Le système de sécrétion de type VI (SST6) est un complexe multi-protéique permettant l’export d’effecteurs. Ce mécanisme est impliqué à la fois dans la virulence envers les cellules eucaryotes, dans l’activité antibactérienne mais également dans l’acquisition d’ions présents dans ’environnement. Ainsi, le SST6 joue un rôle important dans l’adaptation et la compétition, éléments essentiels dans la colonisation et la persistance au sein d’une niche écologique. Actuellement, très peu d’études portent sur l’importance du SST6 chez des souches environnementales, contrairement aux nombreuses études portant sur des pathogènes tels que Pseudomonas aeruginosa, Burkholderia thailandensis, Vibrio cholerae ou Escherichia coli. Mon sujet de recherche avait pour objectif de caractériser le ou les rôles du SST6 de la souche environnementale Pseudomonas fluorescens MFE01. Ces travaux ont permis d’appréhender certaines fonctions du SST6 de cette souche. Le génome de MFE01 ne comporte qu’un seul cluster de gènes du SST6 où sont regroupés les gènes codant pour la machinerie du SST6 (le « core-component ») à l’exception des gènes hcp. Les protéines Hcp sont des éléments structuraux du SST6 dont elles forment le tube interne qui permet le transfert des effecteurs. Différents gènes hcp sont disséminés sur le chromosome et parmi ces « hcp » orphelins, hcp2 et hcp3 codent respectivement pour les protéines Hcp2 et Hcp3. Ces deux Hcp sécrétées par le SST6, sont associées à l’activité antibactérienne de MFE01 sur différentes souches pathogènes et environnementales, tels que P. aeruginosa, P. fluorescens MFN1032 et Pectobacterium atrosepticum. La protéine Hcp1, codée par le gène orphelin hcp1, est impliquée dans l’inhibition de mobilité de souche compétitrice. Hcp1 permettrait la sécrétion d’au moins deux toxines qui perturberaient l’assemblage du flagelle. Chez MFE01Δhcp1 et MFE01ΔtssC (TssC est un élément de la gaine contractile du SST6), ces toxines seraient accumulées dans le cytoplasme, inhibant ainsi ’assemblage de leur propre flagelle. La surproduction du régulateur FliA, qui contrôle notamment l’assemblage du filament flagellaire, restaure la mobilité chez ces deux mutants. En parallèle, le SST6 de la souche MFE01 est essentiel à la formation et la maturation de biofilm mais également à la compétition bactérienne en biofilm mixte. Ce système interviendrait dans la communication bactérienne indispensable au comportement social, requis lors de l’élaboration des biofilms. / Type VI secretion system (T6SS) is a multiproteic apparatus that secreted proteinaceous effectors. T6SS participate in a variety of functions, whose eukaryote virulence, antibacterial activity or metal ion uptake. These capacities conferring an advantage in adaptation and competition, crucial to colonization or persistence within ecological niche. As well, only a few studies have focused on the T6SS functions of environmental strains, contrary to numerous studies dealing with pathogens as Pseudomonas aeruginosa, Burkholderia thailandensis, Vibrio cholerae or Escherichia coli. The purpose of my research project was to characterize the T6SS function(s) of the environmental strain Pseudomonas fluorescens MFE01. This work had led to understand the various functions of T6SS of MFE01 strain. This strain has a single T6SS cluster where all the core component proteins were gathered, except hcp genes. Three orphan hcp genes where found and are scattered in genome. Hcp proteins form the inner tube allowing effectors secretion. Both Hcp2 and Hcp3 proteins were involved in antibacterial activity on pathogens or environmental strains like P. aeruginosa, P. fluorescens or Pectobacterium atrosepticum. Characterization of Hcp1 proteins role constituted a major focus of this project. Hcp1 proteins participate to motility inhibition of competitive strains through T6SS. Hcp1 may be associated with secretion of at least two toxins perturbing the flagellar filament assembly. In MFE01Δhcp1 and MFE01ΔtssC mutants (Tss is a contractile sheath constituent), these toxins may be accumulated into cytoplasm and perturb assembly of their own flagella. Interestingly, overproduction of FliA flagellar regulator, which controls assembly of flagellar filament, restores motility of both mutants. Simultaneously, T6SS of MFE01 strain contributes to maturation and biofilm formation but also in bacterial competition within mixed biofilm. T6SS may be a mean of bacterial communication and thus coordinate a social behavior, primordial for biofilm formation.

