Food recalls caused by pathogens receive considerable public attention due to health risk and the potential loss to the companies involved. There are very few studies analyzing the relationship between food recalls and characteristics of the companies involved. Because of the significance of the problem and lack of available research, the association between food recalls caused by pathogen and characteristics of the companies involved is examined in this thesis. To address the problem, data on food product recalls in the United States from January 2000 to October 2009 are used. Only the events caused by pathogens are analyzed in the thesis. The firms that have multiple recall incidents are the units of analysis. The study employs an econometric model with discrete choice modeling approaches: logit and probit. There are two main hypotheses. Firstly, it is hypothesized that branding decreases the likelihood of the occurrence of the repeated recall event. Secondly, size of the firm is hypothesized to be associated with higher likelihood of recurrence. The major finding is that branding and firm size are associated with higher probability of the recurrence of food recall events associated with pathogenic contamination. A firm that produces branded products is around 15 percent more likely to have a recurrence of food recall events than a firm producing unbranded product. This finding points out the interesting and unexpected issue that branding is not associated with improved performance in food safety. Additionally, an increase in firm size has a minute but significant association with rising likelihood to have a recurrence of a food recall event. This study is the first concerning the firm level factors that can influence risk of the recurrence of food recall incidents involving pathogens. Thus, its results are distinctive and can benefit both government and private sectors with respect to food safety policy or food safety standards.

Thesis (Ph. D.)--Case Western Reserve University, 2009. / [School of Medicine] Department of Physiology and Biophysics. Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 115-138).

Thesis (Ph. D.)--University of Queensland, 2002. / Includes bibliographical references.

The aim of this PhD was to investigate major gaps in our understanding of how mycorrhizal fungi and aphids interact via their effects on plants, and how these interactions regulate emission of plant volatiles and consequently aphid and parasitoid host location. A series of experiments was designed using broad bean (Vicia faba L.), pea aphids (Acyrthosiphon pisum) and their parasitoid wasp, Aphidius ervi and mixed or single spore cultures of AM fungi as a model system. This PhD has determined that arbuscular mycorrhizal fungi are more important drivers of above-ground ecological interactions than ever considered before. They have key roles in specialist aphid host location and in influencing their development. The antagonistic effect of aphids on functioning of mycorrhizal association suggests that the interactions operate in both directions. However, if plants were supplied with phosphorus the aphids did not affect mycorrhizal colonisation suggesting that at sufficient phosphorus availability plants can tolerate the effect of aphids on mycorrhizal colonisation. This demonstrates how dynamic the multi-trophic systems are and that their outcomes are also influenced by soil nutrient availability, with implications for agricultural practices. This PhD has discovered that underground signals carried through common mycelial networks warn neighbouring plants of aphid attack. This signalling allows plants that receive the signal to initiate their defence system by changing their profiles of volatiles emissions and repel aphids and attract their parasitoids so that they may prevent the attack. Because the signal transfer is rapid it incurs the greatest fitness benefit for the receiving plant and potentially also for the donor of the signal and for the fungi. We now need to determine the wider ecosystem implications of this phenomenon, how the signalling is regulated in nature and in agroecosystems and what the fitness consequences are for each component organism.

Incompatible plant/pathogen interactions are often manifested as the hypersensitive response (HR), characterised by host cell death and rapid tissue collapse at the site of attempted infection. A key early response during the HR is the generation of reactive oxygen species (ROS), such as the superoxide anion ( 0; -) and hydrogen peroxide (H20 2), in an oxidative burst. The ROS produced during the oxidative burst have been implicated as cellular signalling molecules for the induction of defences responses including hypersensitive cell death. Increasing evidence exist that the free radical, nitric oxide (NO) also acts as a signalling molecule in plants during plant/pathogen interactions. The generation of NO in response to bacterial challenge, and the potential signalling pathways involved in H20 2- and NO-induced defence responses in Arabidopsis were therefore investigated Arabidopsis suspension cultures were found to generate elevated levels of NO and undergo cell death analogous to HR seen in planta, in response to challenge by avirulent bacteria. Using NO donors, elevated levels of NO were found to be sufficient to induce cell death independently of ROS, but not the expression of the defence-related genes PAL or GST. The NO-induced cell death was sensitive to inhibitors of RNA processing and protein synthesis, suggesting that NO-induced cell death is a form of programmed cell death (PCD), requiring the expression of at least one gene. However, the source of NO production by Arabidopsis remains to be elucidated, but appears to be independent of nitric oxide synthase-like activity. Pharmacological studies using specific inhibitors of mammalian mitogen activated protein kinase (MAPK) signalling cascades, and guanylate cyclase, the enzyme responsible for the production of second messenger cyclic guanosine monophosphate (cGMP), suggest that a MAPK signalling cascade acts downstream or independently of the oxidative burst to initiate H20 2-induced defence responses, while NO-induced cell death requires the production of cGMP in Arabidopsis. A number of studies have attempted to establish whether PCD induced during the HR in plants is similar to apoptotic cell death of anin1al cells. The key executioners of apoptosis in animal cells are caspases. NO was found to induce caspase-like activity in Arabidopsis cells, while a specific inhibitor of caspase-l blocked harpin-, H20 2- and NO-induced cell death. A characteristic of apoptosis is chromatin condensation and DNA fragmentation into nucleosomal fragments. Chromatin condensation was observed in Arabidopsis cells treated with the NO donor Roussin's black salt, but no DNA fragmentation was found in DNA extracted from cells treated with harpin, H20 2 or NO. In addition, random DNA degradation indicative of necrosis was found in DNA extracted from cells following avirulent bacterial challenge.

Pathogens are one of the prevalent stresses to plants. Resistance mediated by the resistance genes is efficient mechanism for evading the pathogens. To understand the influence of various biotic and abiotic factors on resistance gene promoters, plants having N gene promoter fused with reporter genes were developed. Experiments with tobacco plants revealed that on tobacco mosaic virus infection, the N protein may increase in the cells. Also, extreme temperature may result in decrease in the N protein. The salicylic acid produced during the development of systemic acquired resistance does not hinder the N promoter function. Hence, it can be concluded that the promoter region of resistance genes can be influenced by many biotic and abiotic factors. In the tobacco plants lacking the N gene, infection with tobacco mosaic virus leads to generation of systemic recombination signal. Experiments suggest that this signal can lead to better tolerance of the pathogen in next generation. Also, in the plants which received systemic recombination signal, the resistance gene loci are hypermethylated and the frequency of rearrangement in these loci increases. Hence, the signal results in higher tolerance to pathogen and increased genetic variability in resistance genes. / xvi, 147 leaves : ill. (some col.) ; 29 cm.

No description available.

Multiple parameters were monitored during an 18-month period in two karst groundwater basins in Woodford County, Kentucky, in order to assess the effects of land use on water quality. Blue Hole Spring drains a primarily urban area, whereas spring SP-2 drains an agricultural area. Water-quality parameters were monitored manually weekly or biweekly, as well as more frequently during storms. Discharge (Q), temperature (T), specific conductance (SC), and turbidity were continuously monitored and logged at 15-minute intervals. It is hypothesized that pathogen and sediment concentrations would be lower at SP-2 than at Blue Hole Spring due to differences in land use between basins. Average Q was greater at Blue Hole than at SP-2, and SC values were greater at Blue Hole than at SP-2 for 70 of 71 sample sets. During two monitored storms, as Q increased, SC decreased and turbidity increased. Biweekly Blue Hole fecal coliform (FC), total coliform (TC), and atypical colonies (AC) values averaged 160, 3,600, and 40,000 cfu/100 mL, respectively, and fluctuated more than at SP-2. Biweekly SP-2 FC, TC, and AC values averaged 130, 2,000, and 8,300 cfu/100 mL, respectively. Biweekly values for AC/TC averaged 14.29 at Blue Hole and 6.27 at SP-2. AC/TC ratios were greater at Blue Hole than at SP-2 for 29 of 31 biweekly sample sets. There is a statistically significant difference between the biweekly data sets from the two sites, as well as between data collected under WET and NORMAL flow conditions at each site. Male-specific coliphage (MSP) was detected in most samples collected from Blue Hole, but was never detected at SP-2. Given the proximity of the basins, differences in water quality appear to reflect differences in land use, as hypothesized. Results were similar to other studies in the Inner Bluegrass region. For both Blue Hole and SP-2, wet weather was associated with changes in certain parameters. This study has also shown that the AC/TC ratio appears to be a valid tool for determining the source of contamination within karst ground-water systems as well as in surface water.

No description available.