12英文文章大肠杆菌感染.docx
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12英文文章大肠杆菌感染.docx
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12英文文章大肠杆菌感染
β-glucanandE.coliinfection
Introduction
Escherichiacoliiscommonlyfoundintheaviangastrointestinaltractandothermucosalsurfaces.Althoughmostofthestrainsarecommensals,aseparategroup,designatedavianpathogenicE.coli,hastheabilitytocauseextraintestinaldiseaseinpoultry,collectivelycalledcolibacillosis(Kariyawasametal.,2006;Bonnetetal.,2009).SerotypesO1,O2,andO78,andtosomeextentO15andO55,arethemostcommonserotypesassociatedwithcolibacillosisfoundinchickens(Gomisetal.,1997;Rajietal.,2007).Theycommonlycauseairsacculitis,pericarditis,perihepatitis,peritonitis,salpingitis,andsubsequentlythemostacuteform,septicemia,resultinginsuddendeath(Mellataetal.,2003;Asketal.,2006).Thepoultryindustriesworldwidesuffergreatfinanciallosseseveryyearbecauseofthehighmorbidityandmortalityratescausedbycolibacillosis.Treatmentstrategiesincludethecontrolofenvironmentalfactorsandtheuseofantibiotics.However,concernsexistregardingtheemergenceofantibioticresistanceofnormalmicrofloraandpathogenicbacteria,whichmayinturnthreatenhumanhealththroughtransferfdrugresistancegenestozoonoticbacteria(FoodandgricultureOrganizationoftheUnitedNations,WorldealthOrganization,andWorldOrganizationforAnimalealth,2003).
Aviancolibacillosis,adiseasecausedbyagroupofbacteriacalledavianpathogenicEscherichiacoli(APEC)inchickens,turkeys,andotheravianspecies,isaninfectiousdiseasethatoftencausesseveremortalityandsubsequentlyresultsineconomiclossestothepoultryindustry(Gibbsetal.,2004).Thediseaseisassociatedwithacompletesetofsyndromesincludingsepticemia,airsaculitis,pericarditis,andswollenheadsyndrome(Cheville
andArp,1978;Rodriguez-Sieketal.,2005).SeveralE.coliisolatesarecommonlyassociatedwithcolibacillosis
inpoultry,andtheserogroupsO1,O2,andO78havebeenrecognizedasthepredominantsourcesinvolvedinthisdisease(WhittamandWilson,1988;McPeakeetal.,2005).AhighraAhighrateofantibioticresistancewasobservedwhiletestingtheseserogroups,whichprobablyoriginatesfromtheextensiveuseofantibioticsinthepoultryindustry(Allanetal.,1993),aswellasbyacquisitionofRplasmids(Johnsonetal.,2005b;Skybergetal.,2006).Numerousconcernsabouttheuseofantibioticsinthepoultryindustryhavebeenraisedincludingthefurtherselectionofdrug-resistantstrains(Franklin,1999;Anguloetal.,2004).TherearealsohumanhealthissuesinvolvedduetothepotentialtransferofE.colifromanimalsviathefoodchain(Anguloetal.,2004;Johnsonetal.,2005a).Thishasattractedconsiderableattentionfromresearcherswhoareseekingalternativesforcontrolandtreatmentofcolibacillosisinanimals.
OnepromisingalternativetoantibioticsistheuseofvirulentbacteriophageagainstE.coliserogroupsO1,O2,andO78,awell-establishedapproachthatphagesfortheseserogroupsareabletobeisolatedandusedinphagetherapyagainstbacterialcells.Bacteriophagesareaclassofvirusesthatliveandreplicateinbacteria(Ackermann,2000)andhavetheabilitytoattackasinglespeciesorsubsetofaspeciesofbacterium,makingthempotentialantibacterialagents.
β-Glucanshavebeenwellstudiedinhumanandanimalsubjects,andtheirimmune-enhancingeffectshavebeenwellnoted(Volmanetal.,2008).Duetotheirabilitytoaugmenttheimmuneresponse,β-glucanshavebeentermedbiologicalresponsemodifiers.
β-Glucansarestructuralcomponentsofthecellwallofmanybacteria,fungi,andyeast,aswellascerealgrainssuchasoatandbarley.β-Glucansfromfungalandyeastsourceshavebeenwidelystudiedandshowntobemosteffectiveinenhancingprotectiveimmunityagainstinfectiousagents(Soltanianetal.,2009).
Thoughtheimmune-enhancingcapabilitiesofβ-glucanshavebeenproveninmammals,limitedreportedresearchisavailableforpoultry,withmixedresultsintermsofperformanceandimmuneresponse.Somestudieshaveshownthatβ-glucansupplementationimprovesBW(Zhangetal.,2008),whereasothergroupshavefoundnosignificanteffects(Chaeetal.,2006).Huffetal.(2006)reportedcontradictoryresultsinwhichβ-glucansupplementationwasdetrimentaltoBWinanonchallengesettingbutwasfoundtobebeneficialduringanEscherichiacolichallenge.Thesevaryingresultsindicatethatmoreresearchneedstobecarriedouttodeterminetheoptimaldosageandproperusageofβ-glucanstoobtainconsistentresults.β-Glucanshavebeneficialeffectsonboththeinnateandadaptiveimmunesystems.Whenexposedtoβ-glucansinvitro,chickenmacrophagesandsplenocyteshavebeenshowntoexperienceenhancedproliferationandimprovedphagocyticcapabilities(Chenetal.,2003;Guoetal.,2003).Intermsoftheadaptiveimmuneresponse,β-glucansmagnifyplasmaIgGandIgAlevels,indicatinganupregulationofthehumoralimmuneresponse(Zhangetal.,2008).TheT-lymphocytesubpopulationsarealsoaffected,withhigherCD4+,CD8+,andCD4+:
CD8+T-cellpopulationsfoundinchickenssupplementedwithβ-glucan(Chenetal.,2003;Chaeetal.,2006).Furthermore,β-glucanshavedemonstratedtheabilitytoaugmentthesecretionofseveralcytokinestoaidinpathogenelimination.Macrophagesisolatedfrombirdsfedβ-glucansdemonstratedenhancedinterleukin(IL)-1(Guoetal.,2003),IL-2,andinterferon(IFN)-γlevels(Zhangetal.,2008).Dietaryβ-glucanhasalsobeenshowntoincreasethesizeoftheprimaryandsecondarylymphoidorgans,providingfurtherevidence
oftheirimmunomodulatingcapabilities(Guoetal.,2003;Zhangetal.,2008).
Materialsandmethods
ExperimentalAnimalsandTreatments
A3-wkexperimentwasconductedtodeterminetheefficacyofbacteriophageEC1intreatingrespiratoryinfectioninbirdscausedbyE.coliO78:
K80.Atotalof480one-day-oldmalebroilerchicks(Ross308)wereobtainedfromacommercialhatchery.Thechickswereassignedrandomlyto4treatmentgroups,eachwith4pensof30chicksperpen.Waterandbroilerfeed(antibioticfree)wereprovidedadlibitumthroughouttheexperimentalperiod.The4treatmentgroupsweregroupI(control),inwhichuntreated,unchallengedbirdswereadministered0.2mLofPBSonly(0.14MNaCl,0.0027MKCl,0.01MNa2HPO4,0.0018MKH2PO4;pH7.4);groupII(control),inwhichunchallengedbirdsweretreatedwith0.2mLofbacteriophageEC1(1011pfu/mL);groupIII,inwhichbirdswerechallengedwith0.2mLofa5-h-oldE.coliO78:
K80culture(growninLuria-Bertanibrothat37°Candshakenat180rpm)containing109cfuofbacterialcells/mL,followedby0.2mLofbacteriophageEC1(1011pfu/mL)at2hpostchallenge;andgroupIV,inwhichbirdswerechallengedwith0.2mLofa5-h-oldE.coliO78:
K80culturecontaining109cfuofbacteriacells/mLonly.Thetimepointatwhichtoinoculatethebacteriophage(2hpostchallenge)wasselectedbasedontheresultsofapreliminarytrialshowingthatE.coliO78:
K80hadcolonizedthelungsandthatthebacteriahadspreadtootherorgans,suchastheliverandheart,2hafterthebirdswerechallengedwiththepathogen(datanotshown).Allthematerialswereinoculateddirectlyinto
thetracheaofthe1-d-oldchicksbyusingafeedingneedleinafarmsetting
TheBWoflivebirdsweretakenweekly.Samplingwascarriedoutond0(beforeinoculationofE.coliorbacteriophageEC1),1,2,3,7,14,and21from3ofthepensofeachtreatmentgroup.Thelastpenwasusedfortheobservationofmortalityrate.Oneachsamplingday,6birdsfromeachgroup(2randomlyselectedfromeachofthe3samplingpens)wereweighedandkilledbyCO2inhalationforlaboratoryexamination.Birdsthatdiedonthesamplingdaywerealsodissectedandsubjectedtothesamelaboratoryexaminations.AllanimalmanagementandsamplingprocedurescompliedwiththeguidelinesoftheGuidefortheCareandUseofAgriculturalAnimalsinAgriculturalResearchandTeaching(FederationofAnimalScienceSocieties,1999).
AnimalsandHousingConditions
Atotalof144specificpathogen-free(SPF)chickens(Valo;Lohmann-Tierzucht,Cuxhaven,Germany)hatchedattheClinicforAvian,ReptileandFishMedicine,UniversityofVeterinaryMedicine,Vienna,Austria,wereusedinthestudy.Thechickensweredistributedrandomlyandkeptundercontrolledconditionsinsterilizedisolationunits(MontairAndersenB.V.HM1500,Sevenum,theNetherlands;size:
1.2m2)withtheairflowof30to32m3/h.Thetemperaturewasadjustedat33°Cduringthefirstweekoflifeandlateronreducedgradually(2°Cperweek)to20°Cbytheageof6wk.Lightperiodwaskeptat12hthroughoutthetrial.Feed
andwaterwereprovidedadlibitum
Inexperiments,birdswerekeptunderincandescentlightingonalightscheduleconsistingof23hlightand1hdark.TheywereprovidedadlibitumaccesstowaterandanunmedicatedstandardcornandsoybeanbroilerstarterdietthatmetorexceededtheNRCrecommendedallowances(NationalResearchCouncil,1994),andwhichcontained3,000kcalofME/kgand21.0%CP.Birdswerefedanunsupplementeddietorthesamedietsupplementedwithalowlevel(LL)of500g/tonne(1lb/ton)orahighlevel(HL)of1,000g/tonne(2lb/ton)ofastandardizedyeastextractfeedsupplement(Alphamune).Individualbirdweightsandfeedconsumptionbypenweredeterminedweekly.
Thetemperatureofthecontrolroomwasmaintainedaccordingtoestablishedstandardoperatingprocedures.Broodersweresetat32.3Cforthefirstweek,afterwhichroomtemperaturewasmaintainedat24.8C1.5andRHat632.3%fortheremainderofthestudyusinganautomatedairhandlingsystem.
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