Les séquences d'insertion sont des parasites moléculaires d'ADN codant uniquement pour leur machinerie de transposition et sont retrouvées majoritairement dans les génomes et les plasmides des procaryotes. Le séquençage génomique massif de la dernière décennie nous a permis de détecter chez des souches bactériennes cliniques plusieurs gènes de résistance aux antibiotiques associés aux séquences d'insertion sous forme de transposons composés. Il a été suggéré que les séquences d'insertion jouent un rôle prépondérant dans l'évolution bactérienne et qu'elles possèdent un pouvoir recruteur permettant de sélectionner, réorganiser et propager des gènes conférant un avantage sélectif à l'hôte. Nous avons partiellement caractérisé le potentiel recruteur de deux séquences d'insertion associées à des gènes de résistance, la séquence IS26 de Proteus vulgaris et la séquence ISJO de Salmonella typhimurium, en observant les étapes de recrutement d'un gène chromosomique et leurs distributions épidémiologiques en consultant les banques de données. / Insertion sequences are DNA molecular parasites encoding exclusively their transposition function, and are mainly found within the genomes and plasmids of prokaryotic organisms. The massive genomic sequencing we have witnessed in the last decade has allowed us to detect in clinical bacterial isolates many antibiotic resistance genes associated with insertion sequences in the form of composite transposons. It has been suggested that insertion sequences may act as a primary modulator of bacterial evolution, and that they possess a recruitment capacity allowing them to select, reorganize and spread genes encoding adaptation functions for their hosts. We have partially characterized the recruitment potential of two insertion sequences well known for their association with antibiotic resistance genes, IS10 from Salmonella typhimurium and 1S26 from Proteus vulgaris, by observing the steps involved in the recruitment process of a chromosomal gene and their epidemiological distribution by consulting various databanks.

In the twenty-first century, advances in synthetic biology and molecular tools to implement programmable behavior into microbes have fueled significant efforts to develop microbial-based therapeutics. Bacteria and viruses have been explored independently for their ability to replicate and induce cytotoxic effects in cancer cells selectively. This dissertation aims to co-opt the anti-tumor capabilities of gram-negative Salmonella enterica subspecies enterica serotype Typhimurium (referred to as Salmonella typhimurium moving forward) and picornaviruses (small RNA viruses with positive sense genomes) to develop a potent, single bacterial-viral consortium- based system to treat solid tumors.I first describe our efforts to co-opt S. typhimurium’s natural internalization into hosts and intracellular space-sensing to deliver self-amplifying picornaviral RNA. Protein effectors that promote intracellular survival of S. typhimurium within the Salmonella-Containing-Vacuole (SCV) are transcribed by Salmonella Pathogenicity Island-2 (SPI-2) promoters, which turn on after sensing the intracellular pH, ion concentrations, and oxidative stressors. These effectors are then translocated into the host’s cytoplasm by a needle apparatus that connects the SCV and cytoplasm, which is also transcribed by SPI-2 promoters. By using the SPI-2 promoter PsseA to drive the expression of fluorescent reporters and membrane-disrupting proteins (eukaryotic and prokaryotic), efficient escape of Salmonella-produced proteins into tumor-host cells was established. RNA delivery into host cells was also made possible by a secondary SPI-2 promoter, PsseJ, which transcribes RNA polymerase T7 (T7), which then transcribes a T7-promoter-driven Poliovirus replicon or full-length Senecavirus A (SVA). Inoculation of this engineered S. typhimurium strain on a panel of cancer cell lines identified the system’s ability to deliver viral replicons and full-length viruses in a small cell cancer cell line, H446. In a murine model, S. typhimurium delivery of SVA was then shown to clear xenografted H446 tumors. Motivated by the possibility of delivering other picornaviral species with similar anti-tumor properties, but documented healthy tissue cytotoxicity, S. typhimurium was further engineered to control SVA viral spread. By driving Tobacco Etch Virus (TEV) protease expression via a second SseA promoter, and replacing a natural cleavage site on SVA with the TEV-cleavage domain, we demonstrate TEV-dependent SVA spread in H446 cells. I conclude with efforts on engineering TEV-dependent-SVA transgene expression to confer greater antitumor properties. Interferon-gamma and granulocyte-macrophage colony-stimulating factor (GM-CSF) have been reported to attenuate H446 growth in vitro. Expression of interferon-gamma off SVA would produce a direct selective pressure against viral replication and virion production. However, a fusion of human GM-CSF to Nano-Luciferase protein on the TEV-dependent SVA genome maintained luminescent signals, GM-CSF activity, and TEV-dependent spread, providing a framework to survey anti-tumor properties of SVA-transgenes. Furthermore, I address our development of syngeneic models for Salmonella-mediated delivery of SVA, an important step towards clinical applications of the system as immunocompetent models more closely correlate to immunocompetent patient populations. SVA’s efficient entry and replication in neuroendocrine-derived tissue identified murine neuroblastoma N1E-115 cells as a suitable cell line for SVA cytotoxicity studies. However, the ability of these cells to support bacterial-viral superinfections is unknown. Here, we show that Salmonella-mediated launch of SVA leads to viral spread that can attenuate heterologous hind flank tumor growth and improve their survival along with mice engrafted with orthotopic intracranial brain tumors.