No description available.

Aeromonas spp. são bastonetes Gram negativos amplamente distribuídos nos ambientes aquáticos, com relatos de isolamento em água de abastecimento público e alimentos. Este micro-organismo possui potencial de causar doenças intestinais e extraintestinais cuja patogenicidade está associada a sua virulência multifatorial. Diversos determinantes de virulência de Aeromonas já foram identificados, incluindo sistemas de secreção de proteínas. O sistema de secreção tipo VI (SST6) é o mais recente sistema de secreção de proteínas identificado em bactérias cuja presença em estirpes no gênero Aeromonas pode implicar atividades de citotoxicidade para o hospedeiro, pois esse sistema é capaz de injetar moléculas efetoras dentro da célula, interferindo diretamente nos processos celulares. A fim de determinar a presença e analisar a distribuição dos genes hcp e vgrG codificadores das proteínas efetoras do SST6 em Aeromonas spp. o presente estudo examinou 119 cepas isoladas de diversas origens pela técnica da PCR após o desenho de oligonucleotídeos iniciadores específicos. Objetivamos ainda analisar a variabilidade genética interespecífica dos genes hcp e vgrG a partir de dados de sequenciamento. Os resultados obtidos indicaram a distribuição dos genes vgrG e hcp em 46% das cepas de Aeromonas hydrophila e Aeromonas caviae de diferentes origens. Entre as cepas de A. hydrophila a maior frequência foi observada nas cepas isoladas de humanos, onde todas foram positivas para os iniciadores que amplificaram um produto de 541 pb do gene vgrG e 418 pb do gene hcp. Entre as cepas de A. caviae, a incidência de genes vgrG e hcp foi mais elevada nas cepas isoladas de alface (60%) e peixes (50%). As cepas analisadas de origem ambiental apresentaram índice total de 36% de positividade, apresentando frequência de 60% e 22% em A. hydrophila e A. caviae, respectivamente. Os dados obtidos da análise de cepas de origem alimentar mostraram a presença dos genes vgrG e hcp em 67% (A. hydrophila) e 60% (A. caviae) das cepas isoladas de folhas de alface. Nas cepas isoladas de queijo os genes foram encontrados em 67% e 12,5% das cepas de A. hydrophila e de A. caviae, respectivamente. O alinhamento múltiplo entre as sequências dos segmentos dos genes hcp e vgrG obtidas no sequenciamento indicou grau de identidade nucleotídica de 75 a 100% entre as sequências de hcp e 80 a 100% entre as sequências de vgrG. Em conclusão, nossos resultados indicaram que os iniciadores desenhados foram capazes de detectar suas sequências alvo em cepas de A. caviae e outras espécies de Aeromonas, sugerindo a existência de homologia entre os genes nas diferentes espécies, confirmada após sequenciamento de DNA. Os dados indicaram que esses genes estão distribuídos em várias espécies de Aeromonas e em cepas isoladas de diversas fontes. Ressaltamos a prevalência de cepas de A. hydrophila PCR-positivas em isolados clínicos, sugerindo a participação do SST6 no complexo universo da virulência multifatorial que permeia esse micro-organismo / Aeromonas species are Gram negative bacilli distributed widely in aquatic environments, with reports of isolation of this microorganism in water for public supply and food. Aeromonas have the potential to cause intestinal and extra intestinal infections whose pathogenicity is associated with multifactorial virulence. A number of virulence determinants have already been identified in Aeromonas, including protein secretion systems. The type VI secretion system (T6SS) is the most recent pathway to secrete proteins identified in bacteria. The presence of T6SS in Aeromonas strains may involve activities of cytotoxicity to the host, since this system is capable of injecting effectors molecules into the cell, interfering directly with a variety of cellular processes. The present study examined 119 strains of different origins by PCR, after the design of specific primers, to determine the distribution of vgrG and hcp genes encoding the effector proteins of T6SS in Aeromonas spp. We aimed to further analyze the interspecific sequence variation of hcp and vgrG genes based on sequencing data. The results show the presence of hcp and vgrG genes in 46% of A. hydrophila and A. caviae strains from different sources. All A. hydrophila strains isolated from humans were positive for the primers used to amplify a product of 541 bp and 418 bp of vgrG and hcp genes, respectively. Among A. caviae strains, the incidence of hcp and vgrG genes was high in the strains isolated from lettuce (60%) and fish (50%). The overall PCR-positive rate of strains from