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      Sex and virulence in Escherichia coli: an evolutionary perspective

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          Abstract

          Pathogenic Escherichia coli cause over 160 million cases of dysentery and one million deaths per year, whereas non-pathogenic E. coli constitute part of the normal intestinal flora of healthy mammals and birds. The evolutionary pathways underlying this dichotomy in bacterial lifestyle were investigated by multilocus sequence typing of a global collection of isolates. Specific pathogen types [enterohaemorrhagic E. coli, enteropathogenic E. coli, enteroinvasive E. coli, K1 and Shigella] have arisen independently and repeatedly in several lineages, whereas other lineages contain only few pathogens. Rates of evolution have accelerated in pathogenic lineages, culminating in highly virulent organisms whose genomic contents are altered frequently by increased rates of homologous recombination; thus, the evolution of virulence is linked to bacterial sex. This long-term pattern of evolution was observed in genes distributed throughout the genome, and thereby is the likely result of episodic selection for strains that can escape the host immune response.

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          Most cited references64

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          MRBAYES: Bayesian inference of phylogenetic trees.

          The program MRBAYES performs Bayesian inference of phylogeny using a variant of Markov chain Monte Carlo. MRBAYES, including the source code, documentation, sample data files, and an executable, is available at http://brahms.biology.rochester.edu/software.html.
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            eBURST: inferring patterns of evolutionary descent among clusters of related bacterial genotypes from multilocus sequence typing data.

            The introduction of multilocus sequence typing (MLST) for the precise characterization of isolates of bacterial pathogens has had a marked impact on both routine epidemiological surveillance and microbial population biology. In both fields, a key prerequisite for exploiting this resource is the ability to discern the relatedness and patterns of evolutionary descent among isolates with similar genotypes. Traditional clustering techniques, such as dendrograms, provide a very poor representation of recent evolutionary events, as they attempt to reconstruct relationships in the absence of a realistic model of the way in which bacterial clones emerge and diversify to form clonal complexes. An increasingly popular approach, called BURST, has been used as an alternative, but present implementations are unable to cope with very large data sets and offer crude graphical outputs. Here we present a new implementation of this algorithm, eBURST, which divides an MLST data set of any size into groups of related isolates and clonal complexes, predicts the founding (ancestral) genotype of each clonal complex, and computes the bootstrap support for the assignment. The most parsimonious patterns of descent of all isolates in each clonal complex from the predicted founder(s) are then displayed. The advantages of eBURST for exploring patterns of evolutionary descent are demonstrated with a number of examples, including the simple Spain(23F)-1 clonal complex of Streptococcus pneumoniae, "population snapshots" of the entire S. pneumoniae and Staphylococcus aureus MLST databases, and the more complicated clonal complexes observed for Campylobacter jejuni and Neisseria meningitidis.
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              Multilocus sequence typing: a portable approach to the identification of clones within populations of pathogenic microorganisms.

              Traditional and molecular typing schemes for the characterization of pathogenic microorganisms are poorly portable because they index variation that is difficult to compare among laboratories. To overcome these problems, we propose multilocus sequence typing (MLST), which exploits the unambiguous nature and electronic portability of nucleotide sequence data for the characterization of microorganisms. To evaluate MLST, we determined the sequences of approximately 470-bp fragments from 11 housekeeping genes in a reference set of 107 isolates of Neisseria meningitidis from invasive disease and healthy carriers. For each locus, alleles were assigned arbitrary numbers and dendrograms were constructed from the pairwise differences in multilocus allelic profiles by cluster analysis. The strain associations obtained were consistent with clonal groupings previously determined by multilocus enzyme electrophoresis. A subset of six gene fragments was chosen that retained the resolution and congruence achieved by using all 11 loci. Most isolates from hyper-virulent lineages of serogroups A, B, and C meningococci were identical for all loci or differed from the majority type at only a single locus. MLST using six loci therefore reliably identified the major meningococcal lineages associated with invasive disease. MLST can be applied to almost all bacterial species and other haploid organisms, including those that are difficult to cultivate. The overwhelming advantage of MLST over other molecular typing methods is that sequence data are truly portable between laboratories, permitting one expanding global database per species to be placed on a World-Wide Web site, thus enabling exchange of molecular typing data for global epidemiology via the Internet.
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                Author and article information

                Journal
                Mol Microbiol
                mmi
                Molecular Microbiology
                Blackwell Publishing Ltd
                0950-382X
                1365-2958
                June 2006
                4 May 2006
                : 60
                : 5
                : 1136-1151
                Affiliations
                [1 ]Department of Molecular Biology, Schumannstraβe 21/22, Max-Planck Institut für Infektionsbiologie 10117 Berlin, Germany
                [2 ]Department of Biology, Lehrstuhl für Zoologie und Evolutionsbiologie, University Konstanz Universitätsstrasse 10, D-78457 Germany
                [3 ]School of Biotechnology and Biomolecular Sciences, University of New South Wales NSW 2052, Australia
                [4 ]The Peter Medawar Building for Pathogen Research, University of Oxford Oxford OX1 3SY, UK
                [5 ]Institut für Mikrobiologie und Tierseuchen, Freie Universität Berlin 10115 Berlin, Germany
                [6 ]Institut für Hygiene, University of Münster 48149 Münster, Germany
                [7 ]School of Molecular and Microbial Biosciences, The University of Sydney NSW 2006, Australia
                [8 ]Department of Biochemistry and Molecular Biophysics, University of Arizona Tucson, AZ 85721, USA
                Author notes
                *For correspondence. E-mail achtman@ 123456mpiib-berlin.mpg.de ; Tel. (+49) 302 846 0751; Fax (+49) 302 846 0750; E-mail thierry.wirth@ 123456uni-konstanz.de ; Tel. (+49) 753 188 2763; Fax (+49) 753 188 2763.
                Article
                10.1111/j.1365-2958.2006.05172.x
                1557465
                16689791
                f0ef7b27-3217-490d-87a5-7a510b6c15d8
                © 2006 The Authors; Journal compilation © 2006 Blackwell Publishing Ltd
                History
                : 22 March 2006
                Categories
                Research Articles

                Microbiology & Virology
                Microbiology & Virology

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