La pollution engendrée par les pratiques d'élevage constitue une préoccupation majeure dans beaucoup de pays. Il a été notamment démontré que les fèces animales logent des pathogènes potentiellement nocifs, dont le Escherichia coli 0157:H7 et des espèces du genre Salmonella. Ainsi, le recyclage des résidus organiques qui n'ont pas été préalablement soumis à un traitement adéquat pose un risque élevé de contamination de l'environnement, du sol et des eaux souterraines. L'élimination des pathogènes par les techniques de biopasteurisation s'avère un moyen prometteur pour la gestion des résidus animaux et en particulier du fumier solide. Bien que chacune des techniques existantes possèdent des avantages, il y a toutefois toujours place à l'amélioration. Dans cette étude, nous avons présenté un nouveau système de traitement en continu par biopasteurisation appelé SHOCMD (Système d'Hygiénisation en Oxygénation Contrôlée), et son efficacité à éliminer les bactéries pathogènes. Les résultats ont été comparés à ceux d'un système conventionnel, soit la cellule de compostage à aération forcée. Afin de vérifier l'efficacité du SHOCMD , deux pathogènes majeurs, soit E, coli 0157:H7 et Salmonella enterica subsp. enterica serovar Typhimurium, ont été introduits dans le fumier solide de porc. À la fin du traitement, les échantillons ont été analysés en utilisant des techniques microbiologiques et moléculaires. De plus, la diversité bactérienne, un paramètre important pour une gestion efficace de la biopasteurisation, a été déterminée à l'aide de techniques moléculaire. Les résultats ont démontré que le SHOCMD est un système efficace pour l'hygiénisation du fumier solide et que le produit final répond aux normes de sécurité concernant les pathogènes. / Pollution by livestock wastes has become a great concern in many countries. It is well documented that potentially harmful pathogens including Escherichia coli 0157:117 and Salmonella spp. are shed in animal feces. Recycling of these wastes without treatment poses a risk of contamination of the environment, soil and groundwater. Bio-pasteurization is a promising technique for management of solid animal wastes especially manure. However, even if each method has its own advantages there is still room for improvement. In this study, we present a new bio-pasteurization system called SHOCIM (Système d'Hygiénisation en Oxygénation Contrôlée) and the efficiency of the SHOCIM to eliminate pathogens was compared to the Cell, which is one of the conventional Systems. To evaluate the efficiency of SHOC™, two majors pathogens, E. coli 0157:H7 and Salmonella enterica subsp. enterica serovar Typhimurium were introduced in manure. At the end of treatment, the samples were analyzed with both microbiological and molecular techniques. Bacterial diversity which is important in the effective management of biopasteurization process was monitored by molecular techniques as well. Results demonstrated that SHOCIM is an efficient facility for manure treatment and the final product meet the standards for pathogens safety.

