Les Escherichia coli enterohémorragiques (EHEC) sont responsables de maladies graves comme la colitehémorragique (CH), le syndrome hémolytique et urémique (SHU) ou le purpura thrombotiquethrombocytopénique (PTT). Les infections humaines sont principalement dues à la consommationd’aliments contaminés, en particulier la viande d’origine bovine, le lait ou les légumes. Le principalréservoir naturel des EHEC est le tractus gastro-intestinal (TGI) des bovins. Les fèces de bovins sont, parconséquent, responsables de la contamination de plusieurs types d’aliments mais également de ladissémination environnementale de ces bactéries pathogènes. En relation avec cette problématique, lesdeux objectifs de ce projet étaient (i) de développer une nouvelle méthode d’immuno-capture pouraméliorer l’isolement des principaux sérogroupes de EHEC impliqués dans les infections humaines; et (ii)de développer un nouveau DFM (direct fed microbial) utilisable chez les bovins pour diminuer laprévalence des EHEC chez les animaux. Cette thèse a permis le développement d’une méthoded’immuno-capture basée sur l’utilisation d’une microplaque à 96 puits, coatée avec des anticorpsspécifiquement dirigés contre E. coli O157 ou d’autres sérogroupes. Cette méthode, appelée immunomicroplatecapture (IMC) est efficace et facile d’utilisation pour l’isolement de souches d’E. coli O157 ;O26 ; O103 et O111 dans les produits alimentaires. L’IMC pourrait être une alternative à l’utilisation desbilles immuno-magnétiques qui sont classiquement utilisées pour la détection des EHEC dans lesproduits alimentaires, mais qui représentent une technique longue et fastidieuse lors de l’analysesimultanée de nombreux échantillons. La seconde partie de cette thèse a permis de sélectionner 5souches de bactéries lactiques qui présentent une activité antagoniste vis-à-vis d’E.coli O157 et d’autressérogroupes in vitro. La résistance de ces souches aux conditions du tractus gastro-intestinal (conditionsacides, présence de sels biliaires, présence de jus de rumen) a été évaluée in vitro. Leur innocuité a étévérifiée chez des souris Balb-C par l’administration de chacune des souches incorporées à la nourriture(109 cfu/g). Enfin, la lyophilisation des souches n’a pas affecté leur activité antagoniste in vitro. Lesrésultats obtenus dans les différents tests in vitro suggèrent que les 5 souches pourraientpotentiellement être utilisées comme DFM chez les bovins pour diminuer la colonisation de leur TGI parles EHEC et par conséquent diminuer le risque de contamination des aliments et le risque dedissémination environnementale. / Enterohemorrhagic E. coli (EHEC) are responsible for important diseases such as hemorrhagic colitis,hemolytic and uremic syndrome or thrombotic thrombocytopenic purpura. Human infections occurprincipally by consumption of contaminated food particularly beef meat, milk or vegetables. The mainnaturally reservoir of EHEC is the gastro-intestinal tract of cattle. Cattle feces are therefore responsiblefor contamination of various types of food but also environment dissemination of the pathogenicbacteria. Related to this problematic, the two objectives of this project were (i) to develop a newimmuno-capture method to improve the isolation of the main serogroups of EHEC involved in humaninfections in food; and (ii) to develop a new direct fed microbial usable in cattle to decrease prevalenceof EHEC in animals. This thesis allowed the development of an immuno-capture method based on theuse of 96-well microplates coated with specific antibody directed against E. coli O157 and otherserogroups. This method, called immuno-microplate capture (IMC) was efficient and user-friendly forthe isolation of E. coli O157; O26; O103 and O111 in foods. This could be an alternative to the use ofimmuno-magnetic beads which are currently used for the detection of EHEC in foods, but are timeconsumingand labor intensive when large number of samples is analyzed simultaneously. The secondpart of this thesis allowed the selection of 5 lactic acid bacteria strains which presented highantagonistic activity against E. coli O157 and other serogroups in vitro. Resistance of these strains togastro-intestinal conditions (acidic conditions, presence of bile salts and rumen fluid) was evaluated invitro. The safety of the 5 strains was checked in Balb-C mice by administration of each strain mixed infeed at 109 cfu/g. Finally, freeze-drying did not affect the antagonistic activity of the 5 strains, suggesteda possible large scale use of these strains. According to the various results obtained in vitro, the 5 strainscould potentially be used as DFM in cattle to decrease colonization of their gastro-intestinal tract byEHEC and consequently decrease the risk of food and environment contaminations.

