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InternationalDairyJournal9(1999)497}505 CulturemediafortheenumerationofBixdobacteriumbixdum andLactobacillusacidophilusinthepresenceofyoghurtbacteria C.G.Vinderola,J.A.Reinheimer* ProgramadeLactologn&aIndustrial,FacultaddeIngeniern&aQun&mica(UniversidadNacionaldelLitoral),SantiagodelEstero2829,3000SantaFe,Argentina Received8January1999;accepted14May1999 Abstract Aproposedmethodologyfortheenumerationofprobioticbacteria(bi"dobacteriaandLactobacillusacidophilus)inthepresenceof yoghurtbacteriaisdescribed.Commercialmixedculturesofyoghurt(fourcultures),L.acidophilus(twocultures)andBixdobacterium bixdum(twocultures)wereassayedusingatotalof15culturemediafromfouragarcategories:nonselective(SkimMilk(SM),MRS andM17);modi"ed(GalactoseMRS(G-MRS),GalactoseM17(G-M17)andTrehaloseMRS(T-MRS));di!erential(LacticBacteria Di!erential(LBD),Lactic-andL-S);andselective(NalidixicParomomycinNeomycinLithiumMRS(NPNL-MRS),Nalidixic NeomycinLithiumMRS(NNL-MRS),NalidixicKanamycinLithiumMRS(NKB-MRS),Bile-MRS,OxgallGentamicinMRS (OG-MRS)andLithiumPropionateMRS(LP-MRS)).Everycultureusedwastestedforitsgrowthoneachmediumunderthree di!erentincubationconditions(aerobic,anaerobicwithcombustionandanaerobicinGasPak)at373Cfor72h.SMandMRSagar weretakenasreferencemediaforyoghurtandprobioticbacteria,respectively.Foreachorganism,thecellrecoveryrateoneach mediumwascomparedstatisticallywiththatobtainedonthereferencemedia.Theabilityofeverymediumtodi!erentiateorinhibit theorganismswasalsotested.SMandLBDagar(aerobic)wereusefultoenumerateyoghurtbacteriaandinhibitbi"dobacteria. T-MRSandBile-MRSagar(aerobic)onlyallowedthegrowthofL.acidophiluscultures.ForBixdobacteriumbixdum,aselectivecount couldbeperformedonLP-MRSagar(anaerobic,GasPak).Thissetofmediawasdemonstratedtobee!ectivefortheenumerationof S.thermophilus,Lactobacillusdelbrueckiisubsp.bulgaricus,L.acidophilusandBixdobacteriumbixdumincommercialdairyprod- ucts.(1999ElsevierScienceLtd.Allrightsreserved. Keywords:Bixdobacteriumbixdum;Lactobacillusacidophilus;Yoghu