Au cours de ce travail, différents glucosylamines et aminodésoxyglucoses ont été synthétisés et caractérisés par différentes méthodes spectroscopiques dont l’IRTF, la RMN 1H, 13C et MALDI-Tof MS. L’étude des propriétés biologiques de ces molécules réalisée, d’une part, avec deux champignons du bois, Coriolus versicolor et Poria placenta, et d’autre part, avec trois microorganismes potentiellement rencontrés dans des aliments, Listeria innocua, Salmonella typhimurium et Fusarium proliferatum ont indiqué une contribution positive de la N-alkylation, du degré de N-substitution et de la quaternisation sur l’inhibition de leur croissance. Par ailleurs, l’impact sur la bioactivité, de la position du groupe amine sur le sucre, a été étudié. Il a été montré que la position du groupe amine sur le C-1 du glucose conduisait à une activité antifongique contre C. versicolor et P. placenta plus prononcée alors que la position C-3 du glucose était favorable à une activité antimicrobienne contre L. innocua et S. typhimurium. / In this study different glucosylamines and amino desoxyglucoses were synthesized and characterised using various spectroscopic methods including IRFT, both 1H and 13C NMR spectroscopy and MALDI-Tof MS. Biological assessment of these compounds realised with two wood decay fungi, Coriolus versicolor and Poria placenta on one hand, and with three food microorganisms Listeria innocua, Salmonella typhimurium and Fusarium proliferatum on other hand, indicated a positive impact of both N-alkylation and degree of N-substitution and quaternisation on their growth inhibition. Furthermore, a biological impact of the amine position on sugar was studied. It was found that amine function attached to the C-1 of glucose conducted to the best antifungal activity against both C. versicolor and P. placenta while that fixed on the C-3 of glucose was indicated for antibacterial activity against L. innocua and S. typhimurium.

Salmonella spp. é reconhecida como uma das bactérias que mais causam doenças de origem alimentar no mundo. Dentre as diversas sorovariedades de Salmonella, a Typhimurium é uma das sorovariedades de maior ocorrência no mundo. Várias metodologias de tipagem fenotípicas e genotípicas foram desenvolvidas com o intuito de se delinear a epidemiologia e diversidade genotípica de Salmonella Typhimurium. Entretanto, a tipagem fenotípica é muitas vezes limitada por sua baixa capacidade de diferenciação de subtipos pertencentes a uma mesma sorovariedade de Salmonella, um problema minimizado pelos métodos genotípicos. No Brasil, foram realizados poucos estudos que genotiparam linhagens de S. Typhimurium. Os objetivos deste estudo foram caracterizar linhagens de S. Typhimurium isoladas de humanos, alimentos, animais e ambiente do animal no Brasil quanto ao seu potencial patogênico, perfil de resistência a antimicrobianos e diversidade genotípica. Foram estudadas 119 linhagens de S. Typhimurium, isoladas de material clínico de humanos (43), alimentos diversos (49), material clínico de suínos (22) e do ambiente de suínos (5), entre 1983 e 2013, provenientes de várias Estados do Brasil. A presença de 12 genes de virulência foi pesquisada por PCR. O perfil de resistência a 13 antimicrobianos foi realizado pelo método de discodifusão. A tipagem molecular foi realizada por Pulsed-field gel electrophoresis (PFGE), Enterobacterial repetitive intergenic consensus PCR (ERIC-PCR), Multiple-locus variablenumber tandem-repeats analysis (MLVA), Clustered regularly interspaced short palindromic repeats - Multi-virulence locus sequence typing (CRISPR-MVLST), Multilocus sequence typing (MLST) e sequenciamento do genoma completo para 92 linhagens de S. Typhimurium isoladas de humanos (43) e alimentos (46). As metodologias PFGE, ERIC-PCR e MLVA foram realizadas para 70 linhagens de S. Typhimurium isoladas de humanos (43), animais (22) e ambiente do animal (5). Todas as 119 linhagens apresentaram os genes sipA, flgK, flgL e invA. O gene sipD e o gene sopE2 foram encontrados em 118 (99,2%) linhagens. O gene fljB foi encontrado em 117 (98,3%) linhagens. O gene sopD foi presente em 114 (95,8%) linhagens, o gene sopB em 111 (93,3%) linhagens, o gene ssaR em 102 (85,7%) linhagens, o gene sifA em 86 (72,3%) linhagens e 45 (37,8%) linhagens apresentaram o gene plasmidial spvB. De um total de 119 linhagens, 64 (62,2%) linhagens foram resistentes a pelo menos um dos 13 antimicrobianos testados, sendo que 36 (30,3%) linhagens foram multi-droga resistentes (MDR). Na comparação dos isolados de humanos e alimentos, as linhagens isoladas de humanos antes de meados 1990, ficaram alocadas nos grupos PFGE-A, PFGE-B1, PFGE-B2, ERIC-A, ERIC-B, MLVA-A, MLVA-B1, MLVA-B2 e G1, G2, H para CRISPRMVLST. As linhagens isoladas de humanos após esse período ficaram alocadas nos grupos PFGE-B1, ERIC-A, MLVA-B1, MLVA-B2 e G2. As linhagens isoladas de alimentos ficaram alocadas nos grupos PFGE-A, PFGE-B1, ERIC-A, ERIC-B, MLVA-A, MLVA-B1, MLVAB2, G1 e G2. Por MLST, do total de 92 linhagens isoladas de humanos e alimentos, 77 linhagens foram tipadas como ST19. Pelo sequenciamento do genoma completo, as linhagens isoladas de alimentos e humanos ficaram alocadas no grupos I e J independente das datas de isolamento. Na comparação dos isolados de humanos e animais, as linhagens das duas origens ficaram alocadas nos grupos PFGE-D1, PFGE-D2, ERIC-C1, MLVA-C1 e MLVA-D. ii Conclui-se que a grande prevalência de genes de virulência nas linhagens de S. Typhimurium estudadas reforça o potencial das mesmas causarem doenças em humanos, bem como, os riscos de sua presença em alimentos, animais para consumo humano e ambiente. A ocorrência de S. Typhimurium multi-droga resistentes isoladas de alimentos diversos e de suínos para consumo é um alerta para o possível risco de humanos ingerirem alimentos contaminados por tais linhagens. Em conjunto os resultados de PFGE, ERIC-PCR, MLVA, CRISPR-MVLST sugerem que as linhagens de S. Typhimurium isoladas de humanos eram geneticamente mais diversificadas antes de meados de 1990, o que pode sugerir a seleção de um subtipo de S. Typhimurium mais adaptado, depois que Salmonella Enteritidis tornou-se a sorovariedade de maior ocorrência no Brasil após esse período. Com relação às linhagens isoladas de alimentos, os resultados de PFGE, ERIC-PCR, MLVA e CRISPR-MVLST sugerem que durante o período estudado houve a circulação de mais de um subtipo no país. Os resultados de MLST sugerem que tais linhagens tenham uma origem filogenética comum. Os resultados do sequenciamento do genoma completo sugerem que houve a circulação de mais de um subtipo de S. Typhimurium no país, com relação às linhagens de humanos e alimentos. Também alerta para o possível risco de linhagens MDR isoladas de alimentos contaminarem humanos e/ou disseminarem genes de resistência a antibióticos para linhagens de origem clínica e não clínica. Na comparação dos isolados de humanos e animais, os resultados de PFGE, ERICPCR e MLVA sugerem que algumas linhagens isoladas de suínos e humanos podem descender de um subtipo comum. Ademais, as linhagens MDR isoladas de suínos e do ambiente de suínos alertam para o possível risco de porcos usados para consumo contaminarem humanos, o ambiente e outros porcos. / Salmonella spp. is recognized as one of the most involved bacteria that cause food-borne diseases in the world. Among the various serovars of Salmonella, Typhimurium is one of the most frequent serovars worldwide. Several phenotypic and genotypic typing methods have been developed in order to delineate the epidemiology and genotypic diversity of Salmonella Typhimurium. However, phenotypic typing is often limited by its low capacity to differentiate subtypes belonging to the same serovar of Salmonella, a problem minimized by genotypic methods. In Brazil, few studies have been conducted that genotyped S. Typhimurium strains. The aims of this study were to characterize S. Typhimurium strains isolated from humans, food, animals and animal\'s environment in Brazil regarding its pathogenic potential, antimicrobial resistance and genotypic diversity. We studied 119 S. Typhimurium strains isolated from human clinical