Corrigenda pasted onto back end-papers. Bibliography: leaves 163-182. Analyses the proteins involved in Shigella flexneri O-antigen biosynthesis at the molecular level in order to gain a more concise understanding of the biosynthesis machinery and how it functions.

No Brasil existem poucos relatos sobre casos de Shigelose, um fator que contribui com o pouco conhecimento a respeito dessa doença. Além disso, a falta de obrigatoriedade por parte da legislação vigente em relação à pesquisa de Shigella tem contribuído com este fato. O presente trabalho teve por objetivo isolar, identificar e caracterizar isolados de Shigella envolvidas em surtos alimentares ocorridos no Rio Grande do Sul, além de comparar tais isolados de alimentos com amostras isoladas de fezes de pacientes com diarréia envolvidos nesses surtos. Após a identificação, os isolados foram submetidos à caracterização por suscetibilidade a antimicrobianos e PCR-Ribotipificação. Entre agosto de 2007 e agosto de 2008, foram isoladas três linhagens de Shigella (2 S. flexneri e 1 S. sonnei) a partir de placas de meio de cultura utilizadas pela FEPPS/LACEN/RS para pesquisa de Salmonella em alimentos suspeitos. Uma vez que a análise foi considerada negativa para a presença Salmonella, o resultado nas estatísticas epidemiológicas do RS possivelmente foi expresso como "agente do surto não identificado". Das 149 linhagens de Shigella isoladas pelo mesmo órgão, entre 2003 e 2007, 71,14 % foram identificados como S. flexneri, 21,48% como S. sonnei, 0,67% como S. dysenteriae e 6,71% foram classificados apenas como Shigella sp. Os resultados também demonstraram um aumento no percentual de isolados de S. sonnei, que em 2003 era nulo e em 2007 foi de 43,48 %, ao mesmo tempo o percentual de isolados de S. flexneri passou de 100% em 2003 para 47,83% em 2007. Em relação ao teste de resistência a antimicrobianos os isolados provenientes de fezes (n=149) demonstraram altas percentagens de resistência, sendo que as maiores foram observadas contra estreptomicina (88,59%), ampicilina (84,56%) e sulfametoxazol-trimetoprim (80,53%). Os maiores percentuais de sensibilidade foram para ciprofloxacina (96,64%), ácido nalidíxico (89,26%) e gentamicina (83,22 %). A resistência múltipla foi verificada em 90,19% dos isolados. Dos 73 perfis de resistência encontrados, 82,23 % apresentaram resistência a pelo menos três antimicrobianos. Seis perfis agruparam mais de quatro isolados (A, B, C, D, E e F). O mais resistente dos isolados de alimentos apresentou resistência à gentamicina e resistência intermediária à tetraciclina e ao cloranfenicol. Quando os isolados de Shigella foram submetidos à PCR-Ribotipificação, somente três perfis (SH1, SH2 e SH3) foram identificados. O perfil SH1 agrupou 76,31% dos isolados (todos S. flexneri) e o perfil SH2 agrupou 23% dos isolados (todos S. sonnei). De acordo com os resultados, várias linhagens de Shigella apresentaram o mesmo padrão de bandas na PCR-Ribotipificação e também o mesmo perfil de resistência, sugerindo tratar-se da mesma linhagem de Shigella; Os resultados obtidos no presente estudo indicam a necessidade do monitoramento contínuo da resistência da Shigella e também que a PCRRibotipificação pode ser útil na investigação de surtos de Shigeloses alimentares. / In Brazil, there are few reports about foodborne Shigellosis and the Brazilian regulation do no requires compulsory investigation for Shigella in foods, contributing to the lack of knowledge about this disease. The objective of the present study was to isolate, identify and characterize isolates of Shigella involved in outbreaks occurred in Rio Grande do Sul (RS), Southern Brazil, and compare the strains isolated from foods with those isolated from fecal stools of foodborne shigellosis victims. Food isolates were sampled between August 2007 and August 2008 from plates of selective medium