Este estudo identificou a presença e a viabilidade de Streptococcus spp., Propionibacterium acnes e Enterococcus faecalis antes e após os procedimentos endodônticos, utilizando o método de reação de cadeia de polimerase (PCR) baseado em RNA ribossômico (rRNA) e seus respectivos genes (rDNA). Foram coletadas amostras de 20 dentes com infecção primária antes (S1) e após o preparo químico-cirúrgico (S2), e depois do emprego do Ca(OH)2 como medicação intracanal (S3). DNA e RNA foram extraídos da mesma amostra de canal radicular e utilizados como moldes para reação de PCR com iniciadores específicos para a região 16S rRNA das espécies analisadas. Streptococcus espécies foram detectados em 20% e 25% das amostras S1 utilizando os métodos baseados em rRNA e rDNA, respectivamente; enquanto P. acnes foi detectado apenas pela análise de rRNA, estando presente em 10% das amostras S1. Após o preparo químico-cirúrgico, Streptococcus spp. foram detectado em 10% das amostras S2 quando se utilizou rDNA, porém não foi detectado pelo método baseado em rRNA, indicando ausência de células viáveis. Por outro lado, P. acnes foi detectado por ambos os métodos nas amostras S2, com prevalência de 10% e 5% quando se utilizou rRNA e rDNA como molde para PCR, respectivamente. Nas amostras S3, P. acnes foi a única espécie detectada nos ensaios baseados em rRNA, presente em 10% dos casos, enquanto o método baseado em rDNA falhou em detectar essa espécie. Por sua vez, E. faecalis não foi detectado em nenhuma amostra pelos métodos utilizados. Portanto, concluise que a suscetibilidade bacteriana aos procedimentos endodônticos varia entre as espécies Gram-positivas. Enquanto Streptococcus spp. foram suscetíveis, P. acnes persistiu ativo em canais radiculares após o preparo químico-cirúrgico e medicação intracanal. Esses dados sugerem que há necessidade de novas estratégias para a eliminação de espécies resisitentes ao tratamento endodôntico. / This study identified the presence and viability of Streptococcus spp., Enterococcus faecalis and Propionibacterium acnes before and after endodontic procedures, using the polymerase chain reaction (PCR) based on ribosomal RNA (rRNA) and their genes (rDNA ). Samples of 20 teeth with primary infection were collected before (S1) and after chemical-surgical preparation (S2), and after Ca(OH)2 as temporary dressing (S3). DNA and RNA were extracted from the same root canal sample and used as templates for PCR with specific primers for 16S rRNA region of the analyzed species. Streptococcus species were detected in 20% and 25% of the S1 samples using methods based on rRNA and rDNA, respectively; while P. acnes was only detected by analysis of rRNA, present in 10% of the samples S1. After chemicalsurgical preparation, Streptococcus spp. were detected in 10% of S2 samples when using rDNA as template, but they were not detected by the method based on rRNA, indicating the absence of viable cells. Furthermore, P. acnes was detected by both methods in samples S2, with a prevalence of 10% and 5% when using as template rRNA and rDNA for PCR, respectively. In S3 samples, P. acnes was the only species detected in assays based on rRNA, present in 10% of cases, while the rDNA-based method failed to detect this species. E. faecalis was not detected in any sample by the methods used. Therefore, it is concluded that bacterial susceptibility to endodontic procedures may vary among Gram-positive species. While Streptococcus spp. were susceptible, P. acnes persisted active in root canals after chemicalsurgical preparation and dressing. These data suggest the need for new strategies to eliminate resisitant species to endodontic treatment.