Master of Science / Food Science Institute / Randall K. Phebus / The USDA declared seven STEC serotypes to be adulterants in raw, non-intact beef products due to their severe health implications. STEC contamination of carcasses is most likely to occur during hide removal. This study evaluated the efficiency of a mixed STEC-7 inoculum to attach to raw beef carcasses (predominantly lean muscle and adipose tissue), and compared the efficacy of 4.5% lactic acid (LA) to a water (W) spray to reduce STEC populations. Four carcass contamination scenarios, representing potential points whereby STEC could come into contact with raw beef surfaces during slaughter operations, were evaluated: (A) pre-rigor surface STEC inoculated (ca. 7 log cfu/cm[superscript]2), 30-min ambient temperature attachment, spray with LA or W; (B) pre-rigor inoculated, 24-h chilled attachment, spray; (C) tissue chilled 24 h, inoculated, 30-min attachment, spray; and (D) tissue chilled 24 h, rewarmed to 30°C, inoculated, 30-min attachment, spray. Predominantly lean muscle and adipose tissue were collected from four fed cattle immediately after harvest and assigned to the four scenarios for STEC inoculation, followed by a post-inoculation water (control) or LA spray. Tissue excision samples were collected pre- and post-treatment and analyzed to enumerate STEC-7 populations. Data were collected in a completely randomized design and analyzed using a mixed-model ANOVA. Pairwise comparisons of treatment means were made at α = 0.05 with p-values adjusted using Tukey-Kramer. Initial STEC attachment levels to predominantly lean muscle and adipose tissues were not significantly different across all scenarios. Scenarios C and D showed greater STEC attachment compared to scenarios B and A. The LA spray reduced STEC levels more effectively than water across all scenarios. A significant treatment by tissue type interaction was observed for STEC reductions. A greater STEC reduction was observed for adipose tissue than for predominantly lean muscle when lactic acid spray was applied. A significant treatment by scenario interaction was observed for STEC reductions. Scenarios A and B presented greater log reductions (1.77 ± 0.27 and 1.85 ± 0.25 log CFU/cm[superscript]2, respectively) than scenario C (1.04 ± 0.10 Log CFU/cm[superscript]2). LA spray presented the same level of effectiveness when applied to pre-rigor warm tissues and chilled tissues for reducing STEC. Greater post-LA spray reductions were observed when STECs were inoculated onto pre-rigor meat surfaces and submitted to a 24 h chill cycle, suggesting that cold storage temperatures (~2 °C) may stress or injure the STEC cells prior to subsequent antimicrobial spray applications to chilled surfaces. For laboratory studies, consideration must be given to when inocula are applied to tissue surfaces to accurately determine and/or compare the effectiveness of antimicrobial treatments. These findings provide insight to beef processors and researchers regarding inoculation protocols for comparative validation studies, and potential impacts on microbiological results from application of antimicrobial interventions at different points during raw beef processing.

No description available.