used for Salmonella detection in suspect foods analysed by official Laboratory of RS (FEPPS/LACEN/RS), while fecal isolates were isolated from victim stools analysed between 2003 and 2007 by the same Laboratory. Bacterial samples were identified by FEPPS/LACEN/RS and submitted to antimicrobial susceptibility testing and PCR-Ribotyping. Results indicated that three Shigella (1 S. sonnei and 2 S. flexneri) were isolated from foods and 149 were isolated from fecal stools (71.14 % S. flexneri, 21.48 % S. sonnei, 0.67 % S. dysenteriae, and 6.71 % Shigella sp.). Results also showed an increase on the isolation percentage of S. sonnei from fecal samples, which was zero in 2003 increasing to 43.48 % in 2007. At the same period, the percentage of isolation of S. flexneri decreased from 100 % in 2003 to 47.83 % in 2007. Fecal stool isolates demonstrated high percentages of resistance, mainly for streptomycin (88.59 %), ampicillin (84.56 %) and sulfamethoxazole-trimethoprim (80.53 %). The highest percentage of sensitivity was observed for ciprofloxacin (96.64 %), nalidixic acid (89.26%) and gentamicin (83.22 %). Multiple resistance was observed in 137 isolates (90.19 %). Experiments revealed that 73 resistance patterns were found, and 82.23 % of the isolates showed resistance to at least three drugs. Six patterns grouped more than four isolates (A, B, C, D, E, and F). The most resistant isolates from foods showed only resistance to gentamicin and intermediate resistance to tetracycline and to chloramphenicol. PCR-Ribotyping identified three banding patterns (SH1, SH2, and SH3). The profile SH1 grouped 76.31 % of the isolates (all S. Flexneri) and profile SH2 grouped 23 % of isolates (all S. sonnei). According to the results, various Shigella isolates showed the same PCR-Ribotyping banding patterns and also the same resistance profile, suggesting it is the same strain of Shigella. The results indicate the need for continuous monitoring of resistance of Shigella and that the PCR-Ribotyping could be useful in the investigation of foodborne Shigellosis.

No Brasil existem poucos relatos sobre casos de Shigelose, um fator que contribui com o pouco conhecimento a respeito dessa doença. Além disso, a falta de obrigatoriedade por parte da legislação vigente em relação à pesquisa de Shigella tem contribuído com este fato. O presente trabalho teve por objetivo isolar, identificar e caracterizar isolados de Shigella envolvidas em surtos alimentares ocorridos no Rio Grande do Sul, além de comparar tais isolados de alimentos com amostras isoladas de fezes de pacientes com diarréia envolvidos nesses surtos. Após a identificação, os isolados foram submetidos à caracterização por suscetibilidade a antimicrobianos e PCR-Ribotipificação. Entre agosto de 2007 e agosto de 2008, foram isoladas três linhagens de Shigella (2 S. flexneri e 1 S. sonnei) a partir de placas de meio de cultura utilizadas pela FEPPS/LACEN/RS para pesquisa de Salmonella em alimentos suspeitos. Uma vez que a análise foi considerada negativa para a presença Salmonella, o resultado nas estatísticas epidemiológicas do RS possivelmente foi expresso como "agente do surto não identificado". Das 149 linhagens de Shigella isoladas pelo mesmo órgão, entre 2003 e 2007, 71,14 % foram identificados como S. flexneri, 21,48% como S. sonnei, 0,67% como S. dysenteriae e 6,71% foram classificados apenas como Shigella sp. Os resultados também demonstraram um aumento no percentual de isolados de S. sonnei, que em 2003 era nulo e em 2007 foi de 43,48 %, ao mesmo tempo o percentual de isolados de S. flexneri passou de 100% em 2003 para 47,83% em 2007. Em relação ao teste de resistência a antimicrobianos os isolados provenientes de fezes (n=149) demonstraram altas percentagens de resistência, sendo que as maiores foram observadas contra estreptomicina (88,59%), ampicilina (84,56%) e