BacterialInfectionBacterialInfectionNormalfloraOpportunisticpathogenPathogenicbacteria(virulentbacteria)DysbacteriosisExotoxinsEndotoxinsSeparation&CultureofbacteriaBacteriemiaSepticemiaPyemiaToxemiaEndotoxemiaCarrierColonyToxoidsAntitoxinKeyWordsNormalfloraBacteriemiaKeyWoNotallbacteriacausediseaseNormalflora–

Thenormalfloraarebacteriawhicharefoundinoronourbodiesonasemi-permanentbasiswithoutcausingdisease.Therearemorebacterialivinginoronourbodies,thanwehavecellsofourown.Ahumanbodycontainsaround1013

cells.Thehumanbodyishometoaround1014bacteria.Onefourthoffecalweightismadeofbacteria!Thenormalfloraareparticularlyimportantinthelargeintestine.

Normalfloraarealsofoundinthe

nose,mouth,throat,skin.Opportunisticbacteria–canbepartofthenormalflorabut

notpathogenicfornormalpersons,causediseaseonlyinimmunocompromisedpersons,orunderspecificconditions.Pathogenicbacteria(virulentbacteria)–Normallynotmembersofthenormalflora,

havemechanismstopromotetheirowngrowthintheexpenseofhost’stissueororgan’sfunctionNotallbacteriacausediseaseThenormalfloraprotectusfromdiseaseby:

1.Competingwithinvadersforspaceandnutrients.2.Producingcompounds(bacteriocins)whichkillotherbacteria.3.LoweringthepHsothatotherbacteriacan'tgrow.ThenormalfloraprotectusfrInadditiontotheabovewaysofprotectingusfromdiseaseournormalflorahelpusinotherways.Ofcourse,thereisadownsideaswell...TheGoodSideProducevitaminsweareunabletoproducesuchasvitaminB12.Boostourimmunesystem—Germfreeanimals(bornandraisedinagermfreeplastictent)areverysusceptibletodiseasewhenremovedfromthegermfreeenvironmentbecausetheirimmunesystemisunderdeveloped.Helpdigestfood.InadditiontotheabovewaysTheBadSideIfthenormalfloraescapefromtheirnormallocation,theycancausedisease.Forexample,

Escherichiacoli,commonlyfoundintheintestine,cancauseurinarytractinfectionsifintroducedintothebladder.Immunosuppressioncanallowotherwiseharmlessbacteriatocausedisease.AIDS,somecancertreatmentsandtransplantrejectiondrugsallsuppresstheimmunesystemandallowthenormalfloratocauseoccasionallyseriousdisease.TheBadSide

Threeconditionscorrelatewithopportunisticinfection:1.ImmuneSystemCompromise2.Dysbacteriosis3.ChangeofInhabitingPlaces:ThreeconditionscorrelatewiPathogenesisisamulti-factorialprocesswhichdependsonthenatureofthespeciesorstrain(virulencefactors),thePathwayofBacterialEntrance(gateway)andtheimmunestatus

ofthehost,aswellasthenumberoforganismsintheinitialexposureandtheEnvironmentalconditions.

BacterialPathogenesisPathogenesisisamulti-factorBACTERIALVIRULENCEFACTORS

BACTERIALVIRULENCEFACTORSAdherenceFactorsSurfacehydrophobicity,pili,Capsule&glycocalyxBacterialBiofilmsInvasionofHostCells&Tissues:Enzymesimmuneevasion:

Capsule&glycocalyx,

IgA1Proteases,Antigenicvariation,InterferenceofcomplementactivityIntracellularpathogenicityⅠ.BacterialVirulenceFactorsAdherenceFactorsⅠ.Bacterial4.Toxins

ExotoxinsEndotoxinsExotoxins

proteins

usuallyenzymesdestroycellularstructuresdestroyextracellularmatrixAntibodies(anti-toxins)neutralize----vaccinationActiveBindingACellsurfaceBA-Btoxins4.Toxins

