We have exposed three different bacterial strains Escherichia coli Leclercia adecarboxylata and Staphylococcus aureus to the magnetic field 30 min 10mT 50 Hz in order to compare their viability number of colonyforming units CFU We have measured t ID: 24310
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Comparisonofthelow-frequencymagneticfieldeffectsonbacteriaEscherichiacoliLeclerciaadecarboxylataStaphylococcusaureus,LudekStras,VladimrVetterl,JanSInstituteofBiophysics,AcademyofSciencesoftheCzechRepublic,Kralovopolska *Correspondingauthor.InstituteofBiophysics,AcademyofSciencesoftheCzechRepublic,Kralovopolska135,Brno61265,CzechRepublic.Tel.:+420-5-41-51-71-43;fax:+420-5-41-21-12-93.E-mailaddress:vetterl@ibp.cz(V.Vetterl).www.elsevier.com/locate/bioelechemBioelectrochemistry63(2004)337341 Thetemperatureinsidethecoilwasmaintainedatthevalueofthelaboratorytemperature(2025C)byairflowanditwasmeasuredbythermometer.Thesampleswereplacedonthenonconductivestandinthecentreofthecoil.BacteriawereexposedinPetridishes(diameterof80mm).ThebacteriaE.coli(strainK12,Row,genotype58161metB1rpsLP.Fredericq),L.adecarboxylata2177)andS.aureus(FA812)wereused.TYbroth(8gtryptone,5gyeastextractHiMediaLab.,Bombay;5gNaClLachemaBrno/1lwater)andbasicnutrientagar(40g/lImunaSMichalany)wereusedforcultivationofthebacteria.Thenumberofcolony-formingunits(CFU)wasusedtoquantifyourresults.Freshbacterialcultureswereusedthroughouttheexperiments.Intheexperimentsatwhichexposuretimesormagneticinductionswerevaried,appropriatelydilutedbacterialcul-tureswereexposedtothemagneticfieldsonagarplatesinthephaseoftheirlogarithmicgrowth(4.5hsinceinocula-tion).Forstudiesofthedynamicsofgrowth,brothcultureswereexposedtothemagneticfieldsinthelogarithmicgrowthphaseatdifferenttimeintervals,andthenthesamplesweretransferredtoagarplatesforCFUcounts.Forstatisticalanalysisoftheresults,theStudentsstatis-ticsatthe0.95levelofsignificancewasused.3.Resultsanddiscussion3.1.DependenceofCFUonthetimeofexposureWeexposedthebacterialcellsontheagarplatestothea.c.magneticfields(=50Hz,=10mT).WehavefoundthatthenumberofCFUdecreaseswiththetimeofexposureforallbacterialsamples(Fig.2).Thedecreaseisexponential.ItcanbeseenthatthemostsensitivestraintothemagneticfieldisE.coli,theleastsensitiveisS.aureus.3.2.DependenceofCFUonthemagnitudeofmagneticinductionBacteriawereexposedtothemagneticfieldsfor12min.Theamplitudeofmagneticfieldinductionvariedbetween2.7and10mT.TheresultsshowedanexponentialdecreaseofCFU,thebiggestdecreasewasobservedforE.coli Table1Diameter235mmInnerdiameter205mmLength210mmWeight5.7kgNumberofthreads880Diameterofwires2mm Fig.1.Dependenceofthemagneticfieldinductioninthecoilonthedistancefromthecoilaxisfordifferentcurrentvalues:1.9A,1.5A,0.5A(theverticallineinthegraphatthedistance110mmrepresentstheradiusofthecoil).L.Fojtetal./Bioelectrochemistry63(2004)337341 .Asitwasstatedabove,thestrainmostsensitiveforthemagneticfieldseffectsisE.coli3.3.ThestudyofgrowthdynamicsThenumberofCFUwascountedduringtheexposureoftheculturesandcomparedwiththecontrolone.Magneticfieldwasturnedoff60minafterthebeginningoftheexposure.Afterexposurewecontinuedwiththemeasure-mentofthetimedependenceofCFUontime(biologicalageofculture).WeobservedthedecreaseofCFUinthesamplesexposed(Figs.4and5)4.DiscussionOurworkhascollectedtheresultsofmagneticfieldeffectsonthethreestrainsofbacteria. Fig.2.DependenceoftherelativenumberofCFUonthedurationoftheexposure(=10mT).E.coliL.adecarboxylataS.aureus Fig.3.DependenceoftherelativenumberofCFUonthevalueofthemagneticfieldinduction(=12min).E.coliadecarboxylataS.aureusL.Fojtetal./Bioelectrochemistry63(2004)337341 Wehaveusedwell-describedgram-negativeE.colirelativestrainL.adecarboxylataandatotallydifferent(gram-positive)strainS.aureus.WehavecomparedthechangesintheCFUnumbersafterthemagneticfieldexposureasafunctionofthedurationoftheexposureorthemagneticfieldinduction.Alldatawerecomparedwiththecontrolonesandthedependencies((0)==constand((0)==constweredeter-mined.Wehavefoundthatthetimedependenceand/ormagneticfieldinductiondependencecanbeapproximatedbyanexponentialfunction,respectivelyTheparameterscharacterisethemagneticfield