177,389 research outputs found
Listeria monocytogenes : detection and behaviour in food and in the environment
No full textIn this thesis, Listeria monocytogenes, a bacterial pathogen was studied, with emphasis on the detection and behaviour in food and environment.Epidemics of foodborne listeriosis have raised concern about the incidence of L. monocytogenes in foods. In the past 10-15 years listeriosis has emerged as a foodborne illness in a series of large outbreaks from contaminated milk, coleslaw, soft cheese and paté. The organism is ubiquitous in the environment and has been isolated from a variety of raw and ready-to-eat food products.As there is a lack of reliable enrichment procedures, factors influencing the isolation, confirmation and identification of L. monocytogenes were investigated. It was shown that the other (faster growing) listerias can mask the presence of this pathogen in enrichment media. The use of lithium chloride did not overcome this effect. It was also observed that the use of acriflavine in enrichment media affected the isolation of L. monocytogenes both directly and indirectly. Because these effects will lead to inferior detection of L. monocytogenes, it is worthwhile to introduce an isolation medium on which the pathogen can be differentiated from non-pathogenic listerias. On enhanced hemolysis agar (EHA), L. monocytogenes can be distinguished from other listerias on the basis of hemolysis.The traditional methods for the detection of L. monocytogenes are both time consuming and labour intensive. Therefore, rapid test kits for Listeria and L. monocytogenes have been developed. Differences among the various test kits may be contributed to the enrichment protocols, the detection limits of the tests and the concentration of Listeria cells in the samples.In the second part of this thesis, the behaviour of L. monocytogenes in food and environment was investigated.In the literature contradictory results on the growth of the organism on meat surfaces have been reported. In this study it was shown that growth on raw meat was strain dependent and mainly determined by initial pH and storage temperature. On cooked meat products the growth was not or only slightly affected by the storage atmosphere and the presence of lactic acid bacteria. At the end of shelf life, levels of 10 7cfu per g could be reached.Under osmotic stress conditions exogenously added proline, betaine and carntine significantly stimulate growth in laboratory media. Because these compounds are also present in foods, they can contribute to growth of L. monocytogenes in various foods at high osmolarities.In sporadic cases of listeriosis it is often difficult to link food products with this disease, unknown sources may also be responsible for illness. From an investigation in the domestic environment it became clear that L. monocytogenes may be present in high numbers.To be able to control the problems caused by L. monocytogenes, international microbiological criteria, based on 2L. monocytogenes cells per gram on sell-by-date should be established. Persons at risk (immuno-compromized, pregnant) should be strongly advised not to eat food products likely to contain the pathogen. Meanwhile, more attention should be given to challenge studies, factory ecology, cleaning and disinfection and both personal and domestic hygiene
Phenotypic and genotypic characterization of sorbitol-negative of slow-fermenting (suspected O157) Escherichia coli isolated from milk samples in Lombardy region
No full textAims: To investigate phenotypic and genotypic aspects of sorbitol-negative or slow-fermenting Escherichia coli, suspected to belong to O157 serogroup, isolated in Italy. Methods and Results: Milk samples originating from goats and cows were screened for the presence of E. coli O157 with cultural methods. Sorbitol-negative or slow-fermenting strains were subjected to phenotypic characterization, antibiotic resistance profiles, PCR reactions for detection of toxins (stx(1) and stx(2)) and intimin (eae(GEN) and eae(O157)) genes and clustering by pulsed field gel electrophoresis (PFGE). Only one strain revealed to be O157. Susceptibility to 11 antibiotics highlighted the high resistance to tetracycline (50%), sulfonamide and streptomycin (33%). The stx(2) gene was detected in two strains; only the strain identified as O157 exhibited an amplicon for both eae genes. PFGE identified seven distinct XbaI macrorestriction patterns at a similarity level of 41%. Conclusions: The use of sorbitol fermentation as cultural method is not sufficient for STEC discrimination while PCR assay proved to be a valuable method. Significance and Impact of the Study: The study reports presence of Shiga toxin-producing E. coli in raw milk, signalling a potential risk for humans
Pharmacology and pharmacokinetics of tazemetostat
