title: Genomic characterization of a large outbreak of Legionella pneumophila serogroup 1 strains in Quebec City, 2012.
abstract: During the summer of 2012, a major Legionella pneumophila serogroup 1 outbreak occurred in Quebec City, Canada, which caused 182 declared cases of Legionnaire's disease and included 13 fatalities. Legionella pneumophila serogroup 1 isolates from 23 patients as well as from 32 cooling towers located in the vicinity of the outbreak were recovered for analysis. In addition, 6 isolates from the 1996 Quebec City outbreak and 4 isolates from patients unrelated to both outbreaks were added to allow comparison. We characterized the isolates using pulsed-field gel electrophoresis, sequence-based typing, and whole genome sequencing. The comparison of patients-isolated strains to cooling tower isolates allowed the identification of the tower that was the source of the outbreak. Legionella pneumophila strain Quebec 2012 was identified as a ST-62 by sequence-based typing methodology. Two new Legionellaceae plasmids were found only in the epidemic strain. The LVH type IV secretion system was found in the 2012 outbreak isolates but not in the ones from the 1996 outbreak and only in half of the contemporary human isolates. The epidemic strains replicated more efficiently and were more cytotoxic to human macrophages than the environmental strains tested. At least four Icm/Dot effectors in the epidemic strains were absent in the environmental strains suggesting that some effectors could impact the intracellular replication in human macrophages. Sequence-based typing and pulsed-field gel electrophoresis combined with whole genome sequencing allowed the identification and the analysis of the causative strain including its likely environmental source.
authors.affiliation: Laboratoire de Santé Publique du Québec (LSPQ)/Institut National de Santé Publique du Québec, Québec, Canada.
authors.forename: Simon
authors.initials: S
authors.lastname: Lévesque
authors.affiliation: Université Laval, Department of Molecular Medicine, Québec, Canada.
authors.forename: Pier-Luc
authors.initials: PL
authors.lastname: Plante
authors.affiliation: Department of Natural Resource Sciences, Faculty of Agricultural and Environmental Sciences, McGill University, Québec, Canada.
authors.forename: Nilmini
authors.initials: N
authors.lastname: Mendis
authors.affiliation: Centre d'Expertise en Analyse Environnementale du Québec, Québec, Canada.
authors.forename: Philippe
authors.initials: P
authors.lastname: Cantin
authors.affiliation: Institut de Recherche Robert-Sauvé en Santé et en Sécurité du Travail, Québec, Canada.
authors.forename: Geneviève
authors.initials: G
authors.lastname: Marchand
authors.affiliation: Laboratoire de Santé Publique du Québec (LSPQ)/Institut National de Santé Publique du Québec, Québec, Canada; Département de Microbiologie, Immunologie et Infectiologie, Université de Montréal, Québec, Canada.
authors.forename: Hugues
authors.initials: H
authors.lastname: Charest
authors.affiliation: Université Laval, Department of Molecular Medicine, Québec, Canada.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Raymond
authors.affiliation: Direction Régionale de Santé Publique de la Capitale-Nationale, Québec, Canada.
authors.forename: Caroline
authors.initials: C
authors.lastname: Huot
authors.affiliation: Direction Régionale de Santé Publique de la Capitale-Nationale, Québec, Canada.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Goupil-Sormany
authors.affiliation: Direction Régionale de Santé Publique de la Capitale-Nationale, Québec, Canada.
authors.forename: François
authors.initials: F
authors.lastname: Desbiens
authors.affiliation: Department of Natural Resource Sciences, Faculty of Agricultural and Environmental Sciences, McGill University, Québec, Canada.
authors.forename: Sébastien P
authors.initials: SP
authors.lastname: Faucher
authors.affiliation: Université Laval, Department of Molecular Medicine, Québec, Canada.
authors.forename: Jacques
authors.initials: J
authors.lastname: Corbeil
authors.affiliation: Laboratoire de Santé Publique du Québec (LSPQ)/Institut National de Santé Publique du Québec, Québec, Canada; Centre de Recherche du Centre Hospitalier de l'Université de Montréal, Québec, Canada.
authors.forename: Cécile
authors.initials: C
authors.lastname: Tremblay
mesh_terms: D001483:Base Sequence; D018441:Biofilms / Q000254:growth & development; D016000:Cluster Analysis; D019295:Computational Biology; D004196:Disease Outbreaks; D016521:Electrophoresis, Gel, Pulsed-Field; D016680:Genome, Bacterial / Q000235:genetics*; D049674:History, 21st Century; D006801:Humans; D016952:Legionella pneumophila / Q000235:genetics*; D007877:Legionnaires' Disease / Q000453:epidemiology*; D008969:Molecular Sequence Data; D010802:Phylogeny; D011792:Quebec / Q000453:epidemiology; D017422:Sequence Analysis, DNA; D018709:Statistics, Nonparametric
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