Previous research in our laboratory established that pyrB, pyrC or pyrD knock-out mutants in Pseudomonas aeruginosa required pyrimidines for growth. Each mutant was also discovered to be defective in the production of virulence factors. Moreover, the addition of exogenous uracil did not restore the mutant to wild type virulence levels. In an earlier study using non-pathogenic P. putida, mutants blocked in one of the first three enzymes of the pyrimidine pathway produced no pyoverdine pigment while mutants blocked in the fourth, fifth or sixth steps produced copious quantities of pigment, just like wild type P. putida. The present study explored the correlation between pyrimidine auxotrophy and pigment production in P. aeruginosa. Since the pigment pyoverdine is a siderophore it may also be considered a virulence factor. Other virulence factors tested included casein protease, elastase, hemolysin, swimming, swarming and twitching motilities, and iron binding capacity. In all cases, these virulence factors were significantly decreased in the pyrB, pyrC or pyrD mutants and even in the presence of uracil did not attain wild type levels. In order to complete this comprehensive study, pyrimidine mutants blocked in the fifth (pyrE) and sixth (pyrF) steps of the biosynthetic pathway were examined in P. aeruginosa. A third mutant, crc, was also studied because of its location within 80 base pairs of the pyrE gene on the P. aeruginosa chromosome and because of its importance for carbon source utilization. Production of the virulence factors listed above showed a significant decrease in the three mutant strains used in this study when compared with the wild type. This finding may be exploited for novel chemotherapy strategies for ameliorating P. aeruginosa infections in cystic fibrosis patients.

L’agent pathogène responsable de la tuberculose, Mycobacterium tuberculosis, utilise principalement les lipides comme source d’énergie lors du processus infectieux. Cela suggère que les enzymes lipolytiques (ELs) sont des facteurs d’une importance cruciale, qui jouent un rôle essentiel pour la survie et la persistance du bacille au sein des granulomes tuberculeux. Dans ce contexte, nous nous sommes intéressés au rôle physiologique de la protéine LipY (Rv3097c), une TAG-hydrolase apparentée à la lipase Hormono-sensible humaine. En utilisant un modèle expérimental de « foamy » macrophages, nous avons démontré que cette protéine sécrétée par le système de sécrétion ESX-5 était responsable de l’hydrolyse des triacylglycerols (TAG) de l’hôte dans la lumière phagosomale. Dans une seconde étude, nous avons développé un modèle expérimental robuste et réversible basé sur la biodisponibilité en azote et en carbone, deux facteurs essentiels qui gouvernent la formation et l’hydrolyse de TAG sous la forme d’inclusions lipidiques intracytoplasmiques (ILI) chez les mycobactéries. La simplicité d’utilisation de ce modèle s’avère être un excellent système biologique permettant d’étudier les propriétés phénotypiques des bacilles riches en ILI. L’ensemble des résultats obtenus au cours de ces travaux de thèse confirme que certaines ELs sont directement impliquées dans la virulence et/ou la survie des mycobactéries pathogènes. De plus, une très grande partie de ce travail ouvre de nouvelles perspectives sur la caractérisation et l’inhibition d’acteurs protéiques essentiels au métabolisme des lipides in vivo, offrant ainsi de nouvelles opportunités pour lutter contre M. tuberculosis. / Mycobacterium tuberculosis, the pathogenic agent responsible for tuberculosis (TB), mainly uses lipids as a source of energy during the infectious process. This suggests that lipolytic enzymes (LEs) are crucial metabolic agents that play a critical role in the survival and persistence of the bacillus within TB granulomas. In this context, we investigated the physiological role of the LipY protein (Rv3097c), a TAG-hydrolase related to the human Hormono-sensitive lipase. Using an experimental model of "foamy" macrophages, we demonstrated that this protein which is secreted by the ESX-5 secretion system, was responsible for the hydrolysis of host-derived triacylglycerols (TAGs) within the phagosomal compartment. In a second study, we developed a robust and reversible experimental model based on the bioavailability of nitrogen and carbon, two essential factors that govern the formation and hydrolysis of TAGs in the form of intracytoplasmic lipid inclusions (ILI) in mycobacteria. The simplicity of this model proves to be an excellent biological system for studying the phenotypic properties of ILI-rich bacilli. All the results obtained during this thesis confirm that some LEs are directly involved in the virulence and/or survival processes of pathogenic mycobacteria. In addition, we truly believe that this work opens up new perspectives on the characterization and inhibition of protein, that are essential actors for lipid metabolism in vivo, thus offering new opportunities to better control M. tuberculosis.

