Listeria monocytogenes | EPFL Graph Search

Listeria monocytogenes is the species of pathogenic bacteria that causes the infection listeriosis. It is a facultative anaerobic bacterium, capable of surviving in the presence or absence of oxygen. It can grow and reproduce inside the host's cells and is one of the most virulent foodborne pathogens: 20 to 30% of foodborne listeriosis infections in high-risk individuals may be fatal. In the European Union, listeriosis follows an upward trend that began in 2008, causing 2,161 confirmed cases and 210 reported deaths in 2014, 16% more than in 2013. Listeriosis mortality rates are also higher in the EU than for other foodborne pathogens. Responsible for an estimated 1,600 illnesses and 260 deaths in the United States annually, listeriosis ranks third in total number of deaths among foodborne bacterial pathogens, with fatality rates exceeding even Salmonella spp. and Clostridium botulinum. Listeria monocytogenes is a Gram-positive bacterium, in the phylum Bacillota, named after Joseph Lis

Mechanism of DegU-dependent activation of flagellar gene transcription in Listeria monocytogenes

Diane Baer

Flagellar motility is an important process for bacterial survival. It allows bacteria to move to aquire nutrients or to retreat from unfavorable environments. In the Gram-positive bacterium Listeria monocytogenes, flagellar motility is a temperature-dependent process, being restricted to temperatures below 37°C. This regulation is mediated by the activities of the DegU response regulator, the MogR transcriptional repressor and GmaR, the MogR antirepressor. Transcriptional regulation of the fliN-gmaR promoter is central to flagellar motility regulation as pfliN-gmaR is transcriptionally activated by DegU and is also MogR repressed. However, the mechanism by which DegU mediates transcriptional activation of the fliN-gmaR promoter is not well understood. In this study, we further investigated the mechanisms controlling transcription initiating at the fliN-gmaR promoter by performing two comprehensive transposon mutagenesis screens to identify any additional factors involved in the activation and repression of pfliN-gmaR. The mutagenesis screen performed at 30°C to identify factors involved in pfliN-gmaR transcriptional activation led to the identification of a novel factor. We demonstrated that Lmo0866, a protein from the DEAD-box protein family, is required for transcriptional activation of pfliN-gmaR and therefore flagellar motility. Moreover, we identified CodY as being involved in the repression of pfliN-gmaR at 37°C.

2010

Impact de l'exploitation des alpages sur la qualité des eaux

Agricultural fertiliser (farmyard manure), covers partially the nutrient elements demand of the vegetation cover. However, its application is difficult as regards the unknown concentration of fertilising elements contained and their biological availability for the plants, the important volumetric masses to manage and the general uneven land application. An inaccurate management of farmyard manure may cause groundwater pollutions with sometimes serious consequences, especially in the case of karst aquifers. The objective of this research was to specify various aspects of the farmyard manure cycle. It consists of three major parts: a general study of the difficulties related to the farmyard manure management in mountainous regions with the aim to provide practical recommendations to reduce the risk of groundwater contaminations, the evaluation of an alternative method of pig farming in liberty the study of the impacts of agricultural activities on the surface- and groundwater quality. Based on the analysed farmyard manure managements, the following practical recommendations have been made: split up the land application, but concentrate the input of nutrient elements in spring, during the period of plant growth. For sanitary reasons, a delay of at least 1 month has to be respected between the last land application and the beginning of pasture; collect in adequate installations all agricultural effluents which potentially cause water pollution, except if they are spread out immediately. minimise the production of fertiliser by the following two possibilities: infiltrate low contaminated waste water (from the roof, spring, eventually from the farm) reduce the time the animals stay in the stable. An alternative method of pig farming in liberty has been tested in the field. 25 pigs have been raised on a field of ca. 2 ha, representing a density of 0.71 LiveStock Unit/ha/y, respectively 0.18 LSU/ha/m during 4 months. Amongst others, the study has considered the impacts of pig pasture on the environment (vegetation cover, soil) and the animals health. The most important impact is in fact the destruction of the vegetation cover, with its direct repercussions on the botanical diversity and the concentration of nutrients in the soil. The experiment has made evident the importance to keep the vegetation cover intact, in order to adsorb the nutrient elements in the manure. An advantageous method to reduce the impacts on the vegetation cover is to equip the pigs with nose-rings. It is furthermore necessary to altemate the pasture parks in order to enable the vegetation to recover (2 to 3 different parks). The important impacts observed around the pig feeding through can be avoided by two ways: first, by changing the throughs placement during the pasture period or second, by the construction of a concrete place and the collection of the manure in the slurry pit. For the pasture of pigs in liberty one has to chose grasslands with thick soils of good quality but avoid oligotrophic ones. Cattle sheds and feeding through have to be placed in a manner to favour a maximum dispersion of the animals. Two hydrogeological observation networks, composed of 6 springs, 7 rivers and one lake, have been installed in order to study the potential contamination by pathogenic bacteria (Listeria, Campylobacter, Yersinia, Salmonella). No salmonella have been found, but several other species have been identified in the water samples of the different study sites: Campylobacter jejuni, C. coli, C. fetus Listeria monocytogenes (sv 1 /2a, 1/2b, 4b), L. ivanovii ivanovii (sv 5) Yersinia intermedia, Y. frederiksenii, Y. enterocolitica, Y. kristensenii, Y. pseudotuberculosis. The most frequently identified species in the studied sites is C. jejuni. It has been isolated in 75% of the sites, with an average percentage of isolation of 11% of' the spring samples, 22% of the river and 56% of the lake samples. L. monocytogenes has been isolated several times in 9 of the 14 sites. It is less abundant than C. jejuni, except in the analysed springs. The presence of C. jejuni and L. monocytogenes 4b has shown to be closely related to the summer pasturing period. Other germs, like L. monocytogenes 112a and yersinias show a uniform annual distribution. The presence of bacteria in surface and groundwater is controlled by several factors, of which the presence of animals, precipitation and temperature have been identified to be the most conclusive ones. In case of source contamination, the factors controlling the presence or absence of pathogen bacteria are different for the case of surface and groundwater: In the first case, the influences of the hydroclimatological conditions are dominant, whereas in the second case it is controlled mainly by the local hydrogeological characteristics. In case of aquifers with interstitial porosity (Clos Ister, Confluent), the presence of pasturing anirnals is however the controlling factor. The persistence of a contamination is controlled by the storage capacity of the catchment basin and by the relation of seep water to the aquifer total volume. In the Brassus spring case, the presence of animals on the catchment area can not explain by itself the bacteriological findings. The presence of the found pathogen bacteria can however be explained by their transport by the run-off rain. The presence of pathogen germs and bacterial pollution indicators has been analysed in a comparative study. Result: 2.3% of the samples contained pathogen germs without containing bacteriological contamination indicator. The species found in the absence of bacterial pollution indicators, are rare species, showing a monotonous annual occurrence. They have been found only in low concentration and the danger when drinking this contaminated water was very small. That means the bacterial pollution indicators choice presently used for water bacteriological quality evaluation is accurate. However, they should be tested with high flow levels, when bacteriological contaminations are particularly important.

