evolution and ecology of pathogens课件

EvolutionandEcologyofPathogens MartinPolzCivil EnvironmentalEngineeringMassachusettsInstituteofTechnology Outline EmergenceofpathogensGlobalimportanceofmicroorganismsWhatarepathogens EvolutionofpathogenesisRe emergenceofpathogensAntibioticresistanceCholeraConclusions Germs germseverywhereEvenonalittlepear Germsgermsallaround Evenonthedirtyground Germs germsmakemesick Especiallyonacandystick Germs germsaresosmall Evenonabouncyball Candice sGermPoem Microbialcommunitiesdrivebiogeochemicalcycles 100humanactivities 140biologicalfixation 200denitrification SOIL ATMOSPHERE OCEANS 15biologicalfixation 140denitrification 1200internalcycling 8000internalcycling 10burial 36riverflow 3fixationinlightening groundwater Example TheNitrogenCycle humanactivities 140biologicalfixation 200denitrification SOIL ATMOSPHERE OCEANS 15biologicalfixation 140denitrification 1200internalcycling 8000internalcycling burial riverflow 3fixationinlightening groundwater NitrogenCycleWithoutMicrobes Allprocessesslow Wouldlifebepossible Microbes BacteriaFungiProtistsViruses Bacteria SmallEfficientBiochemicallydiverseFastgrowth Whitmanetal 1998 Bacteriaareeverywhere Globalbacterialbiomass PgofC Microbialbiomassrivalsplantbiomassbuthashigherturnover Howmanybacterialspeciesarethere Wilson1988 Totalnumberspecies 1 4millionBacteria 3 500 Hammond1995 Totalnumberspecies 11millionBacteria 10million Thegreatplatecountanomaly DAPIstainedmarinewatersample 1 ofobservablebacteriagrowonstandardculturemedia Geneticdiversity Totalnucleicacids 16SribosomalRNAgenes Sequences Diversityandevolutionaryrelationships Identificationandquantification Molecularapproach greatdiversityofmicrobespathogensonlyaminorcomponentofmicrobialdiversityallowsunderstandingofevolutionofpathogenesis Emergenceofpathogens Whatisapathogen Anevolutionaryview Example Escherichiacoli E coli Normallyaharmlessgutbacteriumbut EterotoxigenicstrainsEnteropathogenicstrainsEnteroinvasivestrainsEnterohemorrhagicstrainsEnteroaggregativestrainsUropathogenicstrains Genomeanalysisprovidesanswer StrainscloselyrelatedGenomestructuresimilarBut Insertionsof foreign DNA pathogenicityislands Comparativeanalysis ComparisonharmlessandpathogenicE colistrains A B A B C C E coliK12 E coliO157 H7 ForeignDNA locusofenterocyteeffacementResponsibleforpathogenicity allowsattachmentandtoxinproductions Aharmlessbacteriumhasbecomeapathogenby stealing DNAfromanotherbacterium Mechanismsofgenetransfer Transformation uptakeofDNAfromenvironmentTransduction DNAtransferbyvirusesConjugation plasmidtransferbetweenbacterialcells 1 2 3 Canalltransfergenesfromotherbacteriathatcanbecomeincorporatedintogenome Fateoftransferredgenes RecAsystem recombinationintogenomedependentonsequencesimilarity sequencedifference recombinationrate Howoftendoesgenetransferhappen Genetransferisraree g transductionbyvirusesinsertforeignDNAevery108virusinfectionsBut Microbeshaveverylargepopulationse g genetransferinmarineenvironment 20millionbilliontimespersecond Genesmustbeadvantageoustorecipient Ecologyofpathogenesis BacteriagrowfastHighpopulationdensitiesGreatcompetitionforresources Pathogen normalbacteriumthathasgainedaccesstoanewresourcethroughnewgenes Competitiveadvantage Re emergenceofpathogens Example1 Antibiotics Antibiotics naturalwarfare Example1 Antibiotics Antibiotics naturalwarfare commonresource species1 species2 antibiotic Example1 Antibiotics Antibiotics naturalwarfare commonresource species1 species2 antibiotic Example1 Antibiotics Antibiotics naturalwarfare commonresource species1 Antibioticresistance BacteriahaveevolvedresistancegenestoantibioticsLocatedonplasmids Plasmidencodedresistanceiseasilytransferredbetweenspeciesbecauseplasmidsaremobile Occurrenceusuallylowunlessselectionthroughwidespreadantibioticuse Antibioticsoverusecreates Superbugs 50milliontonsantibioticsperyear Superbugs resistanttomostantibioticsExample Tuberculosis2 5milliondeathsMycobacteriumtuberculosisincreasinglyresistant Example2 Choleraandclimate Vibriocholeraeandothervibriosubiquitousinmarine coastalwatersGeneticallysimilarnon pathogenicandpathogenicstrainsco exist V cholera Vibriospeciesidentifiedasagentsofhumandisease SeasonalcholerainCalcutta Sharma 1998 VibrioinfectionslinkedtoElNino Dhaka BangladeshCholeracasesSeasonalityRemoved Pascual 2000 Attachmenttoalgaeandzooplankton Temperaturedependentgrowth Possiblereasonsforseasonality Algalgrowth vibriogrowth T Temperaturerise vibriogrowth Linkstoglobalwarmingand orpollution Conclusions Re Emergenceisanevolutionary ecologicalphenomenonMicrobialcommunitiesextremelydiverseLargenumbersofindividualsPotentialforgenetransferPathogenesisarisesviagenetransferResult harmlessbacterialspeciesbecomespathogenbecauseitgainscompetitiveadvantageEcologicalfactors resistance alternatehosts climate maytriggerincreasedincidenceofpathogenesis OutlookforthefutureNeedtoundersta