PresentationattheWorldVeterinaryPoultryAssociation,Cairo,Egypt,January2002p.200 Introduction: Mycoplasmainfectioncontinuestobeanimportantcauseoflossinpoultryproduction.Kleven(1990)describedthelossesduetoMycoplasmagallisepticum(MG).Thesewereareductionineggproductionof10-20%,anincreaseinembryomortalityandchickmortalityof5-10%andareductioninweightgainandfeedconversionefficiencyof10-20%.InspiteoftheavailABIlityofvaccines,antimicrobialusecontinuestobethemosteconomicmethod(Stipkovitsetal,1993)ofcontrollingtheseinfections,wherethediseasesarestillendemic. Asaresult,resistancehasdevelopedtoanumberofantimicrobialsandthepurposeofthispaperistoreviewtheactivityoftiamulinandseveralantimicrobialsagainstanumberofcommonpathogenicpoultrymycoplasma,MG,M.synoviae(MS),M.meleagridis(MM)andM.iowae(MI)andcomparetheirresistancedevelopmentoverthelast25years. MaterialsandMethods: Asearchofpublishedliteraturewascarriedoutandthesedatawascombinedwithourowninternalreports.Atotalof20referenceswerecompiled.Reportsfrom1975-1989andfrom1990-2000werecompared.Therangesofminimuminhibitoryconcentrations(MICs)ofvariousantimicrobialsagainstvariousmycoplasmaspecieswereenteredintoadatabase.Themaximumandminimumdataforeachtimeperiodwerecomparedfortiamulin,tylosin,oxytetracycline,lincomycinandenrofloxacin. Results: Fromthe20referencesandreports,13werefrombefore1990andsevenfrom1990andafter.Therewasinformationon241isolatesofMG,105ofMS,28ofMMand111ofMI.Thecomparativedataforthefourmycoplasmaspeciesaresummarizedinthetablesbelow. Table1.Mycoplasmagallisepticum,MICranges(µg/ml)bytimeperiod(no.ofisolates) Antimicrobial 1975-1989(175) 1990-2000(66) Tiamulin 0.0039-0.78 0.006-0.39 Tylosin 0.01-75 0.006-400 Oxytetracycline 0.12-10 0.05-200 Lincomycin 0.4-64 0.125-6.25 Enrofloxacin 0.01-0.25 0.0125-2.0 Table2.Mycoplasmasynoviae,MICranges(µg/ml)bytimeperiod(no.ofisolates) Antimicrobial 1975-1989(53) 1990-2000(52) Tiamulin 0.031-1.0 0.006-0.5 Tylosin 0.015-75 0.006-50 Oxytetracycline 0.06-0.08 0.025-100 Lincomycin 0.31-6.0 0.05-1.56 Enrofloxacin 0.1-1.0 0.025-1.56 Table3.Mycoplasmameleagridis,MICranges(µg/ml)bytimeperiod(no.ofisolates) Antimicrobial 1975-1989(17) 1990-2000(11) Tiamulin 0.03-1.0 0.025-3.13 Tylosin 0.015-3.0 0.78-50 Oxytetracycline 0.3-5.0 0.05-25 Lincomycin 0.5-5.0 0.05-25 Enrofloxacin 0.015-1.0 0.1-3.13 Table4.Mycoplasmaiowae,MICranges(µg/ml)bytimeperiod(no.ofisolates) Antimicrobial 1975-1989(25) 1990-2000(86) Tiamulin 0.015-10 0.006-0.125 Tylosin 0.05-64 0.05-100 Oxytetracycline 1-3 0.025-100 Lincomycin 3-64 0.05-100 Enrofloxacin 0.1-1.0 0.005-1.0 Conclusions: MGhasshownnoresistancedevelopmenttotiamulinoverthelast25yearsandall241isolatescouldbeconsideredsensitive.Incontrastthereisresistancedevelopmenttotylosin,oxytetracycline,lincomycinandborderlineresistancetoenrofloxacinandthisappearstohaveincreasedinthelastdecade. MShasshownnoincreaseinresistancetotiamulinandalmostallofthe105isolateswouldbeconsideredsensitive.Incontrast,resistancehasdevelopedtotylosinandoxytetracycline.Levelsofresistancetolincomycinremainlowandallstrainscouldbeconsideredsensitivetoenrofloxacin. MMisolates(28)fromturkeysshowsomeresistancetotiamulinandenrofloxacin.However,tylosin,oxytetracyclineandlincomycinshowamarkedincreaseinresistancedevelopment. MIhasdevelopedalmostnoresistancetotiamulinandenrofloxacin.Intheninetiesallisolateswouldbeconsideredsensitive.Highlevelsofresistancehavedevelopedtotylosin,oxytetracyclineandlincomycin. ThesefindingsconfirmthoseofDrewsandothers(1975)andStipkovitsandBurch(1993)thattiamulinisalowinducerofresistanceinmycoplasmaincomparisonwithtylosinandslowerthanoxytetracyclineandenrofloxacin(StipkovitsandBurch,1993)asresistancehasnotdevelopedwithlong-termuse.FurThermore,thehighestMICleveloftiamulinagainstMGinrecentyearsis16timeslowerthanthatoflincomycin. Inconclusion,tiamulincouldbeconsideredahighlyeffectivetherapeuticinmycoplasmacontrolprogramsforbothchickensandturkeys. 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