sulfametoxazol-trimetoprim (80,53%). Os maiores percentuais de sensibilidade foram para ciprofloxacina (96,64%), ácido nalidíxico (89,26%) e gentamicina (83,22 %). A resistência múltipla foi verificada em 90,19% dos isolados. Dos 73 perfis de resistência encontrados, 82,23 % apresentaram resistência a pelo menos três antimicrobianos. Seis perfis agruparam mais de quatro isolados (A, B, C, D, E e F). O mais resistente dos isolados de alimentos apresentou resistência à gentamicina e resistência intermediária à tetraciclina e ao cloranfenicol. Quando os isolados de Shigella foram submetidos à PCR-Ribotipificação, somente três perfis (SH1, SH2 e SH3) foram identificados. O perfil SH1 agrupou 76,31% dos isolados (todos S. flexneri) e o perfil SH2 agrupou 23% dos isolados (todos S. sonnei). De acordo com os resultados, várias linhagens de Shigella apresentaram o mesmo padrão de bandas na PCR-Ribotipificação e também o mesmo perfil de resistência, sugerindo tratar-se da mesma linhagem de Shigella; Os resultados obtidos no presente estudo indicam a necessidade do monitoramento contínuo da resistência da Shigella e também que a PCRRibotipificação pode ser útil na investigação de surtos de Shigeloses alimentares. / In Brazil, there are few reports about foodborne Shigellosis and the Brazilian regulation do no requires compulsory investigation for Shigella in foods, contributing to the lack of knowledge about this disease. The objective of the present study was to isolate, identify and characterize isolates of Shigella involved in outbreaks occurred in Rio Grande do Sul (RS), Southern Brazil, and compare the strains isolated from foods with those isolated from fecal stools of foodborne shigellosis victims. Food isolates were sampled between August 2007 and August 2008 from plates of selective medium used for Salmonella detection in suspect foods analysed by official Laboratory of RS (FEPPS/LACEN/RS), while fecal isolates were isolated from victim stools analysed between 2003 and 2007 by the same Laboratory. Bacterial samples were identified by FEPPS/LACEN/RS and submitted to antimicrobial susceptibility testing and PCR-Ribotyping. Results indicated that three Shigella (1 S. sonnei and 2 S. flexneri) were isolated from foods and 149 were isolated from fecal stools (71.14 % S. flexneri, 21.48 % S. sonnei, 0.67 % S. dysenteriae, and 6.71 % Shigella sp.). Results also showed an increase on the isolation percentage of S. sonnei from fecal samples, which was zero in 2003 increasing to 43.48 % in 2007. At the same period, the percentage of isolation of S. flexneri decreased from 100 % in 2003 to 47.83 % in 2007. Fecal stool isolates demonstrated high percentages of resistance, mainly for streptomycin (88.59 %), ampicillin (84.56 %) and sulfamethoxazole-trimethoprim (80.53 %). The highest percentage of sensitivity was observed for ciprofloxacin (96.64 %), nalidixic acid (89.26%) and gentamicin (83.22 %). Multiple resistance was observed in 137 isolates (90.19 %). Experiments revealed that 73 resistance patterns were found, and 82.23 % of the isolates showed resistance to at least three drugs. Six patterns grouped more than four isolates (A, B, C, D, E, and F). The most resistant isolates from foods showed only resistance to gentamicin and intermediate resistance to tetracycline and to chloramphenicol. PCR-Ribotyping identified three banding patterns (SH1, SH2, and SH3). The profile SH1 grouped 76.31 % of the isolates (all S. Flexneri) and profile SH2 grouped 23 % of isolates (all S. sonnei). According to the results, various Shigella isolates showed the same PCR-Ribotyping banding patterns and also the same resistance profile, suggesting it is the same strain of Shigella. The results indicate the need for continuous monitoring of resistance of Shigella and that the PCR-Ribotyping could be useful in the investigation of foodborne Shigellosis.