Orientador: Jesus Aparecido Ferro / Banca: Henrique Ferreira / Banca: Rafael Marini Ferreira / Banca: Fabricio José Jaciani / Banca; Helen Alves Penha / Resumo: Diante da importância do cancro cítrico para a citricultura mundial, a bactéria Xanthomonas citri subsp. citri, o agente causal da doença, tem sido amplamente estudada. Pesquisadores brasileiros realizaram o sequenciamento completo do genoma da X. citri subsp. citri isolado 306 (Xac306), com o intuito de elucidar os genes e mecanismos envolvidos na patogenicidade e/ou virulência da bactéria. As ORFs XAC2361 e XAC3898 possuem tamanhos e locais diferentes no genoma da Xac306, mas têm em comum o domínio Peptidase_M23, cujo processo biológico predito é de hidrolase de parede celular, mas a real função destas proteínas em Xac ainda é desconhecida. Este trabalho teve como objetivo avaliar, por meio da mutação sítio-dirigida, se as ORFs XAC2361 e XAC3898 estão relacionadas com a virulência e/ou patogenicidade de X. citri subsp. citri 306 e com o desenvolvimento do cancro cítrico. Para isso, foram realizados testes in vitro e in planta dos mutantes obtidos, visando observar alterações fenotípicas. Devido a presença de peptídeo sinal, a ORF XAC2361 foi fundida à proteína fluorescente mCherry (XAC2361-mCherry) para expressão in vivo e avaliação por microscopia de fluorescência. As análises fenotípicas demonstraram que o mutante ΔXAC2361 não apresentou alterações nos sintomas quando avaliado em limoeiro cravo (Citrus limonia Osbeck), porém apresentou menor capacidade de crescimento in vitro, menor motilidade swimming e swarming e menor capacidade de sobrevivência em SDS. Por outro lado,... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In view of the importance of citrus canker in citrus culture worlwide, the bacterium Xanthomonas citri subsp. citri, the causal agent of this disease, has been extensively studied. Brazilian researchers performed the complete sequencing of the genome of X. citri subsp. citri isolate 306 (Xac306), in order to elucidate the genes and mechanisms involved in the pathogenicity and/or virulence of Xac. The ORFs XAC2361 and XAC3898 have different sizes and location in the genome, but have in common the M23 Peptidase domain, whose biological process is predicted to act as cell wall hydrolase, but the actual function of these proteins in Xac is still unknown. This work aimed to evaluate, through site-directed mutagenesis, whether XAC2361 and XAC3898 ORFs are related to the virulence and / or pathogenicity of Xac306 and the development of citrus canker. In order to observe phenotypic changes, in vitro and in planta tests of the mutants were carried out. Due to the presence of signal peptide, the ORF XAC2361 was fused to the mCherry fluorescent protein (XAC2361-mCherry) for in vivo expression and fluorescence microscopy evaluation. Phenotypic analyzes demonstrated that the ΔXAC2361 mutant showed no change in symptoms when evaluated in Mexican lime (Citrus limonia Osbeck), but presented lower in vitro growth capacity, lower swimming and swarming motility, and lower survival capacity in SDS. On the other hand, the ΔXAC3898 mutant showed a significant reduction in virulence, lower in plant... (Complete abstract click electronic access below) / Doutor

Salmonella do grupo paratifóide é responsável por toxi-infecção alimentar no homem, veiculada por alimentos contaminados. Este estudo determinou o perfil genotípico de nove amostras de S. Typhimurium, a sua patogenicidade, assim como sua capacidade de colonização e invasão em aves SPF. Verificou-se pela análise dos genes: agfA, avrA, cdtB, fimA, fliC, invA, iroN, lpfC, mgtC, pefA, sefC, sifA, sipB, sipC, sitC, slyA, sopB, sopE1, sptP ou spvC em amostras de Salmonella Typhimurium que todas foram negativas para os genes sopE1 ou spvC. O gene cdtB estava presente em apenas uma amostra (11,11%) e o gene pefA em duas amostras (22,22%). O gene sefC foi encontrado em três amostras (33,33%). Em oito amostras (88,88%) os genes agfA, fimA, lpfC ou sptP estiveram presentes. Os genes