Streptococcus equi is the causative agent of strangles, a prevalent and highly contagious disease of horses. Despite the animal suffering and economic burden associated with strangles, little is known about the molecular basis of S. equi virulence. Here we have investigated the contributions of a specific lipoprotein and the general lipoprotein processing pathway to the abilities of S. equi to colonize equine epithelial tissues in vitro and to cause disease in both a mouse model and the natural host in vivo. Colonization of air interface organ cultures after they were inoculated with a mutant strain deficient in the maturase lipoprotein (prtM138-213, with a deletion of nucleotides 138 to 213) was significantly less than that for cultures infected with wild-type S. equi strain 4047 or a mutant strain that was unable to lipidate preprolipoproteins (lgt190-685). Moreover, mucus production was significantly greater in both wild-type-infected and lgt190-685-infected organ cultures. Both mutants were significantly attenuated compared with the wild-type strain in a mouse model of strangles, although 2 of 30 mice infected with the lgt190-685 mutant did still exhibit signs of disease. In contrast, only the prtM138-213 mutant was significantly attenuated in a pony infection study, with 0 of 5 infected ponies exhibiting pathological signs of strangles compared with 4 of 4 infected with the wild-type and 3 of 5 infected with the lgt190-685 mutant. We believe that this is the first study to evaluate the contribution of lipoproteins to the virulence of a gram-positive pathogen in its natural host. These data suggest that the PrtM lipoprotein is a potential vaccine candidate, and further investigation of its activity and its substrate(s) are warranted.

Gram-positive bacteria are part of the normal flora of fish from different aquatic environments. They are mesophilic bacteria and demonstrate optimum growth at ambient temperature. In the sub-tropics, marine fish are caught from seas at temperatures of 16 to 34C, they are usually not iced and are handled at ambient temperature. It was hypothesized that under these conditions Gram-positive bacteria will be abundant in sub-tropical marine fish and will have roles in the spoilage of fish. A review of literature showed that there is a gap in understanding the Gram-positive bacterial populations in sub-tropical marine fish. This is partly due to the fact that the selective media used for isolating Gram-positive bacteria have limitations. Ecological and speciation studies have revealed that the ecology and speciation of many Gram-positive bacteria have not been clearly elucidated. The effect of ambient storage on the individual genera and species of Gram-positive bacteria in fish has been rarely studied. The spoilage potential of Gram-positive bacteria of marine fish origin has not been clearly determined. Therefore, the main aims of this study were to isolate Gram-positive bacteria from fresh and ambient-temperature-stored sub-tropical marine fish, speciate the isolates and study the spoilage potential of the isolates. The practical components of this study were conducted in four parts. The first part dealt with validation of tryptone soya agar with 0.25% phenylethyl alcohol (PEA-TSA) to enumerate Gram-positive bacteria. The second part enumerated Gram-positive bacteria from the muscles, gills and gut of Pseudocaranx dentex (Silver Trevally), Pagrus auratus (Snapper) and Mugil cephalus (Sea Mullet) stored at 25C for 15 hours using PEA-TSA. The third part dealt with the speciation of the isolates using appropriate methods such as polymerase chain reaction, 16S rRNA gene sequence, the VITEK JR system and conventional biochemical methods. In the fourth part, the isolates were assayed qualitatively for their ability to produce volatile sulphur compounds (VSC), reduce trimethylamine oxide and decarboxylate histidine, lysine and ornithine at mesophilic temperature, 32C. Initial studies indicated that