As Enfermidades Transmitidas por Alimentos representam um crescente e relevante problema de saúde pública. Além do prejuízo social, a contaminação de alimentos com microrganismos patogênicos gera um enorme prejuízo econômico. Técnicas de Análise de Risco permitem mensurar de forma mais adequada o impacto dos microrganismos contaminantes de alimentos na saúde da população. Uma Análise de Riscos, associada a uma combinação patógeno-alimento, envolve três passos: avaliação do risco, gestão do risco e comunicação do risco. Uma das etapas da avaliação do risco é a avaliação da exposição, baseada em dados sobre freqüência e nível de contaminação dos alimentos pelo patógeno avaliado no alimento em questão, o nível atingido pelo patógeno no momento do consumo e os padrões de consumo. Os produtos cárneos são os principais alimentos responsáveis pela veiculação de patógenos ao homem e os microrganismos de maior relevância nestes produtos são Listeria monocytogenes, Salmonella spp., Campylobacter spp. e Escherichia coli produtora de toxina de Shiga. O objetivo do presente estudo foi levantar informações qualitativas e quantitativas desses quatro patógenos em produtos cárneos (salsicha bovina, lingüiça suína, carne bovina moída e coxa de frango) comercializados no município de São Paulo, de forma a contribuir com dados para futuras avaliações de risco em relação a estes microrganismos nestes produtos. Das 552 amostras de produtos cárneos analisadas, L. monocytogenes foi o patógeno isolado com maior freqüência, sendo detectado em 48,7% das amostras, seguido por Campylobacter spp. em 6,0% e Salmonella spp. em 5,8%. E. coli produtora de toxina de Shiga não foi detectada em nenhuma das amostras estudadas. Listeria monocytogenes foi detectada em todos os tipos de produtos cárneos estudados, com freqüências mais elevadas nas amostras de carne bovina moída (59,4%), seguido de coxa de frango (58,0%), lingüiça suína (39,8%) e salsicha bovina (37,7%). Na maioria das amostras (94,4%), as contagens de L. monocytogenes foram inferiores a 102 UFC/g. As cepas de L. monocytogenes apresentaram ampla distribuição, sendo detectados os quatro grupos de sorotipos: 28,7% pertenceram ao Grupo 1 (sorotipos 1/2a e 3a), 21,0% ao Grupo 2 (sorotipos 1/2c e 3c), 17,0% ao Grupo 3 (sorotipos 1/2b, 3b e 7) e 13,8% ao Grupo 4 (sorotipos 4b, 4d e 4e). Salmonella spp. foi detectada em 32 amostras, sendo 20 (14,5%) de lingüiça e 12 (10,6%) de coxa de frango. As contagens foram baixas, variando de 3,0 a 9,3x10 NMP/g e os sorovares mais freqüentemente isolados foram S. Typhimurium (28,1%), S. Enteritidis (12,5%), S. Derby (12,5%) e S. I 4,[5],12:i:- (12,5%). Campylobacter spp. foi detectado em 33 amostras (6,0%), sendo 27 de coxa de frango (19,6%) e seis amostras de carne moída (4,3%). A presença de L. monocytogenes, Salmonella spp. e Campylobacter spp. nos produtos cárneos analisados representa um risco à saúde da população. O consumo destes produtos quando submetidos à cocção inadequada e/ou a contaminação cruzada com outros alimentos pode levar a ocorrência de Enfermidades Transmitidas por Alimentos. / Foodborne Diseases represent an increasingly important public health problem. Besides the social losses, contamination of food with pathogenic microorganisms generates an enormous economic damage. A more accurate measurement of the impact of microorganisms in food health can be achieved using Risk Analysis techniques. A risk analysis is composed by three elements: risk assessment, risk management and risk communication. One of the four steps of a risk assessment is the exposure assessment, based on data on frequency and level of contamination of a food by the pathogen under evaluation, levels of the pathogen in the food at the time of consumption and consumption patterns. Meat products are the main vehicles of pathogens to humans, where Listeria monocytogenes, Salmonella spp., Campylobacter spp. and Shiga toxin-producing Escherichia coli are the most relevant pathogens. The aim of this study was to obtain qualitative and quantitative information on these four pathogens in four types of meat products (beef sausage, pork sausage, ground beef and chicken leg) marketed in the city of Sao Paulo in order to contribute with data for future risk assessments for these microorganisms in these products. L. monocytogenes is the most frequent pathogen in the 552 samples of meat products analyzed, being detected in 48.7% of the samples, followed by Campylobacter spp. 6.0% and Salmonella spp. 5.8%. Shiga toxin-producing E. coli was not detected in any sample. L. monocytogenes was detected in all types of meat products, with highest frequency in ground beef (59.4%), followed by chicken leg (58.0%), pork sausage (39.8%) and beef sausage (37.7%). In most samples (94.4%), the counts of L. monocytogenes were below 102 CFU/g. L. monocytogenes strains were widely distributed in the four groups of serotypes: 28.7% belonged to Group 1 (serotypes 1/2a and 3a), 21% to Group 2 (serotypes 1/2c and 3c), 17% to Group 3 (serotypes 1/2b, 3b and 7) and 13.8% to Group 4 (serotypes 4b, 4d and 4e). Salmonella spp. was detected in 32 samples, being 20 (14.5%) of pork sausage and 12 (10.6%) of chicken leg. The counts were low, ranging from 3.0 to 9.3 x 10 MPN/g and the most frequent serovars were S. Typhimurium (28.1%), S. Enteritidis (12.5%), S. Derby (12.5%) and S. I 4, [5], 12: i: - (12.5%). Campylobacter spp. was detected in 33 samples (6.0%), being 27 of chicken leg (19.6%) and six samples of ground beef (4.3%). The presence of L. monocytogenes, Salmonella spp. and Campylobacter spp. in the tested meat products represent a risk to health. The consumption of inadequately cooked products and/or subjected to cross-contamination with other foods may lead to occurrence of foodborne diseases.

