐architectured composites offer new possibilities for improving the functionality of the electrodes. Here, the characterization of nano‐architectured composite anode composed of active amorphous silicon domains (a‐Si, 20 nm) and crystalline iron disilicide (c‐FeSi₂, 5–15 nm) alloyed particles dispersed in a graphite matrix is reported. This unique hierarchical architecture yields long‐term mechanical, structural, and cycling stability. Using advanced electron microscopy techniques, the nanoscale morphology and chemical evolution of the active particles upon lithiation/delithiation are investigated. Due to the volumetric variations of Si during lithiation/delithiation, the morphology of the a‐Si/c‐FeSi₂ alloy evolves from a core‐shell to a tree‐branch type structure, wherein the continuous network of the active a‐Si remains intact yielding capacity retention of 70% after 700 cycles. The root cause of electrode polarization, initial capacity fading, and electrode swelling is discussed and has profound implications for the development of stable lithium‐ion batteries.     

An exploratory study of risk aversion in supply chain dynamics via human experiment and agent-based simulation

The literature on the impact of risk aversion on supply chains (SCs) is relatively limited and, in particular, there is a dearth of theory and a lack of empirical evidence concerning: (1) the impact of individual risk aversion on the generation and dynamics of the order policy (e.g. order patterns and inventory holding costs); (2) the impact of several combinations of risk-averse members in each stage of a multi-echelon SC. We explore these gaps through a multi-method approach (i.e. human experiments and agent-based simulation), thus using both empirical and simulated data. Specifically, based on results from a human experiment, we develop the conjecture that risk aversion is positively correlated to the desired stock level and consequently to the safety stock factor of inventory order policies. Building on this finding, we perform a simulation study to infer the impact of individual risk aversion in a multi-echelon SC. Results show that alternative compositions of the SC in terms of risk aversion levels of the echelons significantly influence inventory holdings and SC dynamics. The study implies that a company facing problems of high inventory days-on-hand should favour low-risk aversion managers, as instrumental to lowering stock and improving net working capital.