Submitted by ROBERTH NASCIMENTO DA TRINDADE null (octuberman@gmail.com) on 2016-02-02T12:22:18Z No. of bitstreams: 1 ROBERTH TRINDADE - Exploração racional da rizosfera de Senna spectabilis - interações entre as bactérias Pseudoxanthomonas indica e Shigella sp..pdf: 2399531 bytes, checksum: 1d992c19e1d2db2f229774b0f45cc074 (MD5) / Approved for entry into archive by Sandra Manzano de Almeida (smanzano@marilia.unesp.br) on 2016-02-03T17:44:59Z (GMT) No. of bitstreams: 1 trindade_rn_me_araiq_par.pdf: 740045 bytes, checksum: 46f1e680a7415dd924948bb180d6dfc7 (MD5) / Made available in DSpace on 2016-02-03T17:44:59Z (GMT). No. of bitstreams: 1 trindade_rn_me_araiq_par.pdf: 740045 bytes, checksum: 46f1e680a7415dd924948bb180d6dfc7 (MD5) Previous issue date: 2016-01-22 / O descobrimento de novas moléculas bioativas tem sido o grande alvo ao decorrer dos anos da química dos produtos naturais, particularmente, micro-organismos tem se evidenciado como uma importante fonte do descobrimento de novos fármacos. Uma ampla gama de compostos provenientes de organismos microbianos são relatados na literatura, porém, recentes pesquisas demonstram que tais micro-organismos podem sofrer indução por determinados agentes externos, químicos ou físicos, através de mecanismos de defesa ou até mesmo o mutualismo existente em determinado meio, produzindo novas estruturas químicas, que até então, tinham sua rota biosintética silenciada devido a metodologias padrões de cultivo isolado. Através de utilização de culturas mistas de bactérias, o presente trabalho proporciona o conhecimento da relação existente entre Pseudoxanthomonas indica e Shigella sp., ambas provenientes da rizosfera de Senna spectabilis. Para isso, as bactérias foram cultivadas em meio de cultivo líquido czapek broth, sendo realizado o estudo do crescimento das bactérias e produção de metabolitos frente ao tempo, tendo em vista uma maximização de resultados e maior indução de compostos químicos. A utilização de ferramentas analíticas de análise rápida e eficiente como a cromatografia líquida de alta eficiência (HPLC) associada à espectrometria de massas de alta resolução (HRMS) propiciaram a obtenção do perfil cromatográfico dos micro-organismos estudados em cultura mista e simples, sendo possível observar a existência de compostos químicos produzidos apenas em co-cultura, evidenciado o potencial existente da abordagem utilizada. / The discovery of new bioactive molecules has been the big target to over the years the chemistry of natural products, particularly micro-organisms has been shown to be an important source of discovery of new drugs. A wide range of compounds from microbial organisms are reported in the literature, however, recent research shows that these micro-organisms can undergo induction by certain external, chemical or physical agents, through defense mechanisms or even the existing mutualism on a particular medium, producing new chemical structures, which until then had silenced their biosynthetic route due to methodologies patterns of isolated farming. Through use of mixed cultures of bacteria, this study provides knowledge of the relationship between Pseudoxanthomonas indica and Shigella sp., Both from the rhizosphere of Senna spectabilis. For this, bacteria were grown in liquid Czapek broth cultivation being conducted the study of the growth of bacteria and production of metabolites against time, with a view to maximizing results and greater induction of chemical compounds. The use of analytics quickly and efficiently analyzes such as high-performance liquid chromatography tools (HPLC) associated with high resolution mass spectrometry (HRMS) enabled the obtaining of the chromatographic profile of microorganisms studied in mixed and single culture, and you can to observe the existence of chemical compounds produced only in co-culture demonstrated the potential of the approach used.

No Brasil existem poucos relatos sobre casos de Shigelose, um fator que contribui com o pouco conhecimento a respeito dessa doença. Além disso, a falta de obrigatoriedade por parte da legislação vigente em relação à pesquisa de Shigella tem contribuído com este fato. O presente trabalho teve por objetivo isolar, identificar e caracterizar isolados de Shigella envolvidas em surtos alimentares ocorridos no Rio Grande do Sul, além de comparar tais isolados de alimentos com amostras isoladas de fezes de pacientes com diarréia envolvidos nesses surtos. Após a identificação, os isolados foram submetidos à caracterização por suscetibilidade a antimicrobianos e PCR-Ribotipificação. Entre agosto de 2007 e agosto de 2008, foram isoladas três linhagens de Shigella (2 S. flexneri e 1 S. sonnei) a partir de placas de meio de cultura utilizadas pela FEPPS/LACEN/RS para pesquisa de Salmonella