As Enfermidades Transmitidas por Alimentos representam um crescente e relevante problema de saúde pública. Além do prejuízo social, a contaminação de alimentos com microrganismos patogênicos gera um enorme prejuízo econômico. Técnicas de Análise de Risco permitem mensurar de forma mais adequada o impacto dos microrganismos contaminantes de alimentos na saúde da população. Uma Análise de Riscos, associada a uma combinação patógeno-alimento, envolve três passos: avaliação do risco, gestão do risco e comunicação do risco. Uma das etapas da avaliação do risco é a avaliação da exposição, baseada em dados sobre freqüência e nível de contaminação dos alimentos pelo patógeno avaliado no alimento em questão, o nível atingido pelo patógeno no momento do consumo e os padrões de consumo. Os produtos cárneos são os principais alimentos responsáveis pela veiculação de patógenos ao homem e os microrganismos de maior relevância nestes produtos são Listeria monocytogenes, Salmonella spp., Campylobacter spp. e Escherichia coli produtora de toxina de Shiga. O objetivo do presente estudo foi levantar informações qualitativas e quantitativas desses quatro patógenos em produtos cárneos (salsicha bovina, lingüiça suína, carne bovina moída e coxa de frango) comercializados no município de São Paulo, de forma a contribuir com dados para futuras avaliações de risco em relação a estes microrganismos nestes produtos. Das 552 amostras de produtos cárneos analisadas, L. monocytogenes foi o patógeno isolado com maior freqüência, sendo detectado em 48,7% das amostras, seguido por Campylobacter spp. em 6,0% e Salmonella spp. em 5,8%. E. coli produtora de toxina de Shiga não foi detectada em nenhuma das amostras estudadas. Listeria monocytogenes foi detectada em todos os tipos de produtos cárneos estudados, com freqüências mais elevadas nas amostras de carne bovina moída (59,4%), seguido de coxa de frango (58,0%), lingüiça suína (39,8%) e salsicha bovina (37,7%). Na maioria das amostras (94,4%), as contagens de L. monocytogenes foram inferiores a 102 UFC/g. As cepas de L. monocytogenes apresentaram ampla distribuição, sendo detectados os quatro grupos de sorotipos: 28,7% pertenceram ao Grupo 1 (sorotipos 1/2a e 3a), 21,0% ao Grupo 2 (sorotipos 1/2c e 3c), 17,0% ao Grupo 3 (sorotipos 1/2b, 3b e 7) e 13,8% ao Grupo 4 (sorotipos 4b, 4d e 4e). Salmonella spp. foi detectada em 32 amostras, sendo 20 (14,5%) de lingüiça e 12 (10,6%) de coxa de frango. As contagens foram baixas, variando de 3,0 a 9,3x10 NMP/g e os sorovares mais freqüentemente isolados foram S. Typhimurium (28,1%), S. Enteritidis (12,5%), S. Derby (12,5%) e S. I 4,[5],12:i:- (12,5%). Campylobacter spp. foi detectado em 33 amostras (6,0%), sendo 27 de coxa de frango (19,6%) e seis amostras de carne moída (4,3%). A presença de L. monocytogenes, Salmonella spp. e Campylobacter spp. nos produtos cárneos analisados representa um risco à saúde da população. O consumo destes produtos quando submetidos à cocção inadequada e/ou a contaminação cruzada com outros alimentos pode levar a ocorrência de Enfermidades Transmitidas por Alimentos. / Foodborne Diseases represent an increasingly important public health problem. Besides the social losses, contamination of food with pathogenic microorganisms generates an enormous economic damage. A more accurate measurement of the impact of microorganisms in food health can be achieved using Risk Analysis techniques. A risk analysis is composed by three elements: risk assessment, risk management and risk communication. One of the four steps of a risk assessment is the exposure assessment, based on data on frequency and level of contamination of a food by the pathogen under evaluation, levels of the pathogen in the food at the time of consumption and consumption patterns. Meat products are the main vehicles of pathogens to humans, where Listeria monocytogenes, Salmonella spp., Campylobacter spp. and Shiga toxin-producing Escherichia coli are the most relevant pathogens. The aim of this study was to obtain qualitative and quantitative information on these four pathogens in four types of meat products (beef sausage, pork sausage, ground beef and chicken leg) marketed in the city of Sao Paulo in order to contribute with data for future risk assessments for these microorganisms in these products. L. monocytogenes is the most frequent pathogen in the 552 samples of meat products analyzed, being detected in 48.7% of the samples, followed by Campylobacter spp. 6.0% and