Infection in a dish: high-throughput analyses of bacterial pathogenesis.

Diverse aspects of host-pathogen interactions have been studied using non-mammalian hosts such as Dictyostelium discoideum, Caenorhabditis elegans, Drosophila melanogaster and Danio rerio for more than 20 years. Over the past two years, the use of these model hosts to dissect bacterial virulence mechanisms has been expanded to include the important human pathogens Vibrio cholerae and Yersinia pestis. Innovative approaches using these alternative hosts have also been developed, enabling the isolation of new antimicrobials through screening large libraries of compounds in a C. elegans-Staphylococcus aureus infection model. Host proteins required by Mycobacterium and Listeria during their invasion and intracellular growth have been uncovered using high-throughput dsRNA screens in a Drosophila cell culture system, and immune evasion mechanisms deployed by Pseudomonas aeruginosa during its infection of flies have been identified. Together, these reports further illustrate the potential and relevance of these non-mammalian hosts for modelling many facets of bacterial infection in mammals

C. elegans: an all in one model for antimicrobial drug discovery.

International audienceOne approach to identify new drugs with antimicrobial activities is to screen large libraries of molecules directly for their capacity to block the growth of bacterial or fungal monocultures. A more relevant way to assess both a product's efficacy and its potential cytotoxicity is undoubtedly to use an in vivo infection system. Testing banks containing thousands of natural or chemically synthesized molecules with rodents is generally neither desirable nor feasible. Therefore, invertebrate model organisms could represent a valuable alternative. In this review, we present the worm C. elegans as a suitable host model for the evaluation and characterization of drug effects in a pathogenesis context. This simple organism has been of great value in many fields of biology and is currently intensely used in studies of host-pathogen interactions. Infection of C. elegans induces a number of defense mechanisms, some of which are similar to those seen in mammalian innate immunity. Further, it has been demonstrated that several microbial virulence mechanisms required for full pathogenicity in mammals are also necessary for infection in nematodes. Based on these facts, a number of innovative antimicrobial drug screens have been carried out successfully and the development of new tools to monitor the interaction between worm and microbes in vivo opens promising perspectives

Drosophila larvae food intake cessation following exposure to Erwinia contaminated media requires odor perception, Trpa1 channel and evf virulence factor

International audienceWhen exposed to microorganisms, animals use several protective strategies. On one hand, as elegantly exemplified in Drosophila melanogaster, the innate immune system recognizes microbial compounds and triggers an antimicrobial response. On the other hand, behaviors preventing an extensive contact with the microbes and thus reducing the risk of infection have been described. However, these reactions ranging from microbes aversion to intestinal transit increase or food intake decrease have been rarely defined at the molecular level. In this study, we set up an experimental system that allowed us to rapidly identify and quantify food intake decreases in Drosophila larvae exposed to media contaminated with bacteria. Specifically, we report a robust dose-dependent food intake decrease following exposure to the bacteria Erwinia carotovora carotovora strain Ecc15. We demonstrate that this response does not require Imd innate immune pathway, but rather the olfactory neuronal circuitry, the Trpa1 receptor and the evf virulence factor. Finally, we show that Ecc15 induce the same behavior in the invasive pest insect Drosophila suzukii

Anti-Fungal Innate Immunity in C. elegans Is Enhanced by Evolutionary Diversification of Antimicrobial Peptides

International audienceEncounters with pathogens provoke changes in gene transcription that are an integral part of host innate immune responses. In recent years, studies with invertebrate model organisms have given insights into the origin, function, and evolution of innate immunity. Here, we use genome-wide transcriptome analysis to characterize the consequence of natural fungal infection in Caenorhabditis elegans. We identify several families of genes encoding putative antimicrobial peptides (AMPs) and proteins that are transcriptionally up-regulated upon infection. Many are located in small genomic clusters. We focus on the nlp-29 cluster of six AMP genes and show that it enhances pathogen resistance in vivo. The same cluster has a different structure in two other Caenorhabditis species. A phylogenetic analysis indicates that the evolutionary diversification of this cluster, especially in cases of intra-genomic gene duplications, is driven by natural selection. We further show that upon osmotic stress, two genes of the nlp-29 cluster are strongly induced. In contrast to fungus-induced nlp expression, this response is independent of the p38 MAP kinase cascade. At the same time, both involve the epidermal GATA factor ELT-3. Our results suggest that selective pressure from pathogens influences intra-genomic diversification of AMPs and reveal an unexpected complexity in AMP regulation as part of the invertebrate innate immune response

Inducible antibacterial defense system in C. elegans.

International audienceThe term innate immunity refers to a number of evolutionary ancient mechanisms that serve to defend animals and plants against infection. Genetically tractable model organisms, especially Drosophila, have contributed greatly to advances in our understanding of mammalian innate immunity. Essentially, nothing is known about immune responses in the nematode Caenorhabditis elegans. Using high-density cDNA microarrays, we show here that infection of C. elegans by the Gram-negative bacterium Serratia marcescens provokes a marked upregulation of the expression of many genes. Among the most robustly induced are genes encoding lectins and lysozymes, known to be involved in immune responses in other organisms. Certain infection-inducible genes are under the control of the DBL-1/TGFbeta pathway. We found that dbl-1 mutants exhibit increased susceptibility to infection. Conversely, overexpression of the lysozyme gene lys-1 augments the resistance of C. elegans to S. marcescens. These results constitute the first demonstration of inducible antibacterial defenses in C. elegans and open new avenues for the investigation of evolutionary conserved mechanisms of innate immunity

Cytosolic and Secreted Peptidoglycan-Degrading Enzymes in Drosophila Respectively Control Local and Systemic Immune Responses to Microbiota

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