Browsing by Subject "Salmonella"

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    Entwicklung und Validierung schneller und selektiver Verfahren zum Nachweis von Salmonella enterica, Cronobacter spp. und Bacillus cereus in Milcherzeugnissen
    (2014) Zimmermann, Jennifer; Schmidt, Herbert
    The presence of pathogens is a serious problem in the food industry and contaminations of food with Bacillus cereus, Cronobacter spp. and Salmonella enterica are responsible for a large number of diseases worldwide. Milk products like milk, whey or cream powder are widely used in industry as an ingredient in other foods. Therefore it requires a fast and reliable identification of pathogenic microorganisms. The official methods according to § 64 LFGB or ISO/TS 22964 apply a common scheme of pre-enrichment, selective enrichment, detection and confirmation and take between three and six days. The aim of this work was the development and validation of a real-time PCR based method, which identifies the existence of the three pathogens in dairy products within 24 hours. The identification of B. cereus, Cronobacter spp. and S. enterica with the developed TaqMan real-time PCR was performed using specific genetic characteristics and an internal amplification control to eliminate false negative results. For B. cereus, the groEL gene, which codes for a heat shock protein, was selected as target. For the detection of Cronobacter spp. the ompA gene and for S. enterica the invA gene was chosen. Both genes are responsible for the invasion of the pathogens in the human epithelial cells. The adaptation of the method to the food matrix and an optimization of the enrichment time were affected by an artificial contamination of various dry dairy products. It was possible to detect 105 cfu/g C. sakazakii and S. Enteritidis cells with an initial concentration of 100 cfu/g in reconstituted powdered infant formula after enrichment of six hours. To simulate a natural contamination, powdered infant formula was contaminated with desiccated C. sakazakii cells in various concentrations and analyzed with the developed real-time PCR method. It was possible to detect an inoculum concentration of 0.01 CFU/g dry stressed C. sakazakii cells at low aw values (0.22). The new TaqMan real-time PCR is fast, reliable and specific for the clearly detection of the three major pathogenic microorganisms in milk products and was carried out within 24 hours.
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    Improving food safety of sprouts and cold-smoked salmon by physical and biological preservation methods
    (2007) Weiss, Alexander; Hammes, Walter
    The safety of raw, ready-to-eat foods is of paramount importance and is in the focus of the food industry, consumers as well as food scientists. To improve the food safety status of the products, efficient decontamination as an important processing step and/or the use of protective microorganisms as biocontrol agents are promising approaches. In our work we successfully used these approaches for raw sprouts and cold-smoked salmon as examples for RTE foods. Therefore the set goals have been successfully performed and essential scientific knowledge has been contributed. The results have been published and are described in the following in form of the respective abstracts. Thermal seed treatment to improve the food safety status of sprouts: Alexander Weiss and Walter P. Hammes. 2003. Thermal seed treatment to improve the food safety status of sprouts. (Journal of Applied Botany. 77: 152-155) Efficacy of heat treatment in the reduction of salmonellae and Escherichia coli O157:H? on alfalfa, mung bean and radish seeds used for sprout production: Weiss Alexander and Hammes, Walter P. 2005. Efficacy of heat treatment in the reduction of salmonellae and Escherichia coli O157:H? on alfalfa, mung bean and radish seeds used for sprout production. (Eur. Food Res. Tech. 211, 187-191) Characterization of the microbiota of sprouts and their potential for application as protective cultures: Alexander Weiss, Christian Hertel, Silke Grothe, Diep Ha and Walter P. Hammes 2006. Characterization of the microbiota of sprouts and their potential for application as protective cultures. (Applied and Environmental Microbiology. Submitted for publication) Lactic acid bacteria as protective cultures against Listeria spp.on cold-smoked salmon: Weiss Alexander and Hammes, Walter P. 2006. Lactic acid bacteria as protective cultures against Listeria spp.on cold-smoked salmon. (Eur. Food Res. Tech. 222, 343-346)
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    Stress hormone-induced immunomodulation and interplay between immune cells and bacteria in response to stress hormones in domestic pigs
    (2020) Reiske, Lena; Stefanski, Volker
    The two main endocrine systems involved in the regulation of stress reactions are the HPA axis, leading to the synthesis of glucocorticoids like cortisol or corticosterone, and the SAM axis, whose activation is associated with the release of the catecholamines adrenaline and noradrenaline. These stress hormones modulate the function of the immune system. Although pigs in modern husbandry systems face many stressors, the consequences of elevated plasma stress hormone levels on porcine immune cell numbers and functionality are insufficiently resolved. While some research on glucocorticoid effects has been conducted, data on many parameters are missing and catecholamines have not been studied systematically in the pig, yet. It is known that stress can negatively affect pigs’ resistance to infections like salmonellosis, but the underlying mechanisms are still subject to intense research efforts, with new perspectives arising since the discovery of interkingdom-signalling and microbial catecholamine perception. The aim of this thesis was to determine the effects of cortisol, adrenaline and noradrenaline on porcine immune cell functionality and the blood numbers of different leukocyte subsets. Furthermore, the interplay of immune cells and Salmonella Typhimurium under the influence of catecholamines was investigated. Adult male castrated pigs were surgically equipped with indwelling catheters to enable stress-free blood collection and intravenous application of hormones. In an initial experiment, the effects of in vitro stress hormone treatment on lymphocyte proliferation and the production of the proinflammatory cytokine TNFa were described. Cortisol reduced both proliferation and number of TNFa producers. Both catecholamines caused an increased lymphocyte proliferation at low concentrations whereas noradrenaline drastically decreased proliferation at high concentrations. While noradrenaline had no impact on TNFa producers, they were reduced in gd T cells and monocytes upon adrenaline addition. Overall, the effects were comparable to humans in terms of direction and dose but there were some disparities regarding adrenaline. In the second part of the project, the impact of in vivo stress hormone administration on immune cell numbers and functionality was examined by infusion for 48h. Cortisol and noradrenaline led to a decreased lymphocyte proliferation but to a variable extent and all three hormones promoted phagocytic function of innate immune cells. Cortisol caused a marked increase of neutrophil numbers while almost all other cell types declined strongly. For most cell types, noradrenaline exerted similar effects but solely after 2h whereas cortisol-induced alterations lasted the whole treatment period. Adrenaline effects were mostly reduced to CD8- T cells, which were reduced at first but increased after 24h. A sharp peak in NK cell numbers after 2h adrenaline infusion is particularly noteworthy and resembles findings from rodent and human studies. Overall, both hormone groups led to a shift from adaptive to innate immunity, underpinning the picture of a promotion of fast and unspecific defence systems to respond to threats in stressful situations. In a third study, S. Typhimurium was grown in the presence of catecholamines to determine the effects of supernatants from these cultures on porcine immune cell function. Both lymphocyte proliferation and TNFα production were hampered substantially, as opposed to the findings on catecholamine effects in the first experiment. It was demonstrated that these effects were not caused by catecholamines or their oxidation products and the formation of a so-far unknown immunosuppressive substance by catecholamine-primed bacteria was assumed. The results contribute to a better understanding of the increased susceptibility to infection in stressed animals and reveal a new dimension of cross-species communication. Finally, the results of the present thesis were discussed regarding their comparability to studies in humans and rodents and previous stress experiments in pigs. Furthermore, the effects of acute and chronic stress as well as different coping styles that are characterised by a SAM or HPA predominance on animal welfare and pig health were discussed, based on the endocrine mechanisms investigated in the present thesis. Possible implications of enhanced glucocorticoid and catecholamine levels for practical pig husbandry were given. Lastly, suggestions for future research to further elucidate the impact of stress hormones on the porcine immune system and the interplay with pathogenic bacteria were made.