Salmonella spp. 5.8%. Shiga toxin-producing E. coli was not detected in any sample. L. monocytogenes was detected in all types of meat products, with highest frequency in ground beef (59.4%), followed by chicken leg (58.0%), pork sausage (39.8%) and beef sausage (37.7%). In most samples (94.4%), the counts of L. monocytogenes were below 102 CFU/g. L. monocytogenes strains were widely distributed in the four groups of serotypes: 28.7% belonged to Group 1 (serotypes 1/2a and 3a), 21% to Group 2 (serotypes 1/2c and 3c), 17% to Group 3 (serotypes 1/2b, 3b and 7) and 13.8% to Group 4 (serotypes 4b, 4d and 4e). Salmonella spp. was detected in 32 samples, being 20 (14.5%) of pork sausage and 12 (10.6%) of chicken leg. The counts were low, ranging from 3.0 to 9.3 x 10 MPN/g and the most frequent serovars were S. Typhimurium (28.1%), S. Enteritidis (12.5%), S. Derby (12.5%) and S. I 4, [5], 12: i: - (12.5%). Campylobacter spp. was detected in 33 samples (6.0%), being 27 of chicken leg (19.6%) and six samples of ground beef (4.3%). The presence of L. monocytogenes, Salmonella spp. and Campylobacter spp. in the tested meat products represent a risk to health. The consumption of inadequately cooked products and/or subjected to cross-contamination with other foods may lead to occurrence of foodborne diseases.

Orientador: Tomomasa Yano / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-23T11:52:53Z (GMT). No. of bitstreams: 1 Bernedo-Navarro_RobertAlvin_D.pdf: 2646572 bytes, checksum: 02b50bc28d5be6cddb78abfe621a047c (MD5) Previous issue date: 2013 / Resumo: Escherichia coli produtora de toxina de Shiga (STEC) é um grupo de importantes patógenos para humanos. Essas bactérias são relacionadas a várias doenças, como por exemplo, Síndrome Urêmica Hemolítica e produzem potentes toxinas denominadas toxinas de Shiga. Essas toxinas, tanto Stx1 quanto Stx2, compartilham um receptor celular comum, a globotriaosilceramida (Gb3) e exibem a mesma atividade biológica intracelular. O desenvolvimento de novos agentes neutralizantes dos danos induzidos por Stx pode representar uma estratégia promissora para o tratamento das doenças causadas por STEC em humanos. No presente estudo, nós desenvolvemos peptídeos sintéticos que exibem atividade neutralizante contra a citotoxicidade induzida por Stx tanto in vitro quanto in vivo e, além disso, que se ligam eficientemente ao receptor Gb3. O peptídeo P12-26 compete eficientemente com Stx2 para a ligação ao Gb3 in vitro. Além disso, os peptídeos PC7-12, P12-26 e PC7-30 inibiram a citotoxicidade de Stx1 e Stx2 em células Vero. Nós observamos que o peptídeo PC7-30 em forma de loop e o peptídeo P12-26 que é linear produziram as maiores porcentagens de inibição de Stx1 e Stx2 em células Vero, respectivamente. No entanto, o peptídeo P12-26 não inibiu a letalidade em camundongos, enquanto que o peptídeo PC7-30 inibiu a letalidade causada pela toxina Stx1. Nossos resultados indicam que os peptídeos P12-26 e PC7-30 são candidatos promissores para o desenvolvimento de agentes terapêuticos contra as doenças em seres humanos causadas por STEC / Abstract: Shiga toxin-producing Escherichia coli strains are important pathogens for humans. These bacteria are linked with severe diseases such as hemolytic uremic syndrome and produce potent known as Shiga toxins. These toxins, Stx1 and Stx2, share a common cellular receptor called globotriaosylceramide (Gb3) and exhibit the same intracellular biological activity. The development of new neutralizing agents for Stx-induced damage may represent a promising strategy for the treatment of diseases caused by STEC infections. In this study, we developed synthetic peptides that exhibit neutralizing activity against Stxinduced cytotoxicity both in vitro and in vivo and that bind efficiently to the Gb3 receptor. The peptide P12-26 competed efficiently with Stx2 for binding to Gb3 in vitro. Moreover, the peptides PC7-12, P12-26 and PC7-30 inhibited the cytotoxicity of Stx1 and Stx2 in Vero cells. We observed that the loop-constrained peptide PC7-30 and linear peptide P12-26 produced higher percentages of inhibition of Stx1 and Stx2 in Vero cells, respectively. However, the peptide P12-26 did not inhibit lethality in mice, whereas the loopconstrained peptide PC7-30 inhibited the lethality caused by Stx1. Our results indicate that the peptides P12-26 and PC7-30 are promising candidates for the development of therapeutic agents against diseases caused by STEC in humans / Doutorado / Bioquimica / Doutor em Biologia Funcional e Molecular

