%0 Journal Article %T Spontaneous Loss of Virulence in Natural Populations of Listeria monocytogenes %+ Centre collaborateur de l'OMS Listeria / WHO Collaborating Centre Listeria (CC-OMS / WHO-CC) %+ Centre National de Référence Listeria - National Reference Center Listeria (CNRL) %+ University of Edinburgh %+ Biologie des Infections - Biology of Infection %+ Interactions Bactéries-Cellules (UIBC) %+ Université Paris Descartes - Paris 5 (UPD5) %+ CHU Necker - Enfants Malades [AP-HP] %+ Imagine - Institut des maladies génétiques (IHU) (Imagine - U1163) %A Maury, Mylène, M %A Chenal-Francisque, Viviane %A Bracq-Dieye, Hélène %A Han, Lei %A Leclercq, Alexandre %A Vales, Guillaume %A Moura, Alexandra %A Gouin, Edith %A Scortti, Mariela %A Disson, Olivier %A Vazquez-Boland, Jose %A Lecuit, Marc %Z Work in M.L.'s laboratory was supported by Institut Pasteur, Inserm, LabEx IBEID, the European Research Council, and Santé Publique France. Work in J.A.V.-B.'s laboratory was supported by the Wellcome Trust (program grant WT074020MA) and partially by core Roslin Institute funding from BBSRC (BB/J004227/1) %< avec comité de lecture %@ 0019-9567 %J Infection and Immunity %I American Society for Microbiology %V 85 %N 11 %P e00541-17 %8 2017-10-18 %D 2017 %R 10.1128/IAI.00541-17 %M 28827366 %K virulence %K Listeria monocytogenes %K hemolysis %K genomics %K spontaneous mutations %Z Life Sciences [q-bio]/Human health and pathology %Z Life Sciences [q-bio]/Human health and pathology/Infectious diseases %Z Life Sciences [q-bio]/Microbiology and Parasitology/Bacteriology %Z Life Sciences [q-bio]/Microbiology and ParasitologyJournal articles %X The pathogenesis of Listeria monocytogenes depends on the ability of this bacterium to escape from the phagosome of the host cells via the action of the pore-forming toxin listeriolysin O (LLO). Expression of the LLO-encoding gene (hly) requires the transcriptional activator PrfA, and both hly and prfA genes are essential for L. monocytogenes virulence. Here, we used the hemolytic activity of LLO as a phenotypic marker to screen for spontaneous virulence-attenuating mutations in L. monocytogenes. Sixty nonhemolytic isolates were identified among a collection of 57,820 confirmed L. monocytogenes strains isolated from a variety of sources (0.1%). In most cases (56/60; 93.3%), the nonhemolytic phenotype resulted from nonsense, missense, or frameshift mutations in prfA. Five strains carried hly mutations leading to a single amino acid substitution (G299V) or a premature stop codon causing strong virulence attenuation in mice. In one strain, both hly and gshF (encoding a glutathione synthase required for full PrfA activity) were missing due to genomic rearrangements likely caused by a transposable element. The PrfA/LLO loss-of-function (PrfA Ϫ /LLO Ϫ) mutants belonged to phylogenetically diverse clades of L. monocyto-genes, and most were identified among nonclinical strains (57/60). Consistent with the rare occurrence of loss-of-virulence mutations, we show that prfA and hly are under purifying selection. Although occurring at a low frequency, PrfA Ϫ /LLO Ϫ muta-tional events in L. monocytogenes lead to niche restriction and open an evolutionary path for obligate saprophytism in this facultative intracellular pathogen. %G English %Z We acknowledge Anne Morvan, Thomas Cantinelli, Nathalie Tessaud-Rita and Laetitia Bellon for their help in strain collection and isolation at the National Reference Centre for Listeria. We thank Pascale Cossart for providing antibodies against LLO and the Institut Pasteur P2M platform for genome sequencing. %2 https://pasteur.hal.science/pasteur-02168452/document %2 https://pasteur.hal.science/pasteur-02168452/file/e00541-17.pdf %L pasteur-02168452 %U https://pasteur.hal.science/pasteur-02168452 %~ INSERM %~ PASTEUR %~ UNIV-PARIS5 %~ INRA %~ APHP %~ USPC %~ AGREENIUM %~ CHU-UNIV-PARIS5 %~ INRAE %~ UNIV-PARIS %~ UP-SANTE %~ ANR %~ BIOLOGY-INFECTION %~ CNR-LISTERIA %~ UA000005