avrA, fliC, invA, iroN, mgtC, sifA, sipB, sipC, sitC ou slyA ou sopB estiveram presentes em 100% das amostras analisadas. Determinou-se quatro perfis genotípicos. No ensaio de patogenicidade observou-se que as amostras inoculadas por via oral, não causaram mortalidade de pintinhos SPF de um dia de idade, com a exceção da amostra SA 633 e SA 006 que apresentaram 30 e 10%, respectivamente. No entanto, observou-se que a infecção por via subcutânea provocou uma maior mortalidade de pintinhos, sendo que as amostras SA 003, SA 004, SA 005 e a amostra vacinal mostraram somente 10% de mortalidade, a amostra SA 002 30%, as amostras SA 632 e SA 634 70% e a amostra SA 633 100%. A amostra SA 006 não provocou nenhuma mortalidade. A amostra mais patogênica pela via subcutânea foi a SA 633. O ensaio de colonização foi realizado em pintinhos SPF, com as amostras SA 002, SA 003, SA 004, SA 005, SA 006, SA 632, SA 633, SA 634 e amostra vacinal. Verificou-se ausência de invasão no fígado e baço 24 horas pós- infecção, exceto para as amostras SA 632 (30%) e amostra vacinal (20%). Após sete dias da infecção houve invasão em dois pintinhos com a amostra SA 002 e um pintinho com as amostras SA 004 e SA 005. Apenas na amostra SA 632 constatou-se colonização em ceco após 24 horas em 10% das amostras e após 7 dias em 70% pós-infecção. Concluiu-se que entre as amostras de Salmonella Typhimurium analisadas existiam diferentes perfis genotípicos baseando-se na presença ou ausência de genes de virulência, e que a amostra vacinal assemelha-se a amostras de S. Typhimurium estudadas quanto a presença dos genes. Os resultados do teste de patogenicidade das amostras de ST indicaram que a via de inoculação modifica a patogenicidade de uma mesma amostra e que a mortalidade após a inoculação pela via subcutânea é sempre superior que pela via oral. / Parathyphoid Salmonella are major food-borne pathogens spread by contaminated food products. This study determined the genotypic profile of nine samples of S. Typhimurium, pathogenicity, colonization and invasion in SPF chicks. It was found by analysis of genes: agfA, avrA, cdtB, fimA, fliC, invA, iroN, lpfC, mgtC, pefA, sefC, sifA, sipB, sipC, sitC, slyA, sopB, sopE1, sptP or spvC samples of S. Typhimurium all were negative to sopE1 or spvC. The cdtB gene was identified in one sample and pefA gene in two samples (22,22%). Sef C gene was detected in three samples (33,33%). In eight samples (88,88%) agfA, fimA, lpf or sptP were detected. AvrA, fliC, invA, iroN, mgtC, sifA, sipB, sipC, sitC, slyA and sopB were detected in all samples evaluated. Four genotypic profiles were established. Pathogenicity tests showed that samplesinoculated by oral gavage did not present mortality in one day old SPF chicks, except samples SA 633 and SA006 with 30 and 10%, respectively. However, it was observed that subcutaneous inoculation showed high mortality in SPF chicks than oral inoculation, and samples SA 003, SA004, SA005 and vaccinal strain showed 10% of mortality, 30% for sample SA002, 70% in the samples SA632 and SA 634 and 100% when the sample SA 633 was inoculated. No mortality was observed in sample SA006. Colonization test was performed in SPF chicks using the samples: SA002, SA 003, SA 004, SA005, SA006, SA 632, SA 633, SA 634 and vaccinal strain. The more pathogenic strain subcutaneously was the SA 633. There was not invasion in liver and spleen 24 hours p.i., except for sample SA 632 (30%) and vaccinal strain (20%). Seven days p.i. invasion was detected in two chicks inoculated with samples identified as SA 004 and SA 005. Sample SA 632 showed 10% of cecal colonization 24 hours p.i. and 70% after one week p.i. It was concluded that Salmonella Typhimurium strains including the vaccinal strain, showed different genotypical profiles, based on the presence or absence of genes of virulence genes. The results of the pathogenicity test indicated that inoculation route modify the pathogenicity of the same strain, and the mortality post-inoculation was always higher in chicks inoculated by subcutaneous route when compared to the oral route.