No full textTazemetostat, a novel oral selective inhibitor of enhancer of zeste homolog 2 (EZH2), was approved by the Food and Drug Administration (FDA) in 2020 for use in patients with advanced epithelioid sarcoma or relapsed/refractory (R/R) EZH2-mutated follicular lymphoma. These indications were approved by the FDA trough accelerated approval based on objective response rate and duration of response that resulted from phase 2 clinical trials. Tazemetostat competes with S-adenosylmethionine (SAM) cofactor to inhibit EZH2, reducing the levels of trimethylated lysine 27 of histone 3 (H3K27me3), considered as pharmacodynamic marker. Tazemetostat is orally bioavailable, characterized by rapid absorption and dose-proportional exposure, which is not influenced by coadministration with food or gastric acid reducing agents. It highly distributes in tissues, but with limited access to central nervous system. Tazemetostat is metabolized by CYP3A in the liver to 3 major inactive metabolites (M1, M3, and M5), has a short half-life and is mainly excreted in feces. Drug-drug interactions were shown with moderate CYP3A inhibitors as fluconazole, leading the FDA to recommend a 50% dose reduction, while studies investigating coadministration of tazemetostat with strong inhibitors/inducers are ongoing. No dosage modifications are recommended based on renal or hepatic dysfunctions. Overall, tazemetostat is the first-in-class EZH2 inhibitor approved by the FDA for cancer treatment. Current clinical studies are evaluating combination therapies in patients with several malignancies
Analogues of Neuropeptide Y Containing β-Aminocyclopropane-carboxylic Acids are the Shortest Linear Peptides Selective for the Y₁-Receptor
No full textKoglin N, Zorn C, Beumer R, et al. Analogues of neuropeptide Y containing beta-aminocyclopropane carboxylic acids are the shortest linear peptides that are selective for the Y-1 receptor. Angewandte Chemie International Edition. 2003;42(2):202-205
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
Synthesis of novel simplified sarcodictyin/eleutherobin analogs with potent microtubule-stabilizing activity, using ring closing metathesis as the key-step
No full textThe synthesis of a number of novel simplified eleutheside analogs with potent tubulin-assembling and microtubule-stabilizing properties is described. using ring closing metathesis as the key-step for obtaining the 6-10 fused bicyclic ring system. The RCM precursors were synthesized starting from aldehyde 3 [prepared in 6 steps on a multigram scale from R-(-)-carvone in 30% overall yield] via multiple stereoselective Brown allylations. Second generation RCM catalyst 13 gave the desired ring closed 10-membered carbocycles as single Z stereoisomers in good yields. The RCM stereochemical course (100% Z) likely reflects thermodynamic control. The crucial role of the protecting groups of the homoallylic and allylic substituents for the efficiency of the RCM reactions is discussed. These simplified analogs of the natural product (lacking inter alia the C-4/C-7 ether bridge) retain potent microtubule-stabilizing activity. However, the cytotoxicity tests did not parallel the potent tubulin-assembling and microtubule-stabilizing properties: limited cytotoxicity was observed against three common tumor cell lines (human ovarian carcinoma and human colon carcinoma cell lines, IC50 in the muM range given in Table 2), three orders of magnitude less than paclitaxel (IC50 in the nM range). (C) 2003 Elsevier Ltd. All rights reserved
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Immunoglobulin adsorption on modified surfaces
No full textPreservation of biological functioning of proteins during immobilisation is of special interest in various biomedical and biotechnical applications. In industry physical adsorption of immunoglobulins (IgGs) onto solid surfaces is still the predominant immobilisation procedure because it is relatively easy to perform. Physical adsorption, however, often results in an undesired loss of biological activity. This loss of activity may be caused by changes in the specific folding (the conformation) of the IgG or by a reduced accessibility of the antigen binding sites by blocking, for instance when IgG molecules are adsorbed with their antigen binding sites oriented towards the sorbent surface.To control the orientation and conformation of adsorbed IgG molecules we studied the interactions involved in physical adsorption of IgG molecules on solid surfaces. Our goal was to optimize the biological activity of adsorbing IgG molecules. For this, we introduced a new method to achieve oriented physical adsorption of IgG. This concept is based on the anisodimensionality of IgG molecules and resembles 'molecular sieving' on the sorbent surface. The 'sieve' is created by preadsorbed molecules that form a steric barrier preventing adsorption at some sites, but leaving patches of uncovered surface area. The open areas in the preadsorbed layer can be tuned in such a way that only the smaller part of anisodimensional molecules can enter and adsorb. In the case of 19G this means that only the Fc part can adsorb to the surface and thereby forcing the larger antigen binding parts (F(ab) 2 ), directed towards the solution and, hence, accessible to bind antigens. A 'sieve' formed either with preadsorbed IgG molecules or with triblock copolymers of poly(ethylene oxide), PEO, and poly(propylene oxide), PPO, of the type PEOPPO-PEO was proven to yield a higher specific biological activity of subsequently adsorbing IgG.In brief, the effect of a 'molecular sieve' on IgG adsorption is essentially threefold. Firstly, it induces oriented IgG adsorption. Secondly, it prevents extended undesirable structural changes in adsorbed IgG and thirdly, it prevents undesirable reorientation of the adsorbed IgG.In chapter 1 it is explained that in many applications there is a need to control the biological activity of adsorbed IgG. The physical properties and characteristics ofIgG molecules and the interactions involved in physical adsorption of proteins are described and, more importantly, our variant of 'molecular sieving' is introduced. Finally, an outline of this thesis is given.The influence of electrostatic interactions on the adsorption of IgG is examined both theoretically and experimentally in chapter 2. The long range interaction between IgG and the sorbent surface is treated in terms of the DLVO theory. We attempted to make use of the dipolar character of the IgG molecules to control their orientation upon adsorption. It is concluded that electrostatic interactions have a strong influence on the adsorption behaviour of IgG molecules on hydrophilic charged surfaces. Due to extensive desorption of IgG from both positively and negatively charged surfaces, electric field-induced orientation of IgG could not be established unambiguously.Chapter 3 is mainly dedicated to the orientational aspects of IgG adsorption. In this chapter the phenomenon of 'molecular sieving' is demonstrated first theoretically using a Random Sequential Adsorption (RSA) model and second experimentally by a set of reflectometry experiments on surfaces partially covered with preadsorbed layers of either IgG or triblock copolymers of PEO-PPO-PEO. The rate of IgG adsorption and the maximum adsorbed amount decreases with increasing adsorbed amount of triblock copolymer. On the precoated layers, IgG is indeed adsorbed in a preferential orientation which yielded a higher specific biological activity of the IgG molecules. Furthermore, we observed that the preadsorbed layers prevent undesirable reorientation of adsorbed IgG.The mass flux towards the surface also has a profound effect on the adsorbed amount and, consequently, on the orientation of IgG.In chapters 4, 5 and 6 conformational changes in IgG are studied. In chapter 4 a structural analysis of a monoclonal lgG adsorbed on different silica surfaces (hydrophilic, hydrophobic, hydrophobic with preadsorbed triblock copolymers) using ATR-FTIR spectroscopy is given. The secondary structure of adsorbed IgG on a hydrophilic silica surface resembles that of native 19G in solution. The presence of preadsorbed triblock copolymers on the hydrophobic silica surface cause a decrease in the adsorbed amount of IgG and, more importantly prevent substantial structural rearrangements in the adsorbed IgG molecules.In chapters 5 and 6, Circular Dichroism (CD) is used as a spectroscopic technique for studying protein structure in the adsorbed state. Chapter 5 gives information on the structural changes of IgG molecules induced by adsorption on a hydrophobicsurface and compares these changes with those induced by heat treatment. Neither heatinduced nor adsorption-induced structural changes lead to complete unfolding into an extended polypeptide chain, but leave a significant part of the IgG molecule in a globular or corpuscular form. The structural changes induced by heating and by adsorption are different.The effect of preadsorbed IgG and triblock copolymer molecules on the secondary structure of subsequently adsorbing IgG molecules is studied in chapter 6. Structural rearrangements were less extensive with increasing surface coverage of the polymer. It was found that preadsorbed IgG molecules have comparable effects on the secondary structure of subsequent adsorbing IgG; a more native-like structure is retained for the higher adsorbed amounts. Hence, partial pre-coating of a surface is an effective way to control the secondary structure of later adsorbed IgG molecules.To examine whether the model results apply to industrially manufactured diagnostic methods we implemented in chapter 7 the triblock copolymer preadsorption procedure in a microplate assay. Radio-actively labelled IgG and hCG molecules allowed us to monitor the adsorption of IgG and the subsequent specific binding of hCG. The data obtained are in agreement with our earlier model studies and demonstrate that sieving of the IgG by the polymer does take place, resulting in the creation of a more favourably oriented IgG layer. Our studies indicate that the amount of precoated material is critical in the formation of an operational 'sieve'.</p
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