ExotoxinsExotoxinsACholeratoxinandE.colilabiletoxinADP-ribosylationofregulator

adenylatecyclaseactivationcyclicAMPactiveionandwatersecretion

diarrheaCholeratoxinandE.colilabiTetanustoxininhibitsglycinerelease

inactivatesinhibitoryneuronsmusclesover-active

rigidparalysis

NormalconditionRigidparalysisTetanustoxinNormalconditionR

Botulinumtoxininhibitsacetylcholinereleaseinhibitsnerveimpulsesmusclesinactiveflacidparalysis(Acetylcholine)Botulinumtoxin(Acetylcholine15ExotoxinsAntibodies(anti-toxins)neutralizevaccination15ExotoxinsAntibodies(anti-toEndotoxins

Lipopolysaccharide(LPS):

atoxiclipidA

acorepolysaccharide

Oantigenpolysaccharidesidechains

CellwalllysisrequiredFormaldehydeandheatresistantPoorantigenasfreemoleculeEndotoxineffects

EndotoxinsLipopolysaccharide

Endotoxineffects

Fever-pyrogen1microgram/kgLeukopeniaandleukocytosisnecrosisEndotoxemiaandshockDisseminatedintravascularcoagulation(DIC).Non-specificinflammation.CytokinereleaseComplementactivationBcellmitogensPolyclonalBcellactivatorsAdjuvantsEndotoxineffectsNon-speci細(xì)菌的感染診斷防治消毒滅菌Exotoxins

Toxinsproducedbybacteriaandsecretedtotheoutsideofthebacteriacell(differentfromtheendotoxin)actingoncellsurfaceBybindingtocertainreceptorsPossesssomedegreeofhostcellspecificitydenaturedbyformaldehydetreatmenttogeneratetoxoidswhichlacktoxicactivitybutstillinduceprotectiveimmunitywhenusedasvaccines.ManyexotoxinshaveanA-BsubunitstructureAsubunit--providesthetoxicactivityBsubunit--mediatesadherenceofthetoxincomplextoahostcell

SummaryExotoxinsToxinsproducedbybEndotoxins(LPS)

derivedfromG―cellwallsandareoftenliberatedwhenthebacterialyse.heat-stable,threemainregions

atoxiclipidA

acorepolysaccharide

Oantigenpolysaccharidesidechains

ThepathophysiologiceffectsofLPSaresimilarEndotoxins(LPS)derivedfroⅡ.PathwayofBacterialEntranceContact:directorindirect(Sexualcontact)Inhalation:transmittedbytherespiratoryroute(Airbornedroplets)Ingestion:ingestedandtransmittedthroughintestinaltracttotheoutsideandgetnewinfectionsbycontaminatingoffoodandwater,whichiscalledfecal-oralspread(Food,Water)Inoculation&bloodtransfusionAnimalvectors:transmittedbyanimalvectors(insectbitting)Ⅱ.PathwayofBacterialEntranResponsetoInfectioninfectionxdiseaseInnateimmunitynodiseaserecoveryadaptiveimmunityre-infectionnodiseasexResponsetoInfectioninfectionImmunityofextracellularbacterialinfection:antibodies(IgG,IgM,SIgA);phagocytes(neutrophils);complement;humoralimmunitymainly.Immunityofintracellularbacterialinfection:cell-mediatedimmunity(delayed-typehypersensitivity,DTHresponse(DTH)involvingTH1andmacrophages)mainly.

ImmunityofextracellularbactNodiseaseHostdefenseBacterialinfectionBalancebetweenInfectionandImmunity(immunity)NodiseaseHostdefenseBacteriaDiseasedevelopsonlyintherighthostandundertherightconditionsDiseaseHostPathogenEnvironmentDiseasedevelopsonlyintherDiseaseHostdefenseBacterialinfectionEnvironmentalconditionscanhelptiltthebalance

Environmentalsignalsoftencontroltheexpressionofthevirulencegenes.Commonsignals,include:Temperrature/Ironavailability:Cdiphtheriae/lowion/Osmolality/Growthphase/pH/SpecificionsDiseaseHostdefenseBacterialiSourcesofInfectionB.EndogenousInfection:opportunisticpathogeninfections