A proteína dispersina, codificada pelo gene aap, é um dos fatores de virulência de Escherichia coli enteroagregativa (EAEC). A detecção de aap tem sido utilizada juntamente com aggR e aatA no diagnóstico molecular de EAEC. Para verificar sua especificidade, esses genes foram pesquisados em 243 amostras de E. coli diarreiogênica (DEC). Todas as amostras foram negativas para os genes aggR e aatA, enquanto 26 amostras foram positivas para aap. Estas amostras haviam sido descritas como E. coli enteropatogênica atípica, entretanto essa classificação não foi confirmada, uma vez que elas não apresentaram o gene eae. Três amostras aderiram em células HEp-2 no padrão agregativo e foram classificadas como EAEC. O restante constituiu um grupo de amostras sem marcadores que caracterizam os patótipos de DEC. O seqüenciamento do gene aap de 6 amostras demonstrou alta homologia entre as seqüências obtidas e a seqüência da amostra protótipo de EAEC 042. Este estudo revelou que o gene aap não é exclusivo de EAEC. / The protein dispersin, encoded by aap, is one of the virulence factors of enteroaggregative Escherichia coli (EAEC). Detection of aap has been employed along with aggR and aatA in the molecular diagnosis of EAEC. In order to verify their specificity, these genes were searched in a collection of 243 diarrheagenic E. coli (DEC) strains. All of them were negative for aggR and aatA, whereas 26 were positive for aap. These strains have been described as atypical enteropathogenic E. coli. However, this classification was not confirmed since they did not harbor the eae gene. Three strains showed the aggregative adherence pattern to HEp-2 cells and were classified as EAEC. The remaining strains were part of a group that did not harbor any specific markers of DEC pathotypes. The DNA sequence analysis of 6 aap-harboring strains showed high homology between the sequence of these strains and the aap sequence of the EAEC prototype strain 042. This study revealed that aap is not exclusive of EAEC.

O objetivo deste estudo foi o de verificar a ocorrência de quatro genes de virulência em Salmonella Enteritidis de acordo com o fagotipo e ribotipo, assim como a virulência “in vivo". Os genes estudados foram invA, spvC, sefC e pefA em 120 amostras isoladas de várias fontes, pertencentes a diferentes fagotipos e ribotipos provenientes de sete estados brasileiros. Para a verificação da presença dos genes, as amostras foram examinadas pela técnica de Reação em Cadeia da Polimerase (PCR) individualmente e em multiplex. A ocorrência para o gene invA foi de 100% nas amostras (120/120), spvC em 94% (113/120), sefC em 97,5% (117/120) e pefA em 97% (116/120) das amostras. Foi possível caracterizar as amostras em cinco diferentes perfis. O primeiro, P1, foi positivo para os genes invA, spvC, sefC e pefA, P2 para invA, spvC e pefA, P3 para invA, sefC e pefA, P4 para invA e sefC e o último P5 para os genes invA e spvC. Para as amostras PT4RT1 obteve-se o perfil P1 em 94% (64/68), P2 em 1,5% (1/68), P3 em 3% (2/68) e P4 em 1,5% das amostras (1/68). Para as amostras PT4RT2, 86% (18/21) pertenceram ao perfil P1, 5% (1/21) ao P3 e 9% (2/21) das amostras ao perfil P4. Nas amostras PT4RT3 80% (4/5) pertenceram ao perfil P1 e 20% (1/5) ao P2. Nas amostras PT4TR9, 91% (10/11) pertenceram ao perfil P1 e 9% (1/11) ao P3. Todas as amostras PT4RT5, PT7RT1 e PT4RT10 pertenceram ao perfil P1 e apenas a amostra PT1 apresemtou o perfil P5. A virulência foi avaliada desafiando as aves via oral e subcutânea, através da colonização do ceco e invasão do fígado e baço. O gene spvC está relacionado com a sobrevivência e aumento da média de crescimento da bactéria no fígado e baço, mas neste estudo não demonstrou diferença na porcentagem de aves com reisolamento positivo para a bactéria nestes orgãos. Os genes sefC e pefA foram importantes para promover a colonização cecal, pois somente quando estes dois genes simultaneamente estiveram presentes no perfil, obteve-se o reisolamento cecal quando as aves foram desafiadas oralmente sendo esta via a principal rota de infecção deste patógeno. / This study has the intention of verify the four virulence genes event in Salmonella Enteritidis according