Low water activity foods (LWAF), specifically nuts and dried fruits, have been generally considered safe because they do not support the growth of foodborne pathogens. However, many pathogens have been noted to survive in LWAF for considerable periods of time, and a number of recent outbreaks and recalls have implicated various types of nuts and dried fruits. The Food Safety Modernization Act requires food processors to develop preventive control plans that make ready-to-eat LWAF safer for consumers. The presented research was designed to investigate several aspects of LWAF safety by evaluating a steam process as a strategy to remove pathogen contamination from LWAF, modeling the inactivation of such treatments, and studying the thermal resistances of two E. coli strains in low-water activity solutions. Low-temperature, vacuum-assisted steam (vacuum-steam) was evaluated as a potential intervention and preventive control to remove pathogens from the surface of LWAF without using high-heat treatments that could damage product quality. The presented work examined the efficacy of vacuum-steam (<85°C) as a means to decontaminate the surface of whole macadamia nuts, dried apricot halves, and raisins from Salmonella spp., Listeria monocytogenes, and Shiga toxin-producing Escherichia coli (STEC) contamination. The low-temperature steam treatments successfully reduced all pathogens by >4 log CFU/g from the surfaces of the foods. Additionally, Pediococcus acidilactici, proved to be a surrogate organism for these pathogens and could be used to challenge and validate similar treatments within processing plants. The data were fit to models, which showed that food type significantly impacted the fit, with the Weibull model best describing bacterial inactivation kinetics on raisins and macadamia nuts, and the Gompertz model best describing reductions on the apricot halves. The models were challenged for validation of their abilities to predict times required for 3-log reductions using internal and external datasets, determining the usefulness to industry members who wish to design similar thermal treatments for LWAF. Comparing predicted values from internally constructed models to observed values generated from external data, models were shown to be limited in scope and application and could only be applied to pathogen inactivation on different LWAF or thermal processes in certain circumstances. First-order and Weibull model predictions of bacterial reductions on dried apricots had varied success in predicting times for 3-log reductions on other thermally treated LWAF. However, the models of bacterial reductions on thermally treated macadamia nuts frequently overestimated the times required for 3-log bacterial reductions for other LWAF. In an effort to understand the effect that reduced water activity has specifically on STEC, two strains were investigated for induced thermal resistance due to osmotic stress. Thermal resistance of STEC strains (O121:H19 and O157:H7) were evaluated on the basis of strain variation, culture preparation, and water activity (D- and z-values). At the lowest treatment temperature (56°C), O121 displayed greater heat resistance than O157, and the broth-grown samples exhibited greater heat resistance than the lawn-grown cells, but significant differences were not observed at higher temperatures. Samples in reduced-water activity solutions displayed reduced thermal resistance at 56°C, but the z-values were 29-43% higher than those of high-water activity samples. While water activity has been shown to impact thermal resistance of pathogens, comparisons of STEC thermal resistance according to the D- and z-values revealed that other factors also play roles in pathogen thermal resistance on LWAF. Results from the collection of experiments conclude that efficacy of thermal treatments is impacted by the physiological state of the cells, stress experienced in the food matrix, and characteristics of the food, including water activity and composition. / Doctor of Philosophy / Consumers expect foods they purchase to be safe to consume by themselves and family members, particularly those that are ready-to-eat with no additional cooking requirements. Many of these foods are low-water activity foods (LWAF), like nuts and dried fruits, with very little water content that could be used by bacteria. These foods may be preferred snack foods due to their affordability, long