ExogenousInfectionPatientsCarriersAnimalsSourcesofInfectionB.EndogenTypesofBacterialInfectionAccordingtoinfectiousstate:Inapparentinfection:

withoutclearclinicsymptoms.ApparentInfection:

haveevidentclinicsymptoms.Accordingtoinfectioussites(LocalinfectionandGeneralizedorsystemicinfectionBacteriemia:bacteriacirculatebutnotmultiplyintheblood.Septicemia:Bacteriacirculateandmultiplyintheblood.Pyemia:producesepticemiawithmultipleabscessesininternalorgans.Toxemia:Bacteiamultiplyatinvadinglocationanddonotenterbloodstream,buttheexotoxinsenterbloodandcausecorrespondingtoxicsymptomsEndotoxemia:multiplyatlocationorinbloodstream,releasealotofamountendotoxinreleasedfrombacterialcellrupture

Carrier:

TypesofBacterialInfectionAcPrinciplesofDiagnosisandPreventionofBacterialInfectionPrinciplesofDiagnosisandPrManifestationsofInfection:

Signsandsymptomsvaryaccordingtothesiteandseverityofinfection.Diagnosisrequiresacompositeofinformation,includinghistory,physicalexamination,radiographicfindings,andlaboratorydata.

MicrobialCausesofInfection:

Infectionsmaybecausedbybacteria,viruses,fungi,andparasites.Thepathogenmaybeexogenous(acquiredfromenvironmentaloranimalsourcesorfromotherpersons)orendogenous(fromthenormalflora).

ManifestationsofInfection:SThequantitymaterialmustbeadequate.Collectfromappropriatesite.Preparesitetominimizecontamination.Wheneverpossible,collectspecimenspriortoantibiotics.Transportsystemmaximizedforpathogensurvivalshouldbeused.GeneralguidelinesforspecimencollectionThequantitymaterialmustbeBodyfluidforspecimencollectionBlood–septicemiaCerebrospinalfluid–bacterialmeningitisPeritoneal(abdominal)Pleural(chest)Synovial(joint)Pericardial(heart)UrineBodyfluidforspecimencollecSamplecollectiondevicesSamplecollectiondevicesMicroscopyandStains:cellularmorphologyandstainmaypermitpreliminaryidentification.Separation&Cultureofbacteria:Isolationofinfectiousagentsfrequentlyrequiresspecializedmedia.Nonselective(noninhibitory)mediapermitthegrowthofmanymicroorganisms.Selectivemediacontaininhibitorysubstancesthatpermittheisolationofspecifictypesofmicroorganisms.ColonymorphologycansometimesbeusefulinbacterialidentificationIdentificationofbacteria:Culturalcharacteristics:Growthcharacteristicsundervariousconditions,Biochemicalcharacterization:utilizationofcarbohydratesandothersubstrates,enzymaticactivitySerologyIdentification

AhighorrisingtiterofspecificIgGantibodiesorthepresenceofspecificIgMantibodiesmaysuggestorconfirmadiagnosis.GenomicMethodsAntimicrobialSusceptibility:Microorganisms,particularlybacteria,aretestedinvitrotodeterminewhethertheyaresusceptibletoantimicrobialagents.MicrobiologicExaminationMicroscopyandStains:cellulaMicroscopyandStains

Directexaminationofstainedorunstainedpreparationsbylight(brightfield)microscopyisarelativelysimple:

witha100oilimmersionobjective,a5to10eyepiece,optimallighting.

Thetwomostimportantmethods,theGramandacid-fasttechniques,

toclassifyaswellasstaintheorganism.employstaining,decolorization,counterstainingMicroscopyandStainsDirecteExamplesofGramStainsGramPositiveRodsandCocciGramNegativeRodsandCocciExamplesofGramStainsGramPoExamplesofAcid-FastStainsFullyAcid-FastRods(Mycobacteriumspecies)PartiallyAcid-FastRods(Nocardiaspecies)ExamplesofAcid-FastStainsFutypesofmediaforroutineculture:Thestandardmediumforspecimens:bloodagar,