em alimentos suspeitos. Uma vez que a análise foi considerada negativa para a presença Salmonella, o resultado nas estatísticas epidemiológicas do RS possivelmente foi expresso como "agente do surto não identificado". Das 149 linhagens de Shigella isoladas pelo mesmo órgão, entre 2003 e 2007, 71,14 % foram identificados como S. flexneri, 21,48% como S. sonnei, 0,67% como S. dysenteriae e 6,71% foram classificados apenas como Shigella sp. Os resultados também demonstraram um aumento no percentual de isolados de S. sonnei, que em 2003 era nulo e em 2007 foi de 43,48 %, ao mesmo tempo o percentual de isolados de S. flexneri passou de 100% em 2003 para 47,83% em 2007. Em relação ao teste de resistência a antimicrobianos os isolados provenientes de fezes (n=149) demonstraram altas percentagens de resistência, sendo que as maiores foram observadas contra estreptomicina (88,59%), ampicilina (84,56%) e sulfametoxazol-trimetoprim (80,53%). Os maiores percentuais de sensibilidade foram para ciprofloxacina (96,64%), ácido nalidíxico (89,26%) e gentamicina (83,22 %). A resistência múltipla foi verificada em 90,19% dos isolados. Dos 73 perfis de resistência encontrados, 82,23 % apresentaram resistência a pelo menos três antimicrobianos. Seis perfis agruparam mais de quatro isolados (A, B, C, D, E e F). O mais resistente dos isolados de alimentos apresentou resistência à gentamicina e resistência intermediária à tetraciclina e ao cloranfenicol. Quando os isolados de Shigella foram submetidos à PCR-Ribotipificação, somente três perfis (SH1, SH2 e SH3) foram identificados. O perfil SH1 agrupou 76,31% dos isolados (todos S. flexneri) e o perfil SH2 agrupou 23% dos isolados (todos S. sonnei). De acordo com os resultados, várias linhagens de Shigella apresentaram o mesmo padrão de bandas na PCR-Ribotipificação e também o mesmo perfil de resistência, sugerindo tratar-se da mesma linhagem de Shigella; Os resultados obtidos no presente estudo indicam a necessidade do monitoramento contínuo da resistência da Shigella e também que a PCRRibotipificação pode ser útil na investigação de surtos de Shigeloses alimentares. / In Brazil, there are few reports about foodborne Shigellosis and the Brazilian regulation do no requires compulsory investigation for Shigella in foods, contributing to the lack of knowledge about this disease. The objective of the present study was to isolate, identify and characterize isolates of Shigella involved in outbreaks occurred in Rio Grande do Sul (RS), Southern Brazil, and compare the strains isolated from foods with those isolated from fecal stools of foodborne shigellosis victims. Food isolates were sampled between August 2007 and August 2008 from plates of selective medium used for Salmonella detection in suspect foods analysed by official Laboratory of RS (FEPPS/LACEN/RS), while fecal isolates were isolated from victim stools analysed between 2003 and 2007 by the same Laboratory. Bacterial samples were identified by FEPPS/LACEN/RS and submitted to antimicrobial susceptibility testing and PCR-Ribotyping. Results indicated that three Shigella (1 S. sonnei and 2 S. flexneri) were isolated from foods and 149 were isolated from fecal stools (71.14 % S. flexneri, 21.48 % S. sonnei, 0.67 % S. dysenteriae, and 6.71 % Shigella sp.). Results also showed an increase on the isolation percentage of S. sonnei from fecal samples, which was zero in 2003 increasing to 43.48 % in 2007. At the same period, the percentage of isolation of S. flexneri decreased from 100 % in 2003 to 47.83 % in 2007. Fecal stool isolates demonstrated high percentages of resistance, mainly for streptomycin (88.59 %), ampicillin (84.56 %) and sulfamethoxazole-trimethoprim (80.53 %). The highest percentage of sensitivity was observed for ciprofloxacin (96.64 %), nalidixic acid (89.26%) and gentamicin (83.22 %). Multiple resistance was observed in 137 isolates (90.19 %). Experiments revealed that 73 resistance patterns were found, and 82.23 % of the isolates showed resistance to at least three drugs. Six patterns grouped more than four isolates (A, B, C, D, E, and F). The most resistant isolates from foods showed only resistance to gentamicin and intermediate resistance to tetracycline and to chloramphenicol. PCR-Ribotyping identified three banding patterns (SH1, SH2, and SH3). The profile SH1 grouped 76.31 % of the isolates (all S. Flexneri) and profile SH2 grouped 23 % of isolates (all S. sonnei). According to the results, various Shigella isolates showed the same PCR-Ribotyping banding patterns and also the same resistance profile, suggesting it is the same strain of Shigella. The results indicate the need for continuous monitoring of resistance of Shigella and that the PCR-Ribotyping could be useful in the investigation of foodborne Shigellosis.