PEA-TSA significantly (P< 0.05) reduced the total aerobic bacterial count of fish whereas control Gram-positive bacteria were not affected (P> 0.05). Gram-positive aerobic bacterial counts (GABC) significantly (P< 0.05) increased in the muscles and gills during ambient storage for 15 hours. Within each species, no significant (P> 0.05) differences were found in GABC between muscles and gills. Moreover, there were no significant differences (P> 0.05) in GABC between fish species during storage. In total, 390 bacteria were isolated from the fresh and stored fish; 339 isolates (87%) were found to be Gram-positive. Two hundred and sixty-six isolates (78%) of Gram-positive bacteria were identified to fall into 13 genera, namely Staphylococcus, Micrococcus, Bacillus, Virgibacillus, Brevibacillus, Corynebacterium, Streptococcus, Enterococcus, Aerococcus, Exiguobacterium, Carnobacterium, Vagococcus and Sporosarcina and 30 species. In fresh fish, Staphylococcus epidermidis and Micrococcus luteus were the most frequent isolates. The effect of storage at 25C for 15 hours resulted in a change of Gram-positive bacterial populations; while S. epidermidis, S. xylosus and Bacillus megaterium were no longer present, S. warneri, B. sphaericus, Brevibacillus borstelensis, Enterococcus faecium and Streptococcus uberis increased. Three species, E. faecium, Str. uberis and B. sphaericus, were the most prevalent at the end of storage. Micrococcus luteus and S. warneri were the most prevalent isolates from Pseudocaranx dentex, but E. faecium and Str. uberis were the most frequently isolated from Pagrus auratus and Mugil cephalus. With respect to different parts of the fish body, E. faecium, Str. uberis and B. sphaericus were the most frequent isolates from the muscles, E. faecium, Str. uberis from the gills and M. luteus from the gut. Among the 228 isolates examined, Br. borstelensis 73, Br. borstelensis 291, Str. uberis 339, Vagococcus fluvialis 31 and Vag. fluvialis 132 produced VSC from sodium thiosulphate, cysteine and methionine. However, strains varied in sulphur source utilization. Exiguobacterium acetylicum 5, Exiguobacterium spp. 191, Carnobacterium spp. 338, Br. borstelensis 73, Br. borstelensis 291, Str. uberis 30, Str. uberis 339, Vag. fluvialis 31 and Vag. fluvialis 132 reduced TMAO. No histidine decarboxylase activity was found in the Gram-positive bacterial species tested. Lysine and ornithine were decarboxylated mainly by different strains of S. warneri, S. epidermidis and M. luteus. During ambient storage of fish, the frequency of lysine-decarboxylating bacteria increased and became more diverse after 5 hours of storage. Among fish species examined, the frequencies of lysine- and ornithine-decarboxylating bacteria were higher and more diverse in Pseudocaranx dentex than in Pagrus auratus and Mugil cephalus. This study found that Gram-positive bacteria were abundant and diverse in sub-tropical marine fish; however, their frequencies were affected by fish habitat and fish body part. Ambient temperature storage determined which Gram-positive bacterial species were dominant. With the exception of one isolate of S. aureus, Gram-positive bacteria isolated from sub-tropical marine fish caught from unpolluted water were not potential pathogens. The study also showed that Gram-positive bacteria had greater ability to decarboxylate lysine and ornithine than to produce VSC or reduce TMAO, and the spoilage potential of a bacterial species was a strain-dependent behaviour. This is a significant study as it is the first study on this aspect sub-tropical marine fish. It validated a selective medium that can be used to enumerate most Gram-positive bacteria from a marine environment. Most of the Gram-positive bacterial species from sub-tropical marine fish identified in this study were documented for the first time. The effects of ambient storage and the spoilage potential of Gram-positive bacteria from sub-tropical marine were clearly elucidated.

Les maladies infectieuses dues aux bactéries Gram + sont causes de mortalité importante à travers le monde, et de récentes études ont mis en évidence le rôle pathologique de l’interféron de type I (I IFN) dans ces maladies. Les cellules dendritiques plasmacytoïdes (pDC) produisent des quantités importantes d’IFN de type I suite à la détection de virus. Des données récentes suggèrent que les pDC humaines pourraient également détecter des bactéries, mais les récepteurs impliqués restent inconnus. Au cours de ma thèse, j’ai caractérisé l’expression des récepteurs TLR2 / 1 par les pDC. Ces deux récepteurs permettent aux pDC de détecter les lipoprotéines bactériennes. Je montre que les pDC répondent aux bactéries Gram + (M. tuberculosis, S. aureus et L. monocytogenes) par la voie TLR2 / 1. Mon travail a montré que les pDC primaires humaines expriment TLR1 et TLR2 à la fois au niveau de l'ARNm et au niveau protéique. En réponse aux lipoprotéines bactériennes, la régulation des molécules costimulatrices par les pDCs est TLR1-dépendante tandis que la sécrétion d’I-IFN est TLR2-dépendante. De plus, TLR2 et TLR1 jouent des rôles distincts au cours du priming des cellules T CD4+ naïves par les pDCs, induisant une prolifération et différentiation en sous-populations Th1 / Th2 / Treg. Je démontre en outre que ces différences reposent sur les voies de signalisation distinctes de ces deux TLR. Ce travail de thèse pose ainsi les bases pour l’exploration du rôle des pDC dans les infections bactériennes humaines. / Infections by Gram+ bacteria are worldwide life-threatening diseases where new studies are highlighting the pathological role of Type I interferon (I IFN). Plasmacytoid dendritic cells (pDCs) are the main source of Type I IFN following viral sensing. Recent evidence suggests that human pDCs might sense bacteria. The receptors mediating bacterial sensing in pDCs are not known. During my thesis, I focused on the characterization of pDCs TLR2/1 receptors expression. These two receptors allow pDCs to sense Gram+ bacterial lipoproteins. My work showed that human primary pDCs express TLR1 and TLR2 at the mRNA and protein level. I show that pDCs respond to the Gram+ bacteria M. tuberculosis, S. aureus and L. monocytogenes through TLR2/1 pathway. In human primary pDC, I found that in response to bacterial lipoproteins up-regulation of costimulatory molecules is TLR1-dependent while IFN-I secretion is TLR2-dependent. TLR2 and TLR1 signalling play a different role in the pDCs priming of naïve CD4+ T-cells, inducing proliferation and differentiation to TH1/TH2/Treg subsets. I further demonstrate that these differences rely on the diverse signaling pathway activated by the two TLRs. This work provides the rationale to explore pDCs activity in human bacterial infection.

No / Mono- and disaccharide-functionalised conjugates of the fluoroquinolone antibiotic ciprofloxacin have been synthesised and used as chemical probes of the bacterial uptake of glycosylated ciprofloxacin. Their antimicrobial activities against a panel of clinically relevant bacteria were determined: the ability of these conjugates to inhibit their target DNA gyrase and to be transported into the bacteria was assessed by using in vivo and in vitro assays. The data suggest a lack of active uptake through sugar transporters and that although the addition of monosaccharides is compatible with the inhibition of DNA gyrase, the addition of a disaccharide results in a significant decrease in antimicrobial activity.

Orientador: Elisa Helena Giglio Ponsano / Resumo: O objetivo deste estudo foi investigar a composição química e as atividades antimicrobiana e antioxidante dos extratos etanólicos de Curcuma longa e Bixa orellana, na busca por substituintes aos aditivos sintéticos utilizados na indústria de alimentos. Pela espectrometria de massa (GC-MS) foram identificados bisdemetoxicurcumina, demetoxicurcumina e curcumina no extrato de C. longa e prunina e naringenina no extrato de B. orellana. C. longa apresentou atividade antimicrobiana frente a Clostridium sporogenes e Staphylococcus aureus, com concentração bactericida mínima (CBM) de 25 mg/mL e 156 µg/mL, respectivamente. O extrato de B. orellana apresentou CBM de 50 mg/mL para C. sporogenes e 625 µg/mL para S. aureus. Nenhum dos extratos apresentou atividade bactericida para Escherichia coli e Salmonella Typhimurium. A atividade antioxidante dos extratos foi evidenciada pelos métodos Poder Antioxidante por Redução Férrica (FRAP) e Capacidade de Absorção do Radical Oxigênio (ORAC). O extrato de B. orellana apresentou maior atividade antioxidante pelos métodos FRAP e ORAC (277,70 e 455,17 mM trolox equivalente/g, respectivamente) do que o extrato de C. longa (129,74 e 217,98 mM trolox equivalente/g, respectivamente). Os