12英文文章大肠杆菌感染.docx

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.

At7dofage,durin