Shigella est une bactérie pathogène à Gram-négatif qui cause la shigellose ou dysenterie bacillaire. Cette maladie est une cause importante de morbidité chez les jeunes enfants et les adultes dans les pays en développement, avec presqu’un million de morts par an. Jusqu'à ce jour, aucun vaccin efficace contre Shigella n’est disponible et la prévalence croissante de souches multirésistantes fait de Shigella une menace importante en termes de santé publique. La virulence de Shigella est médiée par la sécrétion d'un arsenal de protéines (effecteurs) capables d'interférer avec diverses voies de signalisations de la cellule hôte. La sécrétion de effecteurs dépend d'un système de sécrétion de type 3 (SST3), véritable aiguille moléculaire assemblée à la surface bactérienne permettant l’injection les protéines de virulence dans le cytoplasme de la cellule hôte. Le SST3 est assemblé à 37 °C et est composé de trois parties distinctes: i) un bulbe cytoplasmique, ii) un corps basal et ii) une aiguille extracellulaire. Cette dernière est constituée de l’assemblage d’une centaine de copies de la protéine MxiH pour la partie extracellulaire et de plusieurs copies de la protéine MxiI pour la partie périplasmique. Avant le contact cellulaire, le SST3 est maintenu dans un état "OFF" d’une part, par un complexe de protéines (IpaD et IpaB) localisé au sommet de l’aiguille et, d’autre part par une protéine (MxiC) probablement située à la base du SST3 via son interaction avec MxiI. Suite au contact cellulaire, le SST3 est activé et permet la sécrétion d’IpaC, protéine hydrophobe formant, avec IpaB, un pore dans la membrane de la cellule hôte pour permettre la translocation des effecteurs. Suite à la détection du contact cellulaire par le complexe d’extrémité (IpaB et IpaD), un signal est transmit jusqu’à la base de l’aiguille afin d’activer la sécrétion de MxiC et finalement celle des effecteurs. Des études mutationnelles ont montré que la transmission du signal d'activation du haut vers la base de l’aiguille implique les sous-unités de l’aiguille MxiH et MxiI. Ce signal permet la dissociation de MxiC et MxiI et donc la libération des effecteurs. Dans ce travail, nous avons caractérisé le rôle de MxiI dans la transmission du signal d'activation de la sécrétion via une série de mutations dirigées et aléatoires et déterminé le domaine responsable de son interaction avec MxiC. D'autre part, nous avons mis en évidence un lien entre la sécrétion de MxiC par le SST3 et celle d'un effecteur, IcsB. IcsB nécessite une protéine chaperon, IpgA, pour sa stabilité et sa sécrétion. Une fois sécrétée, elle joue différentes fonctions dans la cellule hôte et notamment, permet l’échappement de Shigella à l’autophagie. Dans ce travail, nous avons montré que IcsB est capable de lier le cholestérol et que cette liaison est nécessaire pour l’échappement de de la bactérie à l’autophagie. Nous avons montré, en utilisant des approches biochimiques, qu’IcsB pourrait avoir une activité de type cystéine protéase via une diade catalytique conservée (C306 et H145). Nous avons identifié de nouveaux partenaires d'interaction d’IcsB, tels que OspB et VirA, ce qui pourrait permettre de mieux comprendre la fonction d’IcsB dans la cellule. En conclusion, ce travail a permis de mieux comprendre le mécanisme d'activation du SS T3 ainsi que la fonction de l'effecteur IcsB dans la virulence de Shigella. / Doctorat en Sciences biomédicales et pharmaceutiques (Médecine) / info:eu-repo/semantics/nonPublished

Vibrio cholerae y Shigella dysenteriae, entre otras bacterias enteropatógenas, causan enfermedades gastrointestinales, la segunda causa de muerte en niños menores de cinco años en el mundo. Los sucesos de gastroenteritis que desencadenan dichos microorganismos son mediados por la acción molecular de toxinas secretadas de tipo AB, CTX y STX, respectivamente para V, cholerae y S, dysenteriae. Dichas toxinas causan desbalances iónicos y lisis celular, generando deshidratación, pérdida de electrolitos y nutrientes. El correcto funcionamiento de ambas toxinas requiere una relación estricta de cinco subunidades de la proteína B por cada subunidad A, sin embargo, los mecanismos moleculares que regulan la expresión y mantienen la relación 5:1 entre las subunidades son poco entendidos. El objetivo de este estudio es analizar la regulación post transcripcional de las toxinas CTX y STX mediante aproximaciones experimentales in vitro y usando reacciones libres de células, en un entorno altamente puro y controlado. Nuestros resultados in vitro indican que CTX se expresa de manera más