with phage type and ribotype and the virulence “in vivo". The genes studied were invA, spvC, sefC and pefA in 120 Salmonella Enteritidis isolates from different origins, belongs at different ribotypes and phage types of seven Brazilian states. To verify the genes presence the strains were examined by Polimerase Chain Reaction (PCR) technique, singly and multiplex. The event of invA gene was in 100% (120/120) of strains, the spvC gene was in 94% (113/120) of strains, the sefC gene was in 97.5% (117/120) of strains and the pefA gene was in 97% (116/120) of strains. There were discovered five different profiles. The pattern one, P1, was positive for invA, spvC, sefC e pefA. The P2 was positive for invA, spvC and pefA. The P3 was positive for invA, sefC e pefA. The P4 was positive for invA and sefC and the last one, P5, was positive for invA and spvC. For the PT4RT1 strains, the P1 profile was present in 94% (64/68) of strains; P2 profile was in 1.5% (1/68); P3 in 3% (2/68); and P4 in 1.5% (1/68) of strains. For the PT4RT2 strains, the P1 profile was present in 86% (18/21) of strains; P3 profile was in 5% (1/21); and P4 in 9% (2/21) of strains. For the PT4RT3 strains, the P1 profile was present in 80% (4/5) of strains, and P2 in 20% (1/5) of strains. For the PT4RT9 strains, the P1 profile was present in 91% (10/11) of strains, and P3 in 9% (1/11) of strains. The strains: PT4RT5, PT7RT1 e PT4RT10 belongs at the P1 profile, and only the PT1 strain belongs at the P5’s profile. The virulence was evaluated challenging the birds orally and subcutaneous, through the colonization of the caecum, liver and spleen invasion. The gene spvC was related with the survivance and the increase of the average grow of the bacteria in the liver and spleen, but this study doesn’t demonstrate the difference in the percentage of positive birds for the bacteria in their organs. The sefC and pefA genes were important to promote the caecum colonization, because only when both genes were present simultaneously in the profile, obtain the caecum isolation when the birds were been by orally challenged this way the main route of the infection of this pathogen.

With the increase of antibiotic resistant bacteria strains, the need to determine the mechanisms of antimicrobial resistance is similarly rising. <i>Serratia marcescens</i>, a ubiquitous, Gram-negative opportunistic pathogen is known to have strong, natural resistance to diverse antimicrobial agents including antibiotics and antimicrobial peptides. Recently, we identified <i>S. marcescens</i> as one of the few bacteria resistant to antimicrobial compounds produced by <i>Stemphylium vesicarium</i>, an isolated fungal spinach endophyte. To identify the mechanism of antimicrobial resistance to the unknown <i>Stemphylium</i> antimicrobial compounds, we designed a transposon mutant screen identifying mutants sensitive to antimicrobial inhibition of bacterial growth. A transposon mutant library was constructed using the Tn5 EZ-Transposome (Epicentre) system and contains 1,824 individual mutants with 127 being identified as having a decreased resistance to the <i>Stemphylium</i> antimicrobial compounds. The transposon growth inhibition screen initially evaluates the mutants for reduced growth in the presence of 25% fungal metabolite over 24 hours. The growth phenotype is then confirmed in triplicate in a 12-hour time course growth experiment. Identification of the genomic insertion site of the Tn5 transposon utilized a multi-step modified nested-PCR protocol, termed TAIL-PCR. Following PCR purification, nanodrop spectroscopy and gel electrophoresis were performed to ensure the amplification purity of the extracted DNA and was subsequently sequenced via WideSeq analysis. BLAST identified insertions in genes necessary for membrane biogenesis, drug transport, pili formation, and iron metabolism. Future work is aimed at confirming these results and understanding the role of iron sequestration. Not only will this research contribute to our understanding of <i>S. marcescens</i> antimicrobial resistance mechanisms, but it aids in our understanding of the mechanisms of antimicrobial resistance development in other human pathogens.

As proteínas fosfatases desempenham um papel fundamental na modificação pós-traducional reversível de proteínas por fosforilação, ao atuarem na remoção do grupo fosforil estável de resíduos de serina, treonina e tirosina. Embora predominem em eucariotos, as serina/treonina fosfatases (STPs) também existem em bactérias, nas quais atuam controlando diversos aspectos fisiológicos e de virulência. Neste trabalho investigamos o papel das STPs na virulência e fisiologia de Chromobacterium violaceum, uma ?-proteobactéria que atua como um patógeno ocasional de humanos e é amplamente encontrada em água e solos de regiões tropicais e subtropicais. Análises in silico revelaram a presença de quatro STPs no genoma de C. violaceum, sendo que duas possuem apenas o domínio de fosfatase (CV_0881 e CV_3848) e duas possuem um domínio adicional de regulador de resposta (CV_2644 e CV_3505). Mutantes nulos foram construídos para as quatro STPs e todas estas linhagens apresentaram crescimento semelhante ao da linhagem selvagem em meio rico e meio mínimo. As linhagens mutantes ?0881, ?2644 e ?3505 não apresentaram alteração de virulência em camundongos. Os mutantes ?2644 e ?3505 apresentaram menor formação de biofilme, o que sugere papel dessas fosfatases neste processo. Uma caracterização mais aprofundada da linhagem ?3848 por diferentes técnicas de microscopia revelou que este mutante apresenta células de tamanho diminuído, irregularidades no envelope celular e problemas na distribuição do DNA. Estes dados sugerem que CV_3848 tem papel em divisão celular, condensação do material genético e manutenção da parede celular. Nos ensaios de virulência o mutante ?3848 mostrou menor capacidade de causar morte e manter-se no fígado de camundongos, indicando que a STP CV_3848 é importante na patogenicidade de C. violaceum. / Protein phosphatases play a key role in reversible post-translational modification of proteins through phosphorylation since they act removing the stable phosphoryl group of serine, threonine and tyrosine residues. Although dominant in eukaryotes, the serine/threonine phosphatases (STPs) also exist in bacteria, in which they act by controlling various physiological and virulence traits. In this work we investigated the role of STPs on the virulence and physiology of Chromobacterium violaceum, a ?-proteobacterium that occasionally acts as a pathogen of humans and it is widely found in water and soil of tropical and subtropical regions. In silico analyzes revealed the presence of four STPs in the genome of C. violaceum, two of which have only the phosphatase domain (CV_0881 and CV_3848) and two that possess an additional domain of response regulator (CV_2644 and CV_3505). Null mutants were constructed for the four STPs and all of them showed similar growth to the wild type strain on rich and minimal medium. The mutant strains ?0881, ?2644 and ?3505 did not show any change in virulence in mice. The ?2644 and ?3505 mutants had lower biofilm formation, suggesting the role of these phosphatases in this process. Further characterization of ?3848 by different microscopy techniques revealed that this mutant presents cells of diminished size, irregularities in the cellular envelope and problem on the DNA distribution. These data suggest that CV_3848 has role in cell division, condensation of the genetic material and cell wall maintenance. In virulence assays the ?3848 mutant showed a lower ability to cause death and to remain in the liver of mice, indicating that the STP CV_3848 is important for the pathogenicity of C. violaceum.