efeitos biológicos dos extratos etanólicos de C. longa e B. orellana revelados no presente estudo apontaram seu potencial para a utilização na indústria de alimentos como uma alternativa aos aditivos sintéticos. / Abstract: The objective of this study was to investigate the chemical composition and the antimicrobial and antioxidant activities of Curcuma longa and Bixa orellana ethanolic extracts, in the search for alternatives to the synthetic additives used in the food industry. Mass spectrometry (GC-MS), identified bisdemethoxycurcumin, demethoxycurcumin and curcumin in the extract of C. longa and prunin and naringenin in the extract of B. orellana. C. long showed antimicrobial activity against Clostridium sporogenes and Staphylococcus aureus, with a minimum bactericidal concentration (MBC) of 25 mg/mL and 156 μg/mL, respectively. MBC of B. orellana extract was 50 mg/mL for C. sporogenes and 625 μg/mL for S. aureus. None of the extracts showed bactericidal activity against Escherichia coli and Salmonella Typhimurium. The antioxidant activity of the extracts was evidenced by the methods Iron Reduction Antioxidant Power (FRAP) and Oxygen Radical Absorption Capacity (ORAC). B. orellana extract had higher antioxidant activity by FRAP and ORAC (277.70 and 455.17 mM trolox equivalent/g, respectively) than C. longa extract (129.74 and 217.98 mM trolox equivalent/g, respectively). The biological effects of C. longa and B. orellana ethanolic extracts revealed in this study indicated their potential as an alternative to synthetic additives used in the food industry. / Mestre

Diss. Linköping : Linköpings universitet, 2007.

Thesis (MScFoodSc)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: The regular consumption of probiotics is becoming a recognized trend in the food industry due to several reported health benefits. A probiotic is defined as a live microbial feed supplement that beneficially affects the host animal by improving its intestinal microbial balance. A wide variety of probiotic food products are available on the South African market and comprise an assortment of fermented milks, as well as lyophilized preparations in tablet or capsule form. Strains of Lactobacillus acidophilus and Bifidobacterium species are mostly used as probiotic microbes in the industry due to their health enhancing effect. The survival of sensitive probiotic microbial species in food matrices are influenced by various factors such as oxygen concentration, pH levels and manufacturing and storage conditions. These should be considered and monitored as the South African food and health regulations stipulate that probiotic microbes should be present at a concentration of 10⁶ cfu.ml ̄ ¹' in order to exert a beneficial effect. Some health benefits are also correlated to specific microbial species and strains and these factors have resulted in the need for the rapid and accurate identification of probiotic microbes present in food products. The probiotic microbes present in probiotic yoghurts and supplements have in the past been identified using traditional methods such as growth on selective media, morphological, physiological and biochemical characteristics. However, even some of the most sophisticated cultural-dependant techniques are not always sufficient for the identification and classification of especially Bifidobacterium, as well as closely related Lactobacillus species. Molecular techniques are more often employed for the rapid and accurate detection, identification and characterization of microbial species present in food products. The aim of this study was to detect and identify the probiotic species present in various commercial South African yoghurts and lyophilized preparations using peR-based DGGE analysis. A 200 bp fragment of the V2-V3 region of the 16S rRNA gene was amplified and the peR fragments were resolved by DGGE. The unique fingerprints obtained for each product were compared to two reference markers A and B in order to identify the bands present. The results obtained were verified by species-specific peR, as well as sequence analyses of bands that could not be identified when compared to the reference markers. Only 54.5% of the South African probiotic yoghurts that were tested did contain all the microbial species as were mentioned on the labels of these products, compared to merely one third (33.3%) of the lyophilized probiotic food supplements. Some Bifidobacterium species were incorrectly identified according to some product labels, while other products contained various microbes that were not mentioned on the label. Sequence analysis confirmed the presence of a potential pathogenic Streptococcus species in one of the yoghurt products and in some instances the probiotic species