eficiente que STX. En el caso de CTX, la subunidad B tuvo mayor expresión que A, con una relación cercana a 5:1 como visto en estudios previos realizados in vivo. Por el contrario, STX fue sintetizada con baja eficiencia independientemente de la presencia o ausencia de la región codificantes para STXA, desviándose notablemente de una relación activa de 5 B por cada subunidad A. La adición de ppGpp, molécula implicada en la respuesta al estrés en bacterias, resultó en una ligera disminución de la expresión de ambas toxinas. En conclusión, nuestros resultados indican que la relación de 5 a 1 entre B y A de las toxinas CTX de V. cholerae es regulada durante la síntesis de proteínas. Por el contrario, la ausencia de regulación a nivel transcripcional o traduccional de STX del presente estudio in vitro, fue también observada en estudios in vivo, indicando que en la célula existen otros factores que podrían modular la estequiometría de síntesis. Si bien ambas toxinas, CTX y STX, permanecen a la misma familia de exotoxinas, los resultados del presente estudio indican que la regulación de su expresión difiere ampliamente entre ellas. Los resultados aquí reportados brindan nuevas perspectivas para el desarrollo de moléculas inhibidoras, con especial énfasis en perturbar el ribosoma de V, cholerae, para un desbalance en la síntesis de la toxina CTX y así reducir la patogenicidad de la bacteria. / Vibrio cholerae and Shigella dysenteriae, among other enteropathogenic bacteria, cause gastrointestinal diseases, the second cause of death in children under five years of age in the world. The events of gastroenteritis that trigger these microorganisms are mediated by the molecular action of secreted toxins of type AB, CTX and STX, respectively for V. cholerae and S. dysenteriae. These toxins cause ionic imbalances and cell lysis, generating dehydration, loss of electrolytes and nutrients. The correct functioning of both toxins requires a strict relationship of five subunits of protein B for each subunit A, however, the molecular mechanisms that regulate expression and maintain the 5: 1 ratio between the subunits are poorly understood. The objective of this study is to analyze the post transcriptional regulation of CTX and STX toxins by in vitro experimental approaches and using cell-free reactions, in a highly pure and controlled environment. Our in vitro results indicate that CTX is expressed more efficiently than STX. In the case of CTX, subunit B had greater expression than A, with a ratio close to 5: 1 as seen in previous studies conducted in vivo. In contrast, STX was synthesized with low efficiency regardless of the presence or absence of the region coding for STXA, deviating markedly from an active ratio of 5 B for each subunit A. The addition of ppGpp, a molecule involved in the stress response in bacteria, resulted in a slight decrease in the expression of both toxins. In conclusion, our results indicate that the ratio of 5 to 1 between B and A of CTX toxins of V. cholerae is regulated during protein synthesis. On the contrary, the absence of transcriptional or transcriptional STX regulation of the present in vitro study was also observed in in vivo studies, indicating that the cell may harbor other factors that could modulate the synthesis stoichiometry. Although both toxins, CTX and STX, belong to the same family of exotoxins, the results of the present study indicate that the regulation of their expression differs widely. The results reported here provide new perspectives for the development of inhibitory molecules, with special emphasis on disturbing the ribosome of V. cholerae, to provoke an imbalance in the synthesis of CTX toxin and thus to reduce the pathogenicity of the bacteria. / Tesis

Please read the abstract in the section, 00front, of this document / Dissertation (MSc)--University of Pretoria, 2001. / Microbiology and Plant Pathology / MSc / unrestricted