Fig.4.DependenceofthenumberofCFUforE.coliduringandaftermagneticfieldexposure(magneticfieldwasswitchedoffat=60min).Theerrorbarsareat95%confidenceinterval(isnumberofbacteriain100lofsuspension).exposedsample(=10mT),controlsample. Fig.5.DependenceofthenumberofCFUforS.aureusduringandafterthemagneticfieldexposure(magneticfieldwasswitchedoffat=60min).Theerrorbarsareat95%confidenceinterval(isthenumberofbacteriain100lofsuspension).exposedsample(=10mT),controlsample.L.Fojtetal./Bioelectrochemistry63(2004)337341 effects.Theaccuracyoftheapproximationisgivenbyparametergivenbytheformula: Yi¯Yi2Y2i arethemeasuredrelativenumbersofCFU,valuesofarithmeticalaverage,isthenumberofdatameasured.ItcanbeseenthatthemagneticfieldcausesthedecreaseofCFUinallexposedsamples.WeknowthatmagneticfieldkillsthebacteriaE.colicoli.NowwecanconcludethatasimilareffectoccurswithL.adecarboxylataS.aureus(observationsfromFigs.2and3).Thisfactwassupportedbythe-test.Thedecreaseofnumberofbacteriawasinallcasessignificantatthe95%confidencelevel(datanotshown).Interestingly,thequalityofmathematicalmodelinFig.2ispoor(errorisabout50%).Buttheregressioninisverygood.Thismodelshowsusthatallthebacterialstrainsreacttothemagneticfieldinthesameway;onlythestrengthofthereactionisdifferent.Thequalityoftheeffectisthesameandthequantityoftheeffectisstrain-dependent.ThebiggestdecreaseofCFUwasobservedforE.coli,thestrainmostresistanttothemagneticfieldwasS.aureus.havecomparedtwobacterialstrains(E.coliS.aureusstudyingthegrowthdynamics.BothexposedcultureshavesmallerCFUnumbersthanthecontrolones.Thequestionofhowthemagneticfieldcankillbacteriawasnotsolvedbyourexperiments.Themaintheoriesthattrytoexplainthebiologicaleffectsofelectromagneticfieldsarebasedonthepossibleeffectsonthepermeabilityoftheionicchannelsinthemembranebrane.Thiscanaffectiontransportintothecellsandthiscanresultinbiologicalchangesintheorganisms.Theotherpossibleeffectsaretheformationoffreeradicalsduetomagneticfieldexposure.AcknowledgementsThisworkwassupportedbytheGrantAgencyoftheCzechRepublic,GrantNo.310/01/0816andbytheGrantAgencyoftheAcademyofSciencesoftheCzechRepublic,GrantNo.S5004107andNo.A4004404.References[1]M.Feychting,A.Ahlbom,MagneticfieldsandcancerinchildrenresidingnearSwedishhigh-voltagepowerlines,Am.J.Epidemiol.138(1993)467481.[2]N.Pearce,J.Reif,J.Fraser,Case-controlstudiesofcancerinNewZealandelectricalworkers,Int.J.Epidemiol.18(1989)5559.[3]M.R.Scarfi,M.B.Lioi,M.DellaNoce,O.Zeni,C.Franceschi,D.Monti,G.Castellani,F.Bersani,Exposureto100Hzpulsedmagneticfieldsincreasesmicronucleusfrequencyandcellprolif-erationinhumanlymphocytes,Bioelectrochem.Bioenerg.43(1997)7781.[4]L.Monti,M.S.Pernecco,R.Moruzzi,P.Battini,B.Zaniol,B.Bar-biroli,EffectofELFpulsedelectromagneticfieldonproteinkinaseCactivationprocessesinHL-60leukemiacells,J.Bioelectr.12(1991)119130.[5]J.Schimmelpfeng,H.Dertinger,Theactionof50HzmagneticandelectricfieldsuponcellproliferationandcyclicAMPcontentofculturedmammaliancells,Bioelectrochem.Bioenerg.30(1993)143150.[6]I.Ho¨nes,A.Pospichil,H.Berg,ElectrostimulationofproliferationofthedenitrifyingbacteriumPseudomonasstutzeri,Bioelectrochem.Bioenerg.44(1998)275277.[7]M.S.Davies,Effectsof60Hzelectromagneticfieldsonearlygrowthinthreeplantspeciesandareplicationofpreviousresults,Bioelec-tromagnetics17(1996)154161.[8]T.D.Xie,Y.D.Chen,P.Marszalek,T.Y.Tsong,Fluctuation-drivendirectionalflowinbiochemicalcycle:furtherstudyofelectricactivationofNa,Kpumps,Biophys.J.72(1997)24962502.[9]J.Galvanoskis,J.Sandblom,Periodicforcingofintracellularcalciumoscillators.Theoreticalstudiesoftheeffectsoflow-frequencyfieldsonthemagnitudeofoscillations,Bioelectrochem.Bioenerg.46(1998)161174.[10]J.L.Phillips,W.Haggren,W.J.Thomas,T.Ishida-Jones,W.R.Adey,Magneticfield-inducedchangesinspecificgenetranscription,Bio-chim.Biophys.Acta1132(1992)140144.[11]H.Berg,Problemsofweakelectromagneticfieldeffectsincellbiology,Bioelectrochem.Bioenerg.48(1999)355360.[12]R.S.Mittenzwey,W.Mei,Effectsofextremelylow-frequencyelec-tromagneticfieldsonbacteriathequestionofaco-stressingfactor,Bioelectrochem.Bioenerg.40(1996)2127.[13]M.P.Greenbaum,Anupperlimitfortheeffectof60HzmagneticfieldsonbioluminescencefromthephotobacteriumVibriofisherBiochem.Biophys.Res.Commun.18(1994)4044.[14]L.Strask,V.Vetterl,J.Smarda,Effectsoflow-frequencymagneticfieldsonthebacteriaEscherichiacoli,Bioelectrochem.Bioenerg.55(2002)161164. E.coliL.adecarboxylataS.aureus=10mT)0.0302min0.0121min0.0096min)0.610.480.64Numberofrepetitionofexperiments7611=12min)0.0469mT0.0347mT0.019mT)0.980.950.83Numberofrepetitionofexperiments6610L.Fojtetal./Bioelectrochemistry63(2004)337341