claimed on the labels were non-scientific and misleading. The data obtained in this study showed that the various South African probiotic products tested were of poor quality and did not conform to the South African regulations. peR-based DGGE analysis proofed to be a valuable approach for the rapid and accurate detection and identification of the microbial species present in South African probiotic products. This could help with future implementation of quality control procedures in order to ensure a reliable and safe probiotic product to the consumer. / AFRIKAANSE OPSOMMING: Die gereelde inname van probiotiese produkte is besig om In erkende tendens in die voedselindustrie te word, as gevolg van verskeie gesondheidsvoordele wat daaraan gekoppel word. In Probiotika word gedefinieer as In voedingsaanvulling wat uit lewendige mikrobes bestaan en wat In voordelige effek op mens of dier het deur In optimale mikrobiese balans in die ingewande te handhaaf. In Wye verskeidenheid probiotiese voedselprodukte is tans beskikbaar op die Suid- Afrikaanse mark. Hierdie bestaan hoofsaaklik uit verskeie gefermenteerde melkprodukte asook 'n reeks tablette en kapsules wat probiotiese mikrobes in gevriesdroogde vorm bevat. Lactobacillus acidophilus tipes en Bifidobacterium spesies word die algemeenste in die voedselindustrie gebruik aangesien hierdie spesifieke mikrobes bekend is om goeie gesondheid te bevorder. Die oorlewing van sensitiewe probiotiese mikrobiese spesies in voedsel matrikse word beïnvloed deur faktore soos suurstof konsentrasie, pH-vlakke en vervaardigings- en opbergings kondisies. Hierdie faktore moet in aanmerking geneem word en verkieslik gemonitor word aangesien die Suid-Afrikaanse voedsel en gesondheids regulasies stipuleer dat probiotiese mikrobes teen In konsentrasie van 10⁶ kolonie vormende eenhede per ml teenwoordig moet wees om In voordelige effek te toon. Sommige gesondheidsvoordele word direk gekoppel aan spesifieke mikrobiese spesies en spesie-tipes. Hierdie faktore het gelei tot In groot aanvraag na vinnige en akkurate metodes vir die identifikasie van probioties mikrobes in voedselprodukte. Die probiotiese mikrobes teenwoordig in probiotiese joghurts en ook die gevriesdroogde vorms in tablette en kapsules, was al geïdentifiseer deur gebruik te maak van tradisionele metodes soos groei op selektiewe media, morfologiese, fisiologiese en biochemiese eienskappe. Selfs van die mees gesofistikeerde kultuur-afhanklike tegnieke is egter nie altyd voldoende vir die identifikasie en klassifikasie van veral Bifidobacterium en na-verwante Lactobacillus spesies nie. Molekulêre metodes word dikwels aangewend vir die vinnige en akkurate deteksie, identifikasie en karakterisering van mikrobes teenwoordig in voedselprodukte. Die doel van hierdie studie was om die probiotiese mikrobes teenwoordig in verskeie Suid-Afrikaanse joghurts en gevriesdroogde aanvullings, te identifiseer deur gebruik te maak van polimerase kettingreaksie (PKR)-gebaseerde denaturerende gradiënt jelelektroforese (DGGE) analise. 'n PKR fragment van 200 bp van die V2-V3 gedeelte van die 16S ribosomale RNS (rRNS) geen is geamplifiseer, en die PKR fragmente is geskei met behulp van DGGE. Die unieke vingerafdrukke wat verkry is vir elke produk is teen twee verwysings merkers A en B vegelyk om die bande teenwoordig in die profiele te identifiseer. Die resultate is bevestig deur spesies-spesifieke PKR en ook deur die ketting volgordes van die DNS fragmente te bepaal wat nie geïdentifiseer kon word deur vergelyking met die verwysings merkers nie. Slegs 54.5% van die Suid-Afrikaanse probiotiese joghurts wat getoets is het al die mikrobiese spesies bevat soos aangedui was op die etikette van hierdie produkte, teenoor slegs 'n derde (33.3%) van die gevriesdroogde voedingsaanvullings. Sekere Bifidobacterium spesies is verkeerd geïdentifiseer op sommige van die produk etikette, terwyl ander produkte verskeie mikrobes bevat het wat nie op die etiket aangedui was nie. 'n Potensiële patogeniese Streptococcus spesie is in een van die joghurt produkte gevind soos bevestig deur DNS kettingvolgorde bepalings. In sommige gevalle was die probiotiese spesienaam wat aangedui is op die etiket onwetenskaplik en misleidend. Die resultate wat uit hierdie studie verkry is dui aan dat die Suid-Afrikaanse probiotiese produkte wat getoets is van 'n swak gehalte is en nie aan die Suid- Afrikaanse regulasies voldoen nie. Daar is getoon dat PKR-gebaseerde DGGE analise 'n waardevolle tegniek kan wees vir die akkurate deteksie en identifisering van die mikrobiese spesies teenwoordig in probiotiese produkte. Dit kan help met die toekomstige implementering van kwaliteitskontrolerings prosedures om 'n mikrobiologiese betroubare en veilige produk aan die verbruiker te verseker.