Enteropathogenic bacteria, such as Shigella and Salmonella, are associated with diarrheal diseases, which remain a significant cause of infant mortality worldwide. The secretion of protein effectors by the type III secretion apparatus (T3SA) is used by these pathogens to invade human cells and modulate host cell functions. First, we used RNA-Seq to analyze the differential transcriptome of Shigella flexneri when the T3SA is active or inactive. This allowed us to identify two uncharacterized genes that were temporarily named gem1 and gem3 and whose expression was regulated by MxiE and IpgC as other late substrates of the T3SA. Finally, we pursued the characterization of gem1 and gem3 at the protein level and renamed them icaT and icaR, respectively, when we found their protein products were secreted by the T3SA. Furthermore, we find homologs of icaT and icaR with a conserved MxiE box in several E. coli phylogroups. We also demonstrated that these homologous genes could be reactivated when both MxiE and IpgC were introduced in these strains. This discovery paved a new perspective on the evolution of pathogenesis into the E. coli lineage as both commensal and pathogenic strains harbored these genes. Treating infections caused by Enterobacteriaceae is becoming more challenging due to growing antibiotic resistance and no vaccines are widely available. Accordingly, the World Health Organization (WHO) recognized that we entered the "post-antibiotic era," where new antibiotics or antivirulence drugs are urgently needed, including for Shigella. The T3SA is an attractive target for antivirulence drugs, which may become alternative to classical antibiotics. Through screening 3,000 compounds, we found two novel inhibitors of the T3SA. Our data suggested that one of these candidate inhibitors, a dipyridyl-containing compound, reduces the virulence of Shigella at the transcriptional level. Indeed, the virulence inhibition occurs via the repression of the transcriptional activator VirB by the small chromosomal RNA RyhB, which is upregulated by this compound through an unknown mechanism involving the pyridyl groups. The repression of VirB induced by this molecule reduce the expression of several genes encoding parts of the T3SA. In comparison, the second compound is a quinone that seems to affect the assembly of the T3SA.

Problem: Shigella is a gram-negative enteropathogen that, when passed through fecal particles from one host to the oral cavity of another host, causes an infectious disease known as shigellosis. One of the distinctive features of the infection by Shigella is its ability to bypass its host’s autophagic defenses. It does this through the use of a Type III secretion system, found in gram-negative pathogens like Shigella, which injects virulent proteins into the host cell. One of these proteins is IcsB; however, its exact function is not well understood. This study aims to better understand the role of this protein in the infection. Methods: A yeast two-hybrid screening test is used in this case to examine the interactions between variations of the protein IcsB, and a library of host proteins. Given IcsB’s high yeast toxicity and that resulted in the total absence of yeast colony formation, the first aim was to identify IcsB variants which expression would not prevent yeast growth. The second aim was to use the mutant with reduced cytotoxicity to perform a Y2H screen that will allow for the identification of candidate host proteins interacting with IcsB. Results: Two mutations of the IcsB protein grew in the Y2HG yeast strain, indicating a significant reduction in the protein’s toxicity. Of the cultures that reacted, high stringency and strong interaction was observed between four genes and IcsB proteins. Among the four identified clones that grew, three corresponded to the gene RNF2, while the last one corresponds to a non-coding sequence. Key control experiments revealed that the interaction of IcsB with RNF2 is likely false-positive. Thus, when screened full-length IcsB using new epithelial cells cDNAVI libraries, strong interaction was observed between three genes and our IcsB proteins. All the three genes DDX3X, FANCL, and SGT1 passed the false-positive interaction tests. It is interesting to notice that DDX3X and SGT1 interacted with catalytically active and inactive IcsB, suggesting that the interactions established between IcsB and prey proteins does not require the catalytic - C306A mutation and that IcsB most likely does not function as a protease against these two proteins. By contrast, FANCL bound catalytically inactive, but not catalytically active IcsB, suggesting it could be a substrate of IcsB. The literature provides some support for the putative role of DDX3X, FANCL, and SGT1 in regulating the vacuole escape of Shigella through IcsB action. Conclusion: The aim of this study was to determine the functional of IcsB in the vacuole escape of Shigella. This study successfully identified three candidates interacting partner proteins for IcsB. Key control experiments confirmed the interaction of IcsB with DDX3X, FANCL and SGT1. This study provides a basis for further research, with further study aimed at confirming these results during Shigella infection