----Usuallymadewith5%sheepblood.-----MostaerobicandfacultativelyanaerobicorganismswillgrowonbloodagarAsecondnecessarymedium:Chocolateagar,---amediumcontainingheatedbloodwithorwithoutsupplements,----Someorganismsthatdonotgrowonbloodagar,includingpathogenicneisseriaandhaemophilus,willgrowonchocolateagar.CulturetypesofmediaforroutineculSelectivemediaSelectivemediaisonethatgrowsonlycertainmicroorganismswhileinhibiting(orpreventing)othersfromgrowing,thatistosay,themediahascertainchemicalsthatallowoneorganismtogrowbutanotherorganismcannotgrowwiththoseingredientsinthemedia,thus,isselectivefortheorganismsthatcangrowinthatmedia.Therefore,mostcommonlygrowsonlyonetypeoforganism.SelectivemediaSelectivemediaDifferentialmediaDifferentialmediaisonethatdistinguishesonemicroorganismfromanother,itcangrowmorethanonemicroorganism,butdependingonhoweachorganismreactstothemedia(liketurnsred)itdifferentiatesfromanothermicroorganism.Inthistypeofmediaifyouaretryingtodistinguishbetween2typesofmicroorganisms,bothshouldgrowbuttheywillhavedifferentreactionstothemedia,andthrutheirvisiblereactionsyoucantellthemapart(differentiatethem).DifferentialmediaDifferentialGrowthonselective-differentialmedia,suchasSalmonella-Shigella(SS)medium,

eosin-methylene-blue(EMB)andMacConkeyagarTheselecteffectofthemediainsuppressingunwantedgram-positiveorganismsisexertedbybilesaltsorbacteriostaticdyesintheagar.Thedifferentialabilityofthesemediaisbasedonlactosefermentation:normalflorapositive(coloredcolonies)andpathogensnegative(colorlesscolonies).Growthonselective-differentiSeparationofbacteria:platestreaking.Bacteriologicplatestreaking.Separationofbacteria:plate細(xì)菌的感染診斷防治消毒滅菌Colony:thevisiblegrowthofbacteriaonsolidgrowthmedia.Ideally,thecolonyistheprogenyofone,oratmost,afewbacteria.Acolonywillusuallycontainmillionsofbacterialcells.Colonymorphologycansometimesbeusefulinbacterialidentification.Coloniesaredescribedastosuchpropertiesassize,shape,texture,elevation,pigmentation,effectongrowthmedium.ColonyColony:thevisiblegrowthof細(xì)菌的感染診斷防治消毒滅菌細(xì)菌的感染診斷防治消毒滅菌Growthonbloodagartotestforhemolyticpropertiesα-hemolytic:incompletelysisofredbloodcells,resultinginagreenishhaloaroundthecolonyβ-hemolytic:completelysisofredbloodcells,resultinginaclearhaloaroundthecolony-hemolytic:non-hemolytic1.Culturalcharacteristics:uniquenutritionalrequirements,pigmentproduction,hemolyticproperties

IdentificationofBacteriaGrowthonbloodagartotestfa(alpha)partialhemolysisgreenishcolor(i.e.S.pneumoniae)b(beta)completeclearingGroupAandBg(gamma)nolysisEnterococcus(groupD)hemolysisreaction-sheepbloodagara(alpha)hemolysisreaction-MacConkey’sAgarContainslactoseandapHindicator,E.colifermentlactosetoproduceacid,whichturnsthepHdyered.So,E.colicoloniesappearred.2.BiochemicalcharacterizationIdentificationofBacteriatheabilitytoattackvarioussubstratesortoproduceparticularmetabolicproductsMacConkey’sAgar2.Biochemical2.BiochemicalcharacterizationTripleSugarIronAgarIdentificationofBacteria2.Biochemicalcharacterizatio細(xì)菌的感染診斷防治消毒滅菌Asimpleapproachtorapiddiagnosis(asanexampleofantigendetection)isusedinmanydoctor'sofficesforthegroupAstreptococcus.Thepatient'sthroatisswabbedandstreptococcalantigenextracteddirectlyfromtheswab(withoutpriorbacteriologicalculture).Thebacterialantigenisdetectedbyaggregation(agglutination)ofantibodycoatedlatexbeads.Serologicidentificationofanantibodyresponse(inpatient'sserum)totheinfectingagentcanonlybesuccessfulseveralweeksafteraninfectionhasoccurred.