Staphylococcus aureus and methicillin resistant Staphylococcus aureus (MRSA) are important pathogens of humans and livestock, including dairy cows. In livestock it represents a concern for public health as it may act as a reservoir that can infect humans and provide a source of transferrable resistance genes. The divergent mecA gene, mecC, was first identified in dairy cows in the UK, and has since been detected in many species in continental Europe. However, limited data exists on the epidemiological characteristics or the transmission dynamics of bovine mecC MRSA in the UK. S. aureus Mobile Genetic Elements (MGEs) often encode virulence and antimicrobial resistance genes that can contribute to the pathogenicity of the strain. Acquisition or loss of MGEs and variations within the core genome are reported to play an important role in S. aureus host adaptation although the mechanisms underlying S. aureus host specificity are not fully understood. This study was undertaken to determine the antimicrobial resistance and bovine associated virulence features of S. aureus isolated from bovine milk. The first two chapters of this thesis comprise of an introduction and a description of the methods used. Chapter 3 describes bovine associated features in bulk tank milk S. aureus isolates. SaPI borne-vwb and sec_bovine were widespread. Further, genome analysis detected six new SaPIs harbouring these genes and a class of site-specific integrases that appear to be associated with ruminant derived isolates. Examination of the fnbpA gene identified host specific variations that may be used to distinguish bovine from human isolates. Chapter 4 presents data on the epidemiological characteristics of mecC MRSA at the cow level within a dairy herd. Data from a longitudinal study undertaken suggested that mecC MRSA infections were transient and may not be associated with clinical disease. The prevalence varied between 1.14%-5.07% during the one-year study period, while SNP based whole genome phylogeny revealed four possible chains of transmission. Chapter 5 details a survey conducted to detect the prevalence of MRSA in UK retail meat. No mecC MRSA were found however CC398 were found and compared to CC398 isolates from the bulk tank milk study. A phylogenetic study provided no evidence of a common lineage of livestock association MRSA colonising both cattle and pigs in the UK. Chapter 6 describes the characterisation of a novel Streptococcus species isolated from a mastitic cow from New Zealand. Genome sequencing and phenotypic studies revealed this isolate, originally thought to be Streptococcus uberis to be most closely related to Streptococcus pseudoporcinus.

A proteína dispersina, codificada pelo gene aap, é um dos fatores de virulência de Escherichia coli enteroagregativa (EAEC). A detecção de aap tem sido utilizada juntamente com aggR e aatA no diagnóstico molecular de EAEC. Para verificar sua especificidade, esses genes foram pesquisados em 243 amostras de E. coli diarreiogênica (DEC). Todas as amostras foram negativas para os genes aggR e aatA, enquanto 26 amostras foram positivas para aap. Estas amostras haviam sido descritas como E. coli enteropatogênica atípica, entretanto essa classificação não foi confirmada, uma vez que elas não apresentaram o gene eae. Três amostras aderiram em células HEp-2 no padrão agregativo e foram classificadas como EAEC. O restante constituiu um grupo de amostras sem marcadores que caracterizam os patótipos de DEC. O seqüenciamento do gene aap de 6 amostras demonstrou alta homologia entre as seqüências obtidas e a seqüência da amostra protótipo de EAEC 042. Este estudo revelou que o gene aap não é exclusivo de EAEC. / The protein dispersin, encoded by aap, is one of the virulence factors of enteroaggregative Escherichia coli (EAEC). Detection of aap has been employed along with aggR and aatA in the molecular diagnosis of EAEC. In order to verify their specificity, these genes were searched in a collection of 243 diarrheagenic E. coli (DEC) strains. All of them were negative for aggR and aatA, whereas 26 were positive for aap. These strains have been described as atypical enteropathogenic E. coli. However, this classification was not confirmed since they did not harbor the eae gene. Three strains showed the aggregative adherence pattern to HEp-2 cells and were classified as EAEC. The remaining strains were part of a group that did not harbor any specific markers of DEC pathotypes. The DNA sequence analysis of 6 aap-harboring strains showed high homology between the sequence of these strains and the aap sequence of the EAEC prototype strain 042. This study revealed that aap is not exclusive of EAEC.