Comparison of three Listeria monocytogenes strains in a guinea-pig model simulating food-borne exposure

Three different Listeria monocytogenes strains, LO28 (a laboratory strain with truncated InlA), 4446 (a clinical isolate) and 7291 (a food isolate), were compared in a guinea-pig model designed to mimic food-borne exposure. The objectives were (1) to verify the applicability of the animal model for distinguishing between Listeria with different virulence properties and (2) to explore whether it was possible to reduce the required number of animals by dosing with mixed cultures instead of monocultures. Consistent with in vitro observations of infectivity in Caco-2 cells, faecal densities and presence in selected organs were considerably lower for LO28 than for the other two strains. Additionally, the animal study revealed a difference in prevalence in faeces as well as in internal organs between the clinical isolate and the food isolate, which was not reproduced in vitro . Dosage with monocultures of Listeria strains gave similar results as dosage with a mixture of the three strains; thus, the mixed infection approach was a feasible way to reduce the number of animals needed for determination of listerial virulence.     

VGLUT2-dependent sensory neurons in the TRPV1 population regulate pain and itch

The natural response to itch sensation is to scratch, which relieves the itch through an unknown mechanism. Interaction between pain and itch has been frequently demonstrated, and the selectivity hypothesis of itch, based on data from electrophysiological and behavioral experiments, postulates the existence of primary pain afferents capable of repressing itch. Here, we demonstrate that deletion of vesicular glutamate transporter (VGLUT) 2 in a subpopulation of neurons partly overlapping with the vanilloid receptor (TRPV1) primary afferents resulted in a dramatic increase in itch behavior accompanied by a reduced responsiveness to thermal pain. The increased itch behavior was reduced by administration of antihistaminergic drugs and by genetic deletion of the gastrin-releasing peptide receptor, demonstrating a dependence on VGLUT2 to maintain normal levels of both histaminergic and nonhistaminergic itch. This study establishes that VGLUT2 is a major player in TRPV1 thermal nociception and also serves to regulate a normal itch response.     

Detecting sample misidentifications in genetic association studies

Genetic association studies require that the genotype data from a given person can be correctly linked to the phenotype data from the same person. However, sample misidentification errors sometimes happen, whereby the link becomes invalid for some of the subjects in a study. This can have substantial consequences in terms of power to detect truly associated variants. In family-based studies, Mendelian inconsistencies can be used to detect sample misidentification. Genome-wide association studies (GWAS), however, typically use unrelated individuals, making error detection more problematic. Here we present a method for identifying potential sample misidentifications in GWAS and other genetic association studies building on ideas from forensic sciences. A widely used ad-hoc method for error detection is to check if the sex of an individual matches its X-linked genotype. We generalize this idea to less stringent associations between known genotypes and phenotypes, and show that if several known associations are combined, the power to detect misidentifications increases substantially. Individuals with an unlikely set of phenotypes given their genotypes are flagged as potential errors. We provide analytical and simulation results comparing the odds that the genotype and phenotype are both from the same individual for different numbers of available genotype-p henotype associations and for different information content of the associations. Our method has good sensitivity and specificity with as few as ten moderately informative genotype-phenotype associations. We apply the method to GWAS data from the Danish National Birth Cohort.     

Senescence in oat leaf segments under hypobaric conditions

The physiological effects of storing plants under hypobaric conditions were studied using oat ( Avena sativa L. cv. Victory) leaf segments as a test system. The segments from seven day old plants were floated on water and stored in darkness at 12°C, 1.6 kPa or at 25°C, 6 kPa. Low temperature or hypobaric conditions delayed senescence, whereas the combination arrested the syndrome at an early stage. One of the effects of low pressure was to force the stomata open. The hormones abscisic acid and kinetin, which affect the stomatal aperture and also senescence, did not show any effect in hypobarically stored plant material. The stomata were forced open in darkness when the pressure was lower than 77 kPa and opening time was 8 h. The senescence syndrome in hypobarically stored segments developed similar to those treated with kinetin at 101 kPa.     

Distribution of Bacterial Growth Activity in Flow-Chamber Biofilms

In microbial communities such as those found in biofilms, individual organisms most often display heterogeneous behavior with respect to their metabolic activity, growth status, gene expression pattern, etc. In that context, a novel reporter system for monitoring of cellular growth activity has been designed. It comprises a transposon cassette carrying fusions between the growth rate-regulated Escherichia coli rrnBP1 promoter and different variant gfp genes. It is shown that the P1 promoter is regulated in the same way in E. coli and Pseudomonas putida, making it useful for monitoring of growth activity in organisms outside the group of enteric bacteria. Construction of fusions to genes encoding unstable Gfp proteins opened up the possibility of the monitoring of rates of rRNA synthesis and, in this way, allowing on-line determination of the distribution of growth activity in a complex community. With the use of these reporter tools, it is demonstrated that individual cells of a toluene-degrading P. putida strain growing in a benzyl alcohol-supplemented biofilm have different levels of growth activity which develop as the biofilm gets older. Cells that eventually grow very slowly or not at all may be stimulated to restart growth if provided with a more easily metabolizable carbon source. Thus, the dynamics of biofilm growth activity has been tracked to the level of individual cells, cell clusters, and microcolonies.     

Cytokinin Profiles in the Conifer Tree <Emphasis Type="Italic">Abies nordmanniana</Emphasis>: Whole-Plant Relations in Year-Round Perspective

Conifer trees are routinely manipulated hormonally to increase flowering, branching, or adjust crown shape for production purposes. This survey of internal cytokinin levels provides a background for such treatments in Abies nordmanniana, a tree of great economic interest. Reference points in the crown and root system were sampled destructively in 4- and 6-year-old trees and analyzed for a range of cytokinins by LC-MS/MS. No seasonal patterns were detected in the root samples, and a major portion of cytokinin was in conjugated forms. Dramatic and consistent seasonal changes occurred in the crown, at levels 17–65 times higher than in the root. Predominant among crown cytokinins was ZR, except in the needles where IPR was also prominent. Within the crown, cytokinin profiles in different organs differed consistently. The leader bud showed a pronounced mid-June minimum, and a maximum later in summer. Subapical buds showed the same June minimum but peaked in mid autumn at a much lower level. Maxima in these buds were preceded by peaks in the subapical stem. Parallel patterns were observed in homologous tissues on branches.This pattern is consistent with two surges beginning in the uppermost stem tissues leading to subsequent accumulation or stimulated production within the buds. Strong differential hormonal profiles between adjacent buds with different fates agree with recent evidence of localized cytokinin production. The data suggest a reduced role of root-derived cytokinins in crown development. Practical cytokinin treatments for crown-shape regulation require close attention to dosage as well as precise timing and positioning.