3.SerologyIdentificationuseofantibodiesofknownspecificitytodetectantigenspresentonwholebacteriaorfreeinbacterialextracts

IdentificationofBacteriaAsimpleapproachtorapiddiaSerologicalmethods–usedtodetectbothantigenandantibodyinspecimensThefastestandmostspecificwayImmunofluorescence–microscopy,FACSEnzyme-immunoassay–ELISA,WesternblotRadioimmunoassay–quantitateantigen-antibodycomplexSerologicalmethods–usedtoFACS(fluorescenceactivatedcellsorter)FACS(fluorescenceactivatedc4.GenomicMethods16SDNAsequencingLabeledprobesspecificforthe16SrRNAofaspeciesareadded,andtheamountoflabelonthedouble-strandedhybridismeasured.Thistechniqueiswidelyusedfortherapididentificationofmanyorganisms.Fluorescenceinsituhybridization(FISH)PolymeraseChainReaction(PCR)NucleicAcidSequenceAnalysisCheckerboardDNAhybridization(DNAmicroarray)IdentificationofBacteria4.GenomicMethods16SDNAsequELISA(Enzyme-LinkedImmunosorbentAssay)

ELISA(Enzyme-LinkedImmunosorE.coli16SRNAThe16SrRNAofeachspeciesofbacteriahasstable(conserved)portionsofthesequence.Manycopiesarepresentineachorganism.E.coli16SRNAThe16SrRNAoFISHFISHPCR(polymerasechainreaction)PCR(polymerasechainreactionBacteriamRNAcDNADNAmicroarraysBacteriamRNAcDNADNAmicroarray37oC–cDNAlabeledw/fluoresceintag25oC–cDNAlabeledw/rhodaminetagDNAarray~6000genes“Transcriptome”37oC–cDNAlabeled25oC–cDNA細(xì)菌的感染診斷防治消毒滅菌SummaryDirectmicroscopyFastGivesomehintsonthetypeofbacteriaLowsensitivityCultureHighsensitivityCanmakedefinitiveIDSlowOnlyworksonculturablebacteriaSerologicalassayFastHighspecificityCandetectbothantigenandantibodyEasy(canbeusedatchairsideorbedside)LowsensitivityGenomicbasedassayFastHighsensitivityandspecificityWorksonbothculturableandnon-culturablebacteriaEspeciallyusefulfordetectingslowgrowingbacteriasuchasT.b.RequirestechnicalexpertiseFalsepositiveornegativeSummaryDirectmicroscopyPreventionofBacterialInfectionPreventionofBacterialInfectArtificialactiveimmunityVaccinesareantigenspreparedfrompathogensthatcanraiseaprotectiveimmuneresponse,yetdonotcauseillness.ThesepreparedantigenswillstimulatebothBcellsandTcellsandhelptocreatememorycellsthatcanlatermountavigorousimmuneresponsetoanencounterwiththerealpathogen.ArtificialactiveimmunityVaccToxoids:amodifiedformofthetoxinthatpreservesitsantigenicitybuthaslostitstoxicity.Thishasbeenspectacularlysuccessfulwithtetanusanddiphtheria.Inactivatedvaccines:

Attenuatedlivevaccines:Specialvaccines:polysaccharidevaccine,subunitvaccine,(conjugatevaccine,bio-engineeredvaccine,chemicalvaccine,syntheticvaccine),nucleicacidvaccine,idiotypevaccine,autovaccine,etc.ArtificialactiveimmunityToxoids:amodifiedformofthArtificialpassiveimmunity

Antitoxin:e.g.Tetanusantitoxinanddiphtheriaantitoxin.Itisraisedinthehorse.Itismostimportanttogiveanintentedrecipientofequineserumapriortestdosetoexcludehypersensitivitysubjectswhomayhavebeensensitizedbyapreviousdoseofequineserum.Pooledimmunoglobulin:Itcontainsthenormalrepertoireofantibodiesforanadult,andcanprotectagainsthepatitisA,andmeasles.Specificimmunoglobulin:Preparationsofspecificimmunoglobulinareavailableforpassiveimmunizationagainsttetanus,hepatitisB,rabies,varicella-zoster.CytokineArtificialpassiveimmunityAnSterilization

andDisinfectionA.SterilizationAphysicalorchemicalprocessthatcompletelydestroysorremovesallmicrobiallife,includingspores.B.Disinfection

treatmenttodestroyharmfulmicroorganisms.C.Preservation

Thepreventionofmultiplicationofmicroorganismsinformulatedproducts,includingpharmaceuticalsandfoods.SterilizationandDisinfectionSterilization

andDisinfection

BactericidalAspecifictermreferringtothepropertybywhichabiocideisabletokillbacteria.Bactericidalactiondiffersfrombacteriostasisonlyinbeingirreversible;ie,the“killed”organismcannolongerreproduce,evenafterbeingremovedfromcontactwiththeagent.