material (43), different foods (49), clinical material from pigs (22) and pigs environment (5), between 1983 and 2013 from various States of Brazil. The presence of 12 virulence genes was investigated by PCR. The resistance profile against 13 antimicrobial was performed by the disk diffusion method. Molecular typing was performed by Pulsed-field gel electrophoresis (PFGE), Enterobacterial repetitive intergenic consensus PCR (ERIC-PCR), Multiple-locus variable-number tandem-repeats analysis (MLVA), Clustered regularly interspaced short palindromic repeats - Multi-virulence locus sequence typing (CRISPR-MVLST), Multilocus sequence typing (MLST) and whole genome sequencing for 92 S. Typhimurium strains isolated from humans (43) and food (46). PFGE, ERIC-PCR and MLVA methods were performed for 70 S. Typhimurium strains isolated from humans (43), animals (22) and the animal\'s environment (5). All 119 strains showed the sipA, flgK, flgL and invA genes. The sipD and sopE2 genes were found in 118 (99.2%) strains. The fljB gene was found in 117 (98.3%) strains. The sopD gene was present in 114 (95.8%) strains, the gene sopB in 111 (93.3%) strains, the ssaR gene in 102 (85.7%) strains, the gene sifA in 86 (72.3%) strains and 45 (37.8%) strains showed the plasmid gene spvB. From a total of 119 strains, 64 (62.2%) strains were resistant to at least one of the 13 antimicrobials tested, and 36 (30.3%) strains were multi-drug resistant (MDR). In the comparison of isolates from humans and food, the strains isolated from humans before mid-1990s were allocated in PFGE-A, PFGE-B1, PFGE-B2, ERIC-A, ERIC-B, MLVA-A, MLVA-B1, MLVA-B2 and G1, G2, H for CRISPR-MVLST. The strains isolated from humans after this period were allocated in PFGE-B1, ERIC-A, MLVA-B1, MLVA-B2 and G2 clusters. The strains isolated from food were allocated in PFGE-A, PFGE-B1, ERIC-A, ERIC-B, MLVA-A, MLVA-B1, MLVA-B2, G1 and G2 clusters. By MLST, of the total of 92 strains isolated from humans and food, 77 strains were typed as ST19. By whole genome sequencing, the strains isolated from food and humans were allocated in I and J clusters independently of its isolation date. In the comparison of isolates from humans and animals, strains of the two origins were allocated in PFGE-D1, PFGE-D2, ERIC-C1, MLVA-C1 and MLVA-D clusters. In conclusion, the high frequency of virulence genes in the S. Typhimurium strains studied reinforces their potential hazard to cause disease in humans, as well as the risk of its presence in food, animals for human consumption and the environment. The occurrence of S. Typhimurium multi-drug iv resistant isolated from various food and pigs for consumption is an alert of the possible risk for humans to ingest contaminated food with those strains. Together the results of PFGE, ERIC-PCR, MLVA e CRISPR-MVLST suggest that S. Typhimurium strains isolated from humans were genetically more diverse before mid-1990s, which might indicate the selection of a more adapted S. Typhimurium subtype after Salmonella Enteritidis became the most prevalent serovar in Brazil. Regarding the strains isolated from food, the results of PFGE, ERIC-PCR, MLVA and CRISPR-MVLST suggest that during the studied period there was circulation of more than one subtype in the country. The MLST results suggest that these strains have a common phylogenetic origin. The results of the whole genome sequencing suggest that there may be more than one subtype circulating in the country, with respect to the strains of human and food origins. Also, alerts for the possible risk of MDR strains isolated from food to contaminate humans and/or disseminate antibiotic resistance genes for strains of clinical and non-clinical origin. In the comparison of isolates from humans and animals, the results of PFGE, ERIC-PCR and MLVA suggest that some strains isolated from pigs and humans may descend from a common subtype. In addition, the MDR strains isolated from pigs and pig environment warn for the possible risk of pigs used for human consumption to contaminate humans, the environment and other pigs.