Rhodococcus fascians is a Gram-positive phytopathogenic bacterium which induces the development of leafy galls, local amplifications of multiple buds, on most infected plants. This process is linked to the production of phytohormones along with the presence of essential virulence-associated genes like the plasmid loci att and fas and the chromosomal gene vicA. However, the presence of these genes is not sufficient to ensure the infection phenotype development, indicating that other genes play a role in R. fascians pathogenicity. In this work, we studied the metabolic modifications occurring when the bacterium interacts with its host using a proteomic approach. A comparison between virulent and avirulent strains showed variations in the expression of catalases. In the virulent strain, besides the transitory induction of the att locus expression, the bacterium changes its metabolism from the Krebs cycle to the glyoxylate shunt, a process which is frequently observed in bacteria confronted to a hostile environment. The expression of the shunt-specific enzyme isocitrate lyase increased, while expression of fumarate hydratase and pyruvate dehydrogenase decreased. Hence, we focused on the link between the glyoxylate shunt and virulence. A screening of a R. fascians mutant library based on the capacity of bacteria to use acetate as the sole carbon source, a metabolic pathway depending on the glyoxylate shunt, resulted in the identification of a new gene essential for R. fascians pathogenicity. This gene encodes a glycosyl transferase, an enzyme known to be involved in the bacterial cell wall biosynthesis but possibly also implicated in cytokinin secretion. A mutant in this gene harboured an altered colony phenotype and could not induce malformations on infected plants. Accordingly, our results were integrated in the leafy gall pathology model recently presented by Stes et al. (2011). Finally, the several questions that are raised by this work, allowed us to suggest further research perspectives in order to unveil a little more of the R. fascians mysterious ways to interact with the plant./Rhodococcus fascians est une bactérie Gram-positive phytopathogène qui induit le développement de galles feuillées, des amplifications locales de multiples bourgeons, sur la plupart des plantes infectées. Ce processus est lié à la production de phytohormones ainsi qu’à la présence de gènes essentiels associés à la virulence tels que les loci plasmidiques att et fas et le gène chromosomique vicA. Cependant, la présence de ces gènes ne suffit pas à garantir le développement du phénotype d’infection, indiquant que d’autres gènes jouent un rôle dans la pathogénicité de R. fascians. Dans ce travail, nous avons étudié les modifications métaboliques qui se produisent lorsque la bactérie interagit avec son hôte par une approche protéomique. Une comparaison entre les souches virulente et avirulente a mis en évidence des variations d’expression au niveau des catalases. Dans la souche virulente, outre l’induction transitoire de l’expression du locus att, la bactérie change son métabolisme pour passer du cycle de Krebs au shunt du glyoxylate, un processus fréquemment observé chez les bactéries confrontées à un environnement hostile. L’expression de l’isocitrate lyase, enzyme spécifique au shunt, augmente, tandis que celle de la fumarate hydratase et de la pyruvate déhydrogénase diminue. Nous nous sommes donc intéressés au lien entre le shunt du glyoxylate et la virulence. Le screening d’une banque de mutants de R. fascians basé sur la capacité de la bactérie à utiliser l’acétate comme seule source de carbone, une voie métabolique dépendant du shunt du glyoxylate, a permis d’identifier un nouveau gène essentiel pour la pathogénicité de R. fascians. Ce gène code pour une glycosyl transferase, une enzyme impliquée dans la biosynthèse de la paroi bactérienne mais également dans la sécrétion des cytokinines. Un mutant dans ce gène présente un phénotype de colonie altéré et ne peut induire de malformations chez les plantes infectées. Finalement, nos résultats et les pistes d’interprétations que nous avons émisent nous permettent de compléter le modèle de l’interaction R. fascians-plante proposé récemment par Stes et al. (2011). Des perspectives de recherches visant une meilleure compréhension de ce pathosystème sont proposées. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Actuellement, le traitement des pathologies infectieuses chez les bovins et les animaux de compagnie est menacé par l’accroissement de l’antibiorésistance et des bactéries multirésistantes. Il est donc primordial pour les entreprises pharmaceutiques vétérinaires de développer de nouvelles gammes d’agents antibactériens spécifiques au domaine animale. Dans ce contexte, il a été montré que certains polyaminostérols naturels tels que la squalamine possèdent un fort potentiel antimicrobien. Ainsi, l’objectif de ce travail de thèse est de répondre à la problématique présentée par la société Virbac dans le traitement des mammites (bovins) et des otites/pyodermites (chien) par le développement d’une nouvelle classe de dérivés polyaminostéroïdiens synthétiques à large spectre antimicrobien. Pour cela, nous avons constitué une chimiothèque de composés originaux préparés à partir de différents acides biliaires selon des voies de synthèse inédites. Ces composés ont été évalués in vitro pour leur cytotoxicité et leurs activités antibactériennes contre diverses bactéries à Gram positif et à Gram négatif et nous avons pu établir la preuve de concept in vitro de leur potentiel thérapeutique en tant qu’agents antibactériens ou adjuvants d’antibiotiques. De plus, nous avons montré que l’un de ces nouveaux dérivés, la claramine A1, agit sur l’intégrité physique des membranes bactériennes et sur les performances d'efflux des pompes AcrAB-TolC. Ainsi, il apparaît finalement que ces dérivés polyaminostéroïdiens au mode d’action non conventionnel pourraient constituer une nouvelle classe d’agents antibactériens pour un usage en tant que substituts d’antibiotiques en médecine vétérinaire. / Currently, the treatment of infectious pathologies in cattle and pets is threatened by the growing antimicrobial resistance and the development of multidrug-resistant bacteria. Thus it is necessary for the veterinary pharmaceutical firms to develop new lines of antibacterial agents. In this context, some natural polyaminosterols such as squalamine have gained interest due to their potent antimicrobial activities. Thus the aim of this PhD work is to provide an answer in the treatment of mastitis (cattle) and otitis/pyoderma (dog) by the development of a new class of synthetic polyaminosterols with a broad spectrum of antibacterial activity. In this purpose, a chemical library of original compounds has been prepared starting from various bile acids by using unprecedented synthesis procedures. These compounds were evaluated for their in vitro cytotoxicity on CHO cells as well as their antibacterial activities against Gram-positive and Gram-negative bacteria and we have establish the in vitro proof of concept of the therapeutic potential of this family of molecules as antibacterial agent or antibiotic adjuvant. Additional investigations were then conducted on one of these novel derivatives namely claramine A1 to deepen knowledge of its mechanism of action and showed that claramine A1 acts on the physical integrity of bacterial membranes and the efflux performance of AcrAB-TolC pumps. Based on the results of claramine A1, it finally appears that these new polyaminosterol derivatives possessing a non-classical mode of action pertain to a new class of antibacterial agents and could constitute a substitute for traditional antibiotics in veterinary medicine.