infection and immunity(modified)

1Chapter6BacteriaInfection2ThischapterfocusesonDefinitionsnormalflora,opportunisticpathogen,dysbacteriosis,nosocomialinfection,bacteremia,septicemia,pyemia,toxemia,carrierQuestionsUnderwhatconditionsdoopportunisticpathogenscausediseases?Whatfactorsareassociatedwithpathogenicityofpathogens?Whatdothevirulencefactorsofpathogensinclude?Whatisthedifferencebetweenendotoxinsandexotoxins?BacteriaNormalfloraOpportunisticpathogenPathogenSection1NormalfloraandOpportunisticpathogen4NormalfloraDefinitionMicroorganismsthatliveonorinhumanbodies,andordinarilydonotcausehumandiseasesThevariousbacteriaandfungithatarepermanentresidentsofcertainbodysites,especiallytheskin,oralcavity,colonandvagina,usuallydonotcauseanyproblemsforthehostbody.5NormalfloraMedicalSignificanceAntagonismMechanism•Competitionforreceptorsonhostcells•Competitionfornutrients•MetabolicortoxicproductsNutritionalfunctionseveralBvitaminsandvitaminKImmunitynormalflorasharemanyantigenicdeterminantswithpathogenicorganisms6OpportunisticpathogensDefinitionnormallynonpathogenicmicroorganismscapableofcausinginfectiondiseaseundercertainconditions.ConditionsAlterationofcolonizationsitesDeclinationofthehostimmunitydefenseDysbacteriosisDefinition:thestateinwhichtheproportionofbacterialspeciesandthenumberofthenormalfloracolonizinginacertainsiteofahostpresentlarge-scalealteration.Result:Itoftenleadtosuperinfection.PathogenicityTheabilityofaninfectiousagenttocausedisease.Aqualitativetermthatrefertoanorganism'sabilitytocausediseaseVirulenceAquantitativemeasurementofpathogenicityVirulenceinvolvesinvasionandtoxigenicity.ID50:Infectiousdosefor50%ofthetestpopulationLD50:Lethaldose(ofatoxin)for50%ofthetestpopulationSection2BacterialPathogenesisImportantfactorsofpathogenicityVirulenceofbacteriaTheamountofentryTheportalofentryPathogenicityofpathogens9VirulenceInvasivenessDefinition:Theabilityofamicroorganismtocolonize,invadeandspreadthroughthehost.Toxin10InvasivenessAdherencefactorsPiliNeisseriagonorrhoeaeOthersurfacestructuresLTACapsulesandslimelayersStreptococcuspneumoniae11InvasivenessInvasiveenzymesHyaluronidase:hyaluronicacidCoagulaseCollagenase12ToxinExotoxinEndotoxin13ExotoxinOriginGram-positivebacteria(most)Gram-negativebacteriaReleaseSecretedbylivingbacteria(most)Releaseduponbacteriallysis14ExotoxinPhysicalandchemicalpropertiesPolypeptideHeat-labile:60-80℃,30min15ExotoxinImmunity:BeneutralizedbyAntibodies(anti-toxins)AntitoxinDefinition:aspecificantibodycapableofneutralizingtheexotoxinthatstimulatesitsproduction.Application:treatmentorurgentpreventionmeasureToxoidDefinition:amodifiedexotoxinthathasbeentreatedtodestroyitstoxicityandremainsimmunogenicity.Application:vaccinetoxoidtoxinHorseserumantitoxinhypersensitivityantibodyantigen17ExotoxinToxicityHighTissuespecificity18ExotoxinThreetypesNeurotoxinTetanustoxin,clostridiumtetani,rigidparalysisEnterotoxinv.choleraedisturbtheprocessesthatregulateionandwaterexchangeacrosstheintestinalepitheliumCytotoxindiphtheriatoxininhibitsproteinsynthesisopisthotonos19A-BtoxinsActiveBindingACellsurfaceB20EndotoxinOriginandreleaseGram-negativebacteriaReleasedonlywhenbacterialyseChemicalandphysicalpropertiesLipopolysaccharide(LPS)heat-stable:160℃,2-4hrs21Endotoxin22EndotoxinImmunityweaknotoxoidavailable23EndotoxinBiologicactivityWeakSimilarbiologicaleffectsFever(IL-1,TNF)LeukocytereactionEndotoxicshockDIC(disseminatedintravascularcoagulation)24PropertiesExotoxinendotoxinOriginG+andG-G-ReleaseSecretedfromlivingcellsorreleaseduponbacteriallysisReleaseduponbacteriallysiscompositionProteinLPSHeat-resistanceSensitiveResistanceImmunityHigh,antitoxin,toxoidLow,notoxoidToxicityHigh,tissuespecificityLow,notissuespecificityThedifferencesbetweenexotoxinandendotoxin25VirulenceVirulencefactorsinvasivenesstoxinAdherencefactorexotoxinendotoxinInvasiveenzymeCapsuleandslimelayer26PathogenicityTheamountofentryspeciesofbacteriaHostdefensestate27PathogenicityTheroutesofentrySkinRespiratorytractGastrointestinaltractUrogenitaltrackMultipleroutes28SourcesofinfectiousdiseasesExogenousinfectionsPatientsCarriersThoseinwhompathogensmultiplyandmaybetransmittedtootherindividuals,butwhoshowsnoclinicalfindingstotheirpresence.ConvalescentcarriersandHealthycarriersInfectedanimalsEndogenousinfectionscausedbyopportunisticpathogensamongnormalfloraNosocomialinfectionsSection3InitiationandCourseofInfection29SourcesofinfectiousdiseasesNosocomialinfectionsDefinitions:infectionsacquiredinahospital.Alsocalledhospital-acquiredinfections.SourcesEndogenousinfectionsCrossinfectionsInappropriatehospitalproceduresHospitalprocedurepatientHospitalpersonnel,visitors,orotherpatients30ModesoftransmissionRespiratoryinfectionsGastrointestinalinfectionsTraumainfectionsContactinfectionsAnimalbiteinfections31TypesofinfectionsDeterminantsofinfectionsPathogenicityofbacteriaImmunitydefenseofhostsEnvironmentalfactorsInapparentinfectionApparentinfection32InapparentinfectionSubclini