BacteriostaticAspecifictermreferringtothepropertybywhichabiocideisabletoinhibitbacterialmultiplication;multiplicationresumesuponremovaloftheagent.SterilizationandDisinfectionDisinfectionPhysicalMethodsHeatRadiationFiltrationUltrasonicandSonicFreezingDisinfectionPhysicalMethodsSterilization

andDisinfectionⅠ.HeatHeatenergycanbeappliedinthreeways,intheformsofMoistheat(eitherboilingorautoclaving)DryheatPasteurization

SterilizationandDisinfectionMoistHeat:farmorerapidandeffectiveinsterilizationthandryheat,Atemperatureof100°Cwillkillallbutsporeformsofbacteriawithin2–3minutesinlaboratory-scalecultures;121°Cfor15minutesisutilizedtokillspores.Autoclavesorpressurecookersareusedforthispurpose.Autoclavesareusuallyoperatedat121°C,whichisachievedwithapressureof15lb/sq

Itsuse

：anymaterialsthatarenotdamagedbyheatandmoisture,heat-stableliquidsswabs,mostinstruments,culturemedia,rubbergloves.Ⅰ.HeatMoistHeat:farmorerapidanDryHeat:required:2hoursat180℃Itsuse:

sterilizationofglassware,incinerationofdisposableobjectspassageofbacteriologicneedles,coverslips,orsmallinstrumentsthroughthenameofaBunsenburner.

Themostwidelyusedtypeofdryheat:isthehot-airovenⅠ.HeatDryHeat:Ⅰ.HeatⅠ.Heat

Pasteurization,

whichisusedprimarilyformilk,consistsofheatingthemilkto62℃for30minutesfollowedbyrapidcooling.(“Flash”pasteurizationat72℃for15secondsisoftenused).Thisissufficienttokillthevegetativecellsofthemilk-bornepathogens,eg,Mbovis,Salmonella,Streptococcus,Listeria,andBrucella,butnottosterilizethemilk.Usedforfoods(milk,fruitDrinks,wine)andfragilemedicalequipment,tokillallvegetativebacteriaofsignificanceinhumandisease，butnotspores.Ⅰ.HeatPasteurization,whichⅡ.RadiationThetwotypesofradiationusedtokillmicroorganismsareUltraviolet(UV)light:Themosteffectivebactericidalwavelengthisinthe240to280nmrange,withtheoptimumatabout260nm,IonizingRadiations:havehigherenergyandpenetratingpowerthanUVradiationⅡ.RadiationThetwotypesofrUltravioletRadiation(UV)

Mechanism:UVlightcausesdirectdamagetoDNA,formationofthepyrimidinedimers,Asaresult,DNAreplicationisinhibitedandtheorganismscannotgrow.UseofUVlightinmedicineislimited

itspoorabilitytopenetrate

safety,becauseUVradiationcandamagethecorneaandskin,So,Itmustberememberedthatworkersexposedtoitmustbeappropriatelyprotected.itsmainapplication:

airofhospitalsiteslaboratoryfacilities

Ⅱ.RadiationUltravioletRadiation(UV)MeIonizingradiation

Mechanism:

carriesfargreaterenergythanUVlight.It,too,causesdirectdamagetoDNAandproducestoxicfreeradicalsandhydrogenperoxidefromwaterwithinthemicrobialcells.

widelyusedinindustrialprocesses,including

sterilizationof

manydisposablesurgicalsuppliessuchasgloves,plasticsyringes,specimencontainers,somefoodstuffs,Ⅱ.RadiationIonizingradiationMechanism:Ⅲ.FiltrationThemostcommonlyusedfilteriscomposednitrocelluloseandhasaporesizeof0.22m.Thissizewillretainallbacteriaandspores.Filtrationisthepreferredmethodofsterilizingcertainsolutions,especiallythosecontainingheat-labilecomponentssuchasserum,plasma,ortrypsin.Ⅲ.FiltrationThemostcommonlyⅳ.UltrasonicandSonicVibrations

Microorganismsvarymarkedlyintheirsensitivitytosonicandultrasonicvibrations.(Themostsusceptiblearethegram-negativerods,andamongthemostresistantarethestaphylococci.)

Althoughsonicvibrationsarelethaltomanymembersoftheexposedbacterialpopulation,therearenumeroussurvivors.

treatmentwithsonicvibrationisofnopracticalvalueinsterilizationanddisinfection.ⅳ.UltrasonicandSonicVibratⅤ.Freezing

Althoughmanybacteriaarekilledbyexposuretocold,freezingisnotareliablemethodofsterilization.Thismethodiswidelyusedforthepreservationofbacterialcultures.Ⅴ.FreezingAlthoughmanybactChemicalMethods:Chemicalagentsactprimarilybyoneof

threemechanismsDisruptionofthelipid-containingcellmembraneModificationofproteinModificationofDNAChemicalMethods:ChemicalageDisruptionofthelipid-containingcellmembraneAlcohols:

Itactsmainlybydisorganizingthelipidstructureinmembranes,butitdenaturesproteinsaswell.Cationicdetergents,particularlythequaternaryammoniumcompounds(“quats”)suchasbenzalkoniumchloride,theirhydrophobicandlipophilicgroupsreactwiththelipidofthecellmembraneofthebacteria,alterthemembrane’ssurfacepropertiesanditspermeability,andleadtolossofessentialcellcomponentsanddeath.Phenols:notonlydamagemembranesbutalsodenatureprotein.Itisoneofthefirsteffectivedisinfectants,usedintheoperatingroom(byListerin1860s),butitisrarelyusedasadisinfectanttodaybecauseitistoocaustic.Disruptionofthelipid-contai1.Chlorine:apowerfuloxidizingagentthatkillsbycrossing-linkingessentialsulfhydrylgroupsinenzymestoformtheinactivedisulfide.Chlorineisusedasadisinfectanttopurifythewatersupplyandtotreatswimmingpools.Itisalsotheactivecomponentofhypochlorite(bleach),whichisusedasadisinfectantinthehomeandinhospitals2.Iodine:

likechlorine,isanoxidantthatinactivatessulfhydryl-containingenzymes.Italsobindsspecificallytotyrosineresiduesinproteins.Iodineisthemosteffectiveskinantisepticusedinmedicalpractice.Itissuppliedintwoforms:Tinctureofiodine(2%solutionofiodineandpotassiumiodideinethanol)isusedtopreparetheskinpriortobloodculture.Becausetinctureofiodinecanbeirritatingtotheskin,itshouldberemovedwithalcohol.Iodophorsarecomplexesofiodinewithdetergentsthatarefrequentlyusedtopreparetheskinpriortosurgerybecausetheyarelessirritatingthantinctureofiodine.Modificationofprotein1.Chlorine:Modificationofpr3.HeavyMetals:Mercuryandsilverhavethegreatestantibacterialactivityoftheheavymetalsandarethemostwidelyusedinmedicine.Theyactbybindingtosulfhydrylgroups,therebyblockingenzymaticactivity.Thimerosal(Merthiolate)andmerbromin(Mercurochrome),whichcontainmercury,areusedasskinantiseptics.Silvernitratedropsareusefulinpreventinggonococcalophthalmianeonatorum.Silversulfadiazineisusedtopreventinfectionofburnwounds.Modificationofprotein3.HeavyMetals:Mercuryands4.HydrogenPeroxide:Hydrogenperoxideisanoxidizingagentthatattackssulfhydrylgroups,therebyinhibitingenzymaticactivity.italsoattacksmembranelipidsandothercellcomponents.Althoughitactsrapidlyagainstmanybacteriaandviruses,itkillsbacteriathatproducecatalase(anenzymethatdegradesH2O2)andsporeslessrapid