shelf lives, and health benefits over other types of snack foods. Until recently, LWAF were generally considered safe because they do not support the growth of foodborne pathogens due to the lack of moisture or water within the food. However, a number of recent outbreaks related to various types of nuts and dried fruits have proven that many pathogens can survive in dried foods, even if not actively growing, for considerable amounts of time. Designed to address these types of food safety issues, the Food Safety Modernization Act recognizes risks associated with foods and responded with regulations requiring food processors to take steps to make ready-to-eat LWAF, like nuts and dried fruits, safer for consumers. A popular strategy is to treat foods with heat to destroy pathogens, however the quality attributes of some nuts and dried fruits could be damaged by high-heat treatments like roasting. An alternative process uses a vacuum to form steam at lower temperatures, allowing for efficient heat transfer through water droplets to the surface of the foods, thus causing less damage to the foods without introducing too much moisture. This research evaluated how this process could be used by food processors to remove harmful bacteria from the surfaces of whole macadamia nuts, dried apricot halves, and raisins. Results indicated that the low-temperature steam treatments successfully reduced Salmonella, Listeria monocytogenes, and Shiga toxin-producing Escherichia coli (STEC) by >4 log CFU/g (>99.99%) from the surfaces of the foods. Additionally, a nonpathogenic lactic acid bacterium, Pediococcus acidilactici, exhibited similar or greater heat tolerance, which would allow food processors to use it as a substitute, or surrogate, for in-plant studies without introducing harmful bacteria into the food processing environment. Mathematical models were used to describe the trends of bacterial death due to the steam treatments, and the results indicated that the type of food significantly impacted the reduction of bacteria. The models were tested using additional data collected within our own laboratory, as well as others. Results indicated that some of the models could be used as predictors of bacterial death for similar LWAF but can only be applied with caution and consideration for the type of food and process. Additionally, two different E. coli strains associated with outbreaks (O121:H19 and O157:H7) were investigated to understand impacts of strain variation, growth method, and water activity on thermal resistance. Some differences in heat resistance were observed between the strains and between the growth methods. Additionally, the reduced water activity seemed to decrease the bacteria's ability to withstand some heat treatments. Overall, thermal resistance studies indicated that several factors, in addition to water activity, impact pathogens' development of resistance to heat treatments. The experiments' results show that there are complex relationships between bacteria and the food they inhabit. Food processors must consider these relationships in order to design the best thermal processes to make LWAF safe for consumers.

Hemolytic uremic syndrome (HUS) induced by Shiga toxin-producing E. coli (STEC) is the most common causes of acute kidney injury in children. The therapy of the disease is symptomatic and the main factors leading to the development of severe course of a STEC-HUS are still unknown. In our study, we dealt with factors leading to development of a severe course of STEC-HUS in pediatric patients on both the host and pathogen side. Using retrospective analysis of the courses in children in the Czech Republic, we found that the most common cause of STEC-HUS was serotype O26 and HUS most often affected children under 3 years of age. 63,8 % required dialysis and mortality was 8.62 %. On the host side we focused on the relationship between the activation of the alternative complement pathway and the severity of the course of HUS. We found a significant difference in the level of the C3 part of complement in patients who required dialysis and patients for whom dialysis was not necessary. We also a cut-off value for the C3 part of complement and its reduction below 0.825 g / l was associated with the need for dialysis treatment and a higher incidence of extrarenal complications. Based not only on our results, it can be assumed that the therapeutic effect of complement could affect the severity of the disease....