environmental source was 36%, with a frequency of 60% and 22% in A. hydrophila and A. caviae, respectively. The data obtained from analysis of food-borne strains showed the presence of hcp and vgrG genes in 67% (A. hydrophila) and 60% (A. caviae) of strains isolated from lettuce, while in the strains isolated from cheese the frequency was 67% (A. hydrophila) and 12.5% (A. caviae). The multiple alignment of hcp and vgrG sequences obtained revealed nucleotide identity rate between 75-100% among the hcp sequences and 80-100% in vgrG sequences. In conclusion, our results indicate that the primers designed were able to detect their target sequences in strains of A. caviae and other Aeromonas species, suggesting the existence of homology between genes in different species, as confirmed after DNA sequencing. The data indicate that these genes are distributed in various Aeromonas species from different sources. We emphasize the prevalence of PCR-positive A. hydrophila strains in clinical samples suggesting the involvement of T6SS in the complex universe of multifactorial virulence, which permeates this microorganism

Work presented in this thesis is in two parts. Part one: The X-ray crystal structures of potential antimicrobial drug targets. The protein IspF (2C-methyl-D-erythritol-2,4-cyclodiphosphate synthase, EC: 4.6.1.12) from two pathogens (Burkholderia cenocepacia and Plasmodium falciparum) has been investigated. IspF is an enzyme of isoprenoid-precursor biosynthesis and is considered to be a potential drug target. The results of structural and fragment-screening efforts presented here inform early stage drug discovery efforts. The structure of the PabC protein (4-amino-4-deoxychorismate lyase, EC: 4.1.3.38) from the Gram-negative pathogen Pseudomonas aeruginosa was also determined. PabC is involved in the production of para-aminobenzoic acid on the path to folate. Comparisons with previously solved PabC structures identified a spatially conserved tyrosine residue in the active site and suggest that a re-evaluation of a published mechanism is warranted. Part two: Immunity proteins in the Gram-negative Type VI secretion system. The X-ray crystal structures of the proteins Rap1a and Rap2a from Serratia marcescens, inhibitors of the peptidoglycan amidase toxins secreted by some Gram-negative bacteria employing the Type VI secretion pathway, were determined by molecular replacement and analysed.

Aeromonas spp. são bastonetes Gram negativos amplamente distribuídos nos ambientes aquáticos, com relatos de isolamento em água de abastecimento público e alimentos. Este micro-organismo possui potencial de causar doenças intestinais e extraintestinais cuja patogenicidade está associada a sua virulência multifatorial. Diversos determinantes de virulência de Aeromonas já foram identificados, incluindo sistemas de secreção de proteínas. O sistema de secreção tipo VI (SST6) é o mais recente sistema de secreção de proteínas identificado em bactérias cuja presença em estirpes no gênero Aeromonas pode implicar atividades de citotoxicidade para o hospedeiro, pois esse sistema é capaz de injetar moléculas efetoras dentro da célula, interferindo diretamente nos processos celulares. A fim de determinar a presença e analisar a distribuição dos genes hcp e vgrG codificadores das proteínas efetoras do SST6 em Aeromonas spp. o presente estudo examinou 119 cepas isoladas de diversas origens pela técnica da PCR após o desenho de oligonucleotídeos iniciadores específicos. Objetivamos ainda analisar a variabilidade genética interespecífica dos genes hcp e vgrG a partir de dados de sequenciamento. Os resultados obtidos indicaram a distribuição dos genes vgrG e hcp em 46% das cepas de Aeromonas hydrophila e Aeromonas caviae de diferentes origens. Entre as cepas de A. hydrophila a maior frequência foi observada nas cepas isoladas de humanos, onde todas foram positivas para os iniciadores que amplificaram um produto de 541 pb do gene vgrG e 418 pb do gene hcp. Entre as cepas de A. caviae, a incidência de genes vgrG e hcp foi mais elevada nas cepas isoladas de alface (60%) e peixes (50%). As cepas analisadas de origem ambiental apresentaram índice total de 36% de positividade, apresentando frequência de 60% e 22% em A. hydrophila e A. caviae, respectivamente. Os dados obtidos da análise de cepas de origem alimentar mostraram a presença dos genes vgrG e hcp em 67% (A. hydrophila) e 60% (A. caviae) das cepas isoladas de folhas de alface. Nas cepas isoladas de queijo os genes foram encontrados em 67% e 12,5% das cepas de A. hydrophila e de A. caviae, respectivamente. O