La salmonelosis es considerada la enfermedad más grave que afecta a los cobayos, causando altas tasas de mortalidad y morbilidad, principalmente por los serovares Typhimurium y Enteritidis. Para que se lleve a cabo la infección, debe existir la expresión de diversos grupos de genes que permitan a la bacteria adherirse, multiplicarse y sobrevivir a las defensas del hospedero. El objetivo del estudio fue caracterizar molecularmente aislados de Salmonella enterica provenientes del cepario del Laboratorio de Microbiología y Parasitología de la Facultad de Medicina Veterinaria de la Universidad Nacional Mayor de San Marcos. Se utilizaron 80 aislados, 70 obtenidos de cobayos infectados naturalmente y cinco de clínicamente sanos, procedentes de granjas de producción intensiva ubicadas en Lima y Junín, Perú. Se utilizó la técnica de Reacción en Cadena de la Polimerasa (PCR) múltiple para la detección de genes invA, prot6E y fliC, correspondientes al género Salmonella, serovar Enteritidis y Typhimurium, respectivamente. También se detectaron los genes de virulencia tolC, sitC, spiA, sopB, lpfC, sifA, spvB, pefA y sipB, necesarios para producir la enfermedad. Finalmente, se evaluó la variabilidad genética mediante la técnica de ERIC-PCR utilizando los primers ERIC1R y ERIC2. Para evaluar la diversidad de los aislados, se realizó el análisis de agrupamiento para generar un dendrograma usando el programa bioinformático NTSYSpc 2.10, empleando el método UPGMA basado en el coeficiente de similaridad de DICE. Se identificó la serovariedad Typhimurium y los nueve genes de virulencia en el 100% de los aislados. La evaluación de los perfiles electroforéticos obtenidos por la técnica de ERIC-PCR demostró patrones de bandas de ADN similares con una homogeneidad mayor al 90%, lo que sugiere una dispersión clonal de los aislados. La presencia de cepas de Salmonella Typhimurium con una amplia variedad de genes de virulencia constituye un riesgo potencial para la producción de cobayos y una fuente de contaminación alimentaria o por contacto al humano. / Tesis

O presente trabalho objetivou identificar os fatores de risco para a presença de S. Enteritidis no sistema de produção de frangos de corte, avaliar, qualificar e quantificar as variáveis encontradas e elaborar um modelo teórico de estimativa de risco deste sorovar em frangos criados em sistema de integração. Os dados foram obtidos de trabalhos recentes realizados por alguns autores e deram subsídios à realização de uma análise de riscos microbiológicos. Para caracterização molecular foram utilizadas 42 cepas de Salmonella isoladas de frangos e rações inoculados experimentalmente com uma cepa de S. Typhimurium. A inoculação da bactéria foi realizada na ração e a mesma tratada com diferentes concentrações dos ácidos propílico, fórmico e acético sendo, então, fornecida para consumo ad libitum até os 21 dias de idade, quando as aves foram sacrificadas. Foram obtidos diferentes perfis genéticos com o uso do ERIC e BOX-PCR, que se mostraram eficientes para discriminação das cepas em estudo. / The aim of this work was identify the risk factors for S. Enteritidis in the production system of broiler chickens, to evaluate, qualify and quantify the variables studied and to make a theoretical model of risk assessment of this serovar in broilers in integration system. Therefore, the data was obtain from works of some authors and supported the proposed model of microbiological risk analysis. For molecular characterization were included 42 Salmonella spp. strains isolated from chicks and feed experimentally inoculated with S. Tiphimurium. After inoculation of feed with the specific dose of strain, it was submitted to treatment with propilic, formic and acetic acids in several concentrations and it was given to birds ad libitum until 21 days old, when they were sacrificed. It was obtained different patterns through the ERIC and BOX-PCR techniques, which showed good discrimination power for the strains analyzed.

Sterile ceramic plates and the surface of beef steaks were inoculated with the pathogenic microorganisms Listeria monocytogenes, Campylobacter jejuni, Escherichia coli and Salmonella typhimurium. Samples were also inoculated with nonpathogenic microorganisms Clostridium sporogenes ATCC 7955, Pseudomonas aeruginosa, and Bacillus stearothermophilus. Concentrations of organisms in the pure culture used to inoculate the samples were selected within the range of 106 to 108 colony forming units/ml (CFU/ml). Samples were treated with ultra-high temperature (UHT), and· the surviving organisms were recovered and counted. Meat samples were exposed to 1100°C for 22 seconds. Beef steaks inoculated with pathogenic microorganisms had low survival rates. The percent destruction ranged from 99.9 to 99.8. Sixteen percent of the spores from putrefactive anaerobe 3679 were destroyed. UHT was not found to be effective in destroying the spores of this organism. UHT destroyed 99.9 to 100 percent of the nonpathogenic microorganisms Pseudomonas and Bacillus stearothermophilus, respectively, inoculated on the surface of beef steaks prior to treatment. UHT pasteurization technology proved to be an effective method of controlling vegetative pathogens and vegetative spoilage organisms on meat surfaces.