EPFL1999

Protein engineering approaches for direct antigen targeting in CD8+ T cell inducing vaccines

Vasiliki Panagiotou

Effective vaccine design and public vaccination programs have led to the eradication of several diseases and protected millions of people from deadly infections. However, intracellular infections remain a challenge and their eradication requires the activation of cytolytic mechanisms. CD8+ T cells promote effector mechanisms for infected cell killing subsequent to their priming by antigen-presenting cells. Their activation occurs upon detection of intracellular antigen in a pathway that many current subunit vaccine technologies are trying to approach by cross-presentation. Advances in CD8+ T cell-inducing subunit vaccines include direct targeting of antigens to cross-presenting cells and are studied in this thesis. Antigen delivery to the appropriate cell type for cross-presentation to CD8+ T cells can occur with fusion antibodies. Our laboratory has previously demonstrated that antigens bearing an erythrocyte-binding antibody domain (TER119) target the liver. We used this technology to fuse TER119 and ovalbumin (OVA) antigen with the BBOX domain of the high mobility group box 1 (HMGB1) danger signal and co-administer it with CpG-B adjuvant in a hepatic vaccine context. In liver vaccines, activation of local cytotoxic responses represents an important challenge. Erythrocyte-mediated OVA delivery with adjuvants resulted in cytotoxic CD8+ T lymphocyte (CTL) activation with memory formation in the liver and protection was provided after infection with Listeria monocytogenes. Another method for antigen targeting is through a cross-presenting dendritic cell (DC) subset, called CD8+ DCs. Recent studies in mice showed successful vaccination against OVA fused to XCL1 ligand, which binds CD8+ DCs. To attract CD8+ DCs to the site of injection for increased antigen uptake, we co-injected XCL1-OVA with a fusion protein consisting of XCL1 and the extracellular matrix (ECM) binding domain of placenta growth factor-2 (PlGF-2123-144), called XCL1-PlGF. XCL1-PlGF binds extracellular matrix at the injection site and attracts CD8+ DCs locally. In the context of prophylactic and therapeutic vaccination, the combination of two fusion proteins (XCL1-OVA and XCL1-PlGF) enhanced cytotoxicity and prolonged survival against B16-OVA melanoma. Finally, antigen transport via biomaterial delivery platforms was evaluated as an alternative method to deliver antigens to immunologically relevant sites. Our laboratory and others have shown that nanoscale carriers promote CTL responses in vaccination. Here we present a cationic micelle vaccination platform in which OVA and adjuvant (CpG-B and/or MPLA) loading is mediated by non-covalent molecular encapsulation and adsorption. Following a prime and double boost vaccination, CTL responses were raised in the spleen and lymph nodes of vaccinated mice, along with antigen-specific antibody production. These findings highlight the advantages of the micelle carrier platform in vaccine applications. Overall, this thesis presents novel techniques to target antigens to the appropriate cell compartments, facilitating CTL activation in vaccination either by direct targeting of antigen fused to antibodies and chemokines, or antigen delivery with polymeric vehicles. These platforms for optimized delivery seek to improve current approaches and impact the design of new strategies in CD8+ T cell inductive vaccination.

EPFL2016