alinhamento múltiplo entre as sequências dos segmentos dos genes hcp e vgrG obtidas no sequenciamento indicou grau de identidade nucleotídica de 75 a 100% entre as sequências de hcp e 80 a 100% entre as sequências de vgrG. Em conclusão, nossos resultados indicaram que os iniciadores desenhados foram capazes de detectar suas sequências alvo em cepas de A. caviae e outras espécies de Aeromonas, sugerindo a existência de homologia entre os genes nas diferentes espécies, confirmada após sequenciamento de DNA. Os dados indicaram que esses genes estão distribuídos em várias espécies de Aeromonas e em cepas isoladas de diversas fontes. Ressaltamos a prevalência de cepas de A. hydrophila PCR-positivas em isolados clínicos, sugerindo a participação do SST6 no complexo universo da virulência multifatorial que permeia esse micro-organismo / Aeromonas species are Gram negative bacilli distributed widely in aquatic environments, with reports of isolation of this microorganism in water for public supply and food. Aeromonas have the potential to cause intestinal and extra intestinal infections whose pathogenicity is associated with multifactorial virulence. A number of virulence determinants have already been identified in Aeromonas, including protein secretion systems. The type VI secretion system (T6SS) is the most recent pathway to secrete proteins identified in bacteria. The presence of T6SS in Aeromonas strains may involve activities of cytotoxicity to the host, since this system is capable of injecting effectors molecules into the cell, interfering directly with a variety of cellular processes. The present study examined 119 strains of different origins by PCR, after the design of specific primers, to determine the distribution of vgrG and hcp genes encoding the effector proteins of T6SS in Aeromonas spp. We aimed to further analyze the interspecific sequence variation of hcp and vgrG genes based on sequencing data. The results show the presence of hcp and vgrG genes in 46% of A. hydrophila and A. caviae strains from different sources. All A. hydrophila strains isolated from humans were positive for the primers used to amplify a product of 541 bp and 418 bp of vgrG and hcp genes, respectively. Among A. caviae strains, the incidence of hcp and vgrG genes was high in the strains isolated from lettuce (60%) and fish (50%). The overall PCR-positive rate of strains from environmental source was 36%, with a frequency of 60% and 22% in A. hydrophila and A. caviae, respectively. The data obtained from analysis of food-borne strains showed the presence of hcp and vgrG genes in 67% (A. hydrophila) and 60% (A. caviae) of strains isolated from lettuce, while in the strains isolated from cheese the frequency was 67% (A. hydrophila) and 12.5% (A. caviae). The multiple alignment of hcp and vgrG sequences obtained revealed nucleotide identity rate between 75-100% among the hcp sequences and 80-100% in vgrG sequences. In conclusion, our results indicate that the primers designed were able to detect their target sequences in strains of A. caviae and other Aeromonas species, suggesting the existence of homology between genes in different species, as confirmed after DNA sequencing. The data indicate that these genes are distributed in various Aeromonas species from different sources. We emphasize the prevalence of PCR-positive A. hydrophila strains in clinical samples suggesting the involvement of T6SS in the complex universe of multifactorial virulence, which permeates this microorganism

Les composés organiques hydrophobes (HOC), une grande famille de molécules naturelles ou d’origine anthropique incluant les lipides et les hydrocarbures, constituent une part significative de la matière organique dans les écosystèmes marins. Du fait de leur faible solubilité dans l’eau, les bactéries qui les dégradent requièrent la mise en place de fonctions cellulaires spécifiques permettant d’augmenter la fraction assimilable de ces HOC. La formation de biofilms à l’interface eau-HOC est une de ces stratégies adaptatives. C’est le cas pour Marinobacter hydrocarbonoclasticus SP17, modèle d’étude utilisé au laboratoire, qui est capable de former des biofilms sur un large spectre de HOC métabolisables tels que les alcanes, les triglycérides et les alcools gras. Le but de mes recherches consistait à améliorer la compréhension du processus d’adhésion et de développement des biofilms sur les HOC, à travers la caractérisation fonctionnelle de 10 gènes candidats mis en évidence lors d’analyses d’expression en protéomique et en transcriptomique. Pour mener à bien ce