Chapter: 1 Introduction Genus Salmonella is a Gram-negative rod shaped facultative anaerobic bacteria that can survive inside the host macrophages and cause persistent infection. Salmonella Typhimurium, Salmonella Typhi and Salmonella Enteritidis are the serovars, which belong to the Salmonella enterica species. S. Typhi causes typhoid fever in humans. S. Typhimurium is one of the important causes for food poisoning in humans. It causes typhoid like fever in mice and serves as a good model system to study Salmonella pathogenesis. Salmonella infection occurs via the orofecal route following which it invades the intestinal mucosa through several ways, namely by antigen sampling M cells, CD18+ macrophages present in the intestinal lumen or via a forced entry in the non phagocytic enterocytes. Upon entry Salmonella resides in an intracellular phagosomal compartment called the Salmonella containing vacuole (SCV). The SCV only transiently acquires endocytic markers like TfnR, EEA1, Rab4, Rab5, Rab11 and Rab7. It eventually uncouples from the endocytic pathway to avoid lysosomal fusion and ultimately reaches the golgi apparatus achieving a perinuclear position. The mechanisms by which phagocytes kill the virulent Salmonella are not completely understood, however the role of nicotinamide-adenine dinucleotide phosphate (NADPH) phagocytic oxidase system has been strongly implicated. The generation of reactive oxygen species (ROS) occurs via a membrane-bound flavocytochrome b558, consisting of two phagocytic oxidase components (gp91phox and p22phox) and four cytosolic components, p40phox, p47phox, p67phox, and a GTP-binding Rac protein. Further, professional phagocytes like macrophages generate nitric oxide (NO) that acts as a potent agent to limit the growth of many intracellular pathogens including Salmonella. Chapter:2 Resistance to host Nitrosative stress in Salmonella by quenching L-arginine. Arginine is a common substrate for both inducible nitric oxide synthase (iNOS) and arginase. The competition between iNOS and arginase for arginine contributes to the outcome of several parasitic and bacterial infections. Salmonella infection in macrophage cell line RAW264.7 induces iNOS. Because the availability of L-arginine is a major determinant for nitric oxide (NO) synthesis, we hypothesize that in the Salmonella infected macrophages NO production may be regulated by arginase. Here we report for the first time that Salmonella up-regulates arginase II but not arginase I isoform in RAW264.7 macrophages. Blocking arginase increases the substrate L-arginine availability to iNOS for production of more nitric oxide and perhaps peroxynitrite molecules in the infected cells allowing better killing of virulent Salmonella in a NO dependent manner. RAW264.7 macrophages treated with iNOS inhibitor aminoguanidine reverts the attenuation in arginase blocked condition. Further, the NO block created by Salmonella was removed by increasing concentration of L-arginine. In the whole-mice system arginase I, although constitutive, is much more abundant than the inducible arginase II isoform. Inhibition of arginase activity in mice during the course of Salmonella infection reduces the bacterial burden and delays the disease outcome in a NO dependent manner. Chapter:3 Hrg (hydrogen peroxide resistant gene), a LysR type transcriptional regulator confers resistance to oxidative stress in Salmonella LysR type transcriptional regulators are one of the key players that help bacteria adapt to different environments. We have christened STM0952, a putative LysR type transcriptional regulator in Salmonella enterica serovar Typhimurium as the hydrogen peroxide resistance gene (hrg). By generating a knock out of the hrg gene, we demonstrate that the hrg mutant serovar Typhimurium is sensitive to oxidative products of the respiratory burst, specifically to hydrogen peroxide. The hrg mutant is profoundly attenuated in the murine model of infection and shows decreased intracellular proliferation in macrophages. It was also found to induce increased amount of reactive oxygen species and co-localization with gp91phox in the macrophage cell line, when compared to the wild type. An overproducing strain of this gene showed a survival advantage over the wild type Salmonella under hydrogen peroxide induced stress condition. Microarray analysis suggested the presence of a Hrg regulon, which is required for resistance to the toxic oxidative products of the reticulo-endothelial system. Chapter:4 Importance of the host oxidative stress in antigen presentation and its modulation by Salmonella: Role of TLR Synthetic CpG containing oligodeoxynucleotide TLR-9 agonist (CpG ODN) activates innate immunity and can stimulate antigen presentation against numerous intracellular pathogens. We report that Salmonella Typhimurium growth can be inhibited by the CpG ODN treatment in the murine dendritic cells. This inhibitory effect was shown to be mediated by an increased reactive oxygen species (ROS) production. We further show that the CpG ODN treatment of the dendritic cells during Salmonella infection leads to a ROS dependent increased antigen presentation. In addition, TLR-9 signaling inhibitor was able to inhibit the CpG ODN mediated increased antigen presentation, ROS production and pathogen killing. These data indicate that CpG ODN can improve the ability of the murine dendritic cells to contain the growth of the virulent Salmonella through ROS dependent killing and could as well be used as an effective adjuvant in vaccines against Salmonella infection.

Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (leaves 207-232).