Characterization of lactococci isolated from homemade kefir

Abstract

Five bacteriocin-producing lactococci isolates from traditionally prepared kefir were determined as Lactococcus lactis subsp. lactis. The analyzed isolates showed different plasmid profiles and no cross inhibition between them was detected. Moreover, natural isolate BGKF26 was resistant to the antimicrobial activity of nisin producing strain NP45. Plasmid curing experiments revealed that the genes encoding bacteriocin and proteinase production are located on separate genetic elements, except in BGKF26. Production of the tested bacteriocins depends on the concentration of casitone or triptone in the medium. Higher concentrations of casitone or triptone induce bacteriocin activity. Our DNA-DNA hybridization analyses suggest that the analyzed antimicrobial compounds probably are lactococcin-like bacteriocins.Pet izolata laktokoka proizvodjaca bakteriocina izolovanih iz kefira pripremljenog na tradicionalan nacin determinisano je kao Lactococcus lactis subsp. lactis. Analizirani izolati poseduju razlicite plazmidne profile i medju njima nije detektovana uzajamna antimikrobna aktivnost. Takodje prirodni izolat BGKF26 je rezistentan na aktivnost soja NP45, proizvodjaca nizina. Eksperimenti ciscenja plazmida pokazali su da se geni _a sintezu bakteriocina i proteinaza nalaze na razlicitim genetickim elementima, osim kod izolata BGKF26. Sinteza analiziranih bakteriocina zavisi od koncentracije kazitona ili triptona u medijumu. Vise koncentracije kazitona ili triptona indukuju bakteriocinsku aktivnost. Hibridizacioni eksperimenti su pokazali da su analizirani bakteriocini najverovatnije slicni laktokokcinima.