projet, des outils génétiques et une caractérisation fonctionnelle propre à chaque gène ont dû être développés. L’étude fonctionnelle du gène MARHY2686 a relevé son implication dans la formation de biofilm sur les alcanes. La co-expression de MARHY2686 et des gènes adjacents MARHY2687 et MARHY2685 en transcriptomique, leur distribution phylogénétique et leur conservation de la synthénie suggèreraient que ces trois gènes soient impliqués dans le même processus biologique. D’après l’identité forte de 36 % qui existe entre la protéine MARHY2686 et une protéine périplasmique AdeT d’un système de pompe d’efflux tripartite d’Acinetobacter baumanii, cette protéine, en association avec MARHY2687 et MARHY2685, pourrait faire partie d’un système de ce type. Par ailleurs, des observations ont permis d’envisager une implication potentielle de ce gène dans l’assimilation des HOC ou dans l’accumulation des réserves lipidiques intracellulaires. M. hydrocarbonoclasticus SP17 utilise les pili de type IV lors de la formation de biofilm sur les HOC. Ces appendices interviennent lors de l’adhésion de cette souche à des HOC ainsi que dans un processus de détachement d’un support hydrophobe. Les pili pourraient soit intervenir directement pour permettre à la bactérie de se détacher de la surface à laquelle elle s’est adhérée, soit indirectement par l’action de bactériophages. La présence d’une mobilité de type twitching sur les HOC a pu être également envisagée. Enfin, le rôle du système de sécrétion de type VI (T6SS), connu pour permettre à la bactérie d’interagir avec une cellule hôte, lors de la formation de biofilm mono-spécifique sur HOC, où aucun autre microorganisme que M. hydrocarbonoclasticus SP17 n’est présent, a été étudié. / Hydrophobic organic compounds (HOC), a large family of naturally-produced or anthropogenic molecules including lipids and hydrocarbons, represent a significant part of organic matter in marine ecosystems. Because of their low solubility in water, bacteria that degrade those compounds require the establishment of specific cell functions to increase their biodisponibility. Biofilm formation in water-HOC interface is one of these adaptations. The model of bacteria used in our laboratory, Marinobacter hydrocarbonoclasticus SP17, is able to form a biofilm on a wide range of HOC, such as alkanes, fatty alcohols and triglycerides, in order to use them as a carbon and energy source. The main purpose of my work was to broaden the knowledge of how bacteria adhere to and from biofilms on HOC, through the functional characterization of 10 candidate genes highlighted during proteomic and transcriptomic studies. Genetic tools and a gene-specific functional characterization have been developed in order to carry out this project. Functional study conducted on MARHY2686 revealed its involvement in the formation of biofilm on alkanes. Co-expression of MARHY2686 and the adjacent genes MARHY2687 and MARHY2685 durnig transcriptomic analysis together with their phylogenetic distribution and synteny conservation suggest that these three genes are involved in the same biological process. According to the high peptide sequence identity between MARHY2686 and AdeT, a periplasmic protein of a tripartite efflux pump system of Acinetobacter baumanii, MARHY2686 in combination with MARHY2687 and MARHY2685 could be the components of such a system. Other phenotypic observations would consider the involvement of MARHY2686 either in the assimilation of HOC or in the accumulation of intracellular lipid reserves. M. hydrocarbonoclasticus SP17 uses type IV pili during biofilm formation on HOC. These appendages are involved in the adhesion of this strain to and in a detachment process from HOC. Type IV pili could either act directly to allow bacteria to detach from the surface to which it is adhered, or indirectly through the action of bacteriophages. The presence of twitching motility on HOC has also been suggested. Finally, the role of the type VI secretion system (T6SS), a well-known protein system which allows interactions between bacteria and host cells, during the formation of a mono-species biofilm on HOC where no other microorganism than M. hydrocarbonoclasticus SP17 is present, has been studied.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / A Escherichia coli enteroagregativa (EAEC) é um patotipo emergente e heterogêneo que causa a diarréia aguda ou persistente em indivíduos de diferentes faixas etárias e em pacientes imunocomprometidos. Além disso, EAEC é um dos principais agentes etiológicos da diarréia dos viajantes. O padrão de aderência agregativa de EAEC está associado ao plasmídeo de aderência agregativa (pAA). Genes presentes no plasmídeo e no cromossomo codificam proteínas envolvidas na secreção extracelular de fatores de virulência na superfície ou diretamente na célula hospedeira. A capacidade de produção de muco e biofilme, elaboração de toxinas, aderência e indução de inflamação intensa na mucosa intestinal são importantes características da patogenicidade de EAEC. Nesse estudo, determinamos o perfil genotípico de genes do sistema de secreção Tipo V (SST5) e sistema de secreção Tipo VI (SST6) em cepas de EAEC. Os genes do SST5 ocorreram com mais frequência que os genes do SST6. A presença de pelo menos um gene do SST5 foi detectada em 79% das cepas, enquanto que os genes relacionados ao SST6 foram detectados em apenas 42% das cepas analisadas. A produção de biofilme foi observada em teste quantitativo e verificamos que 67% das cepas produziram biofilme. No teste qualitativo, o tipo de biofilme que predomina é o biofilme moderado (11 cepas), seguido do biofilme forte (9 cepas) e do biofilme discreto (4 cepas). A presença ou ausência de genes do SST5 e SST6 não parece interferir com a capacidade de produção de biofilme, nem com o tipo de biofilme formado. Em ensaios de citotoxicidade, apenas 25% das cepas EAEC (sobrenadante) causaram redução significativa na viabilidade de células T84 avaliada pelo teste de redução com MTT. Nossos resultados mostram que as cepas EAEC isoladas de crianças com diarréia aguda ou de grupo controle são invasoras para células T84. Ao compararmos a capacidade invasora das cepas clinicas e controle, observamos que a média do índice de internalização obtido nas 15 cepas do grupo clinico foi de 5,7% 1,7 e para as 9 cepas do grupo controle foi de 2.4 % 0,7; entretanto essa diferença observada não foi estatisticamente significativa. Não foi possível correlacionar o perfil genotípico dos genes do SST5 e SST6 com o perfil fenotípico analisado (formação de biofilme, citotoxicidade e invasão).O que pode ser atribuído a heterogeneidade genotípica e fenotípica, uma característica relevante de cepas EAEC. / Enteroaggregative Escherichia coli (EAEC) is an emerging and heterogeneous pathotype that causes acute or persistent diarrhea in individuals of different age groups and HIV-positive patients. In addition, EAEC is a major etiologic agent of travelers' diarrhea. The pattern of aggregative adherence of EAEC is associated with the aggregative adherence plasmid (pAA). Genes present in the plasmid and chromosome encode proteins involved in extracellular secretion of virulence factors on the surface or directly into the host cell. The production of mucus, biofilm and toxins; and induction of intense inflammation in the intestinal mucosa and mucosal adherence are major features of EAEC pathogenesis. In this study, we determined the genotypic profile of type V secretion system (T5SS) and type VI secretion system (T6SS) genes in EAEC strains. T5SS genes occurred more frequently than T6SS genes. The presence of at least one T5SS gene was detected in 79% of the strains, while genes related with T6SS were detected in only 42% of the strains tested. The biofilm production was observed in quantitative test, we have found that 67% of strains produced biofilm. In the qualitative test, we detected three distinctive patterns of biofilm formation: moderate (11 strains), strong (9 strains) and discrete biofilm (4 strains). The presence or absence of T5SS and T6SS genes do not interfere with the ability to produce biofilm, neither with biofilm pattern. In cytotoxicity assays, only 25% of EAEC strains (supernatant)resulted in significant reduction of T84 cells activity as evaluated by MTT reduction test. Our results show that EAEC strains isolated from children with acute diarrhea or the control group are able to invade T84 cells. When comparing the invasive ability of clinical and control strains, we observed that the average rate of internalization obtained in 15 clinical strains was 5.7% 1.7, for the nine strains of control group was 2.4% 0. 7, however this difference was not statistically significant. It was not possible to correlate the genotypic profile of T5SS and T6SS genes with the phenotypic profile analysed (biofilm formation, cytotoxicity and invasion), which can be attributed to genotypic and phenotypic heterogeneity, an important characteristic of EAEC strains

Conselho Nacional de Desenvolvimento Científico e Tecnológico / A Escherichia coli enteroagregativa (EAEC) é um patotipo emergente e heterogêneo que causa a diarréia aguda ou persistente em indivíduos de diferentes faixas etárias e em pacientes imunocomprometidos. Além disso, EAEC é um dos principais agentes etiológicos da diarréia dos viajantes. O padrão de aderência agregativa de EAEC está associado ao plasmídeo de aderência agregativa (pAA). Genes presentes no plasmídeo e no cromossomo codificam proteínas envolvidas na secreção extracelular de fatores de virulência na superfície ou diretamente na célula hospedeira. A capacidade de produção de muco e biofilme, elaboração de toxinas, aderência e indução de inflamação intensa na mucosa intestinal são importantes características da patogenicidade de EAEC. Nesse estudo, determinamos o perfil genotípico de genes do sistema de secreção Tipo V (SST5) e sistema de secreção Tipo VI (SST6) em cepas de EAEC. Os genes do SST5 ocorreram com mais frequência que os genes do SST6. A presença de pelo menos um gene do SST5 foi detectada em 79% das cepas, enquanto que os genes relacionados ao SST6 foram detectados em apenas 42% das cepas analisadas. A produção de biofilme foi observada em teste quantitativo e verificamos que 67% das cepas produziram biofilme. No teste qualitativo, o tipo de biofilme que predomina é o biofilme moderado (11 cepas), seguido do biofilme forte (9 cepas) e do biofilme discreto (4 cepas). A presença ou ausência de genes do SST5 e SST6 não parece interferir com a capacidade de produção de biofilme, nem com o tipo de biofilme formado. Em ensaios de citotoxicidade, apenas 25% das cepas EAEC (sobrenadante) causaram redução significativa na viabilidade de células T84 avaliada pelo teste de redução com MTT. Nossos resultados mostram que as cepas EAEC isoladas de crianças com diarréia aguda ou de grupo controle são invasoras para células T84. Ao compararmos a capacidade invasora das cepas clinicas e controle, observamos que a média do índice de internalização obtido nas 15 cepas do grupo clinico foi de 5,7% 1,7 e para as 9 cepas do grupo controle foi de 2.4 % 0,7; entretanto essa diferença observada não foi estatisticamente significativa. Não foi possível correlacionar o perfil genotípico dos genes do SST5 e SST6 com o perfil fenotípico analisado (formação de biofilme, citotoxicidade e invasão).O que pode ser atribuído a heterogeneidade genotípica e fenotípica, uma característica relevante de cepas EAEC. / Enteroaggregative Escherichia coli (EAEC) is an emerging and heterogeneous pathotype that causes acute or persistent diarrhea in individuals of different age groups and HIV-positive patients. In addition, EAEC is a major etiologic agent of travelers' diarrhea. The pattern of aggregative adherence of EAEC is associated with the aggregative adherence plasmid (pAA). Genes present in the plasmid and chromosome encode proteins involved in extracellular secretion of virulence factors on the surface or directly into the host cell. The production of mucus, biofilm and toxins; and induction of intense inflammation in the intestinal mucosa and mucosal adherence are major features of EAEC pathogenesis. In this study, we determined the genotypic profile of type V secretion system (T5SS) and type VI secretion system (T6SS) genes in EAEC strains. T5SS genes occurred more frequently than T6SS genes. The presence of at least one T5SS gene was detected in 79% of the strains, while genes related with T6SS were detected in only 42% of the strains tested. The biofilm production was observed in quantitative test, we have found that 67% of strains produced biofilm. In the qualitative test, we detected three distinctive patterns of biofilm formation: moderate (11 strains), strong (9 strains) and discrete biofilm (4 strains). The presence or absence of T5SS and T6SS genes do not interfere with the ability to produce biofilm, neither with biofilm pattern. In cytotoxicity assays, only 25% of EAEC strains (supernatant)resulted in significant reduction of T84 cells activity as evaluated by MTT reduction test. Our results show that EAEC strains isolated from children with acute diarrhea or the control group are able to invade T84 cells. When comparing the invasive ability of clinical and control strains, we observed that the average rate of internalization obtained in 15 clinical strains was 5.7% 1.7, for the nine strains of control group was 2.4% 0. 7, however this difference was not statistically significant. It was not possible to correlate the genotypic profile of T5SS and T6SS genes with the phenotypic profile analysed (biofilm formation, cytotoxicity and invasion), which can be attributed to genotypic and phenotypic heterogeneity, an important characteristic of EAEC strains