Use of M17 and a milk-based medium enables isolation of two distinct and diverse populations of Lactococcus lactis strains from undefined mesophilic starter cultures

Dairy starter culture development and bacteriophage research depends on adequate growth media for isolation of relevant starter culture strains and their bacteriophages. We show that the use of two growth media, M17 and a milk-based medium (GMA), enables isolation of two distinct subpopulations of Lactococcus lactis ssp. from undefined mesophilic starter cultures. Phage typing revealed large diversity within each subpopulation, and interestingly, that there was very little overlap in phage sensitivity between the two sets of bacteria. Acidification activity tests performed in the presence of M17-and GMA-derived bacteriophages, both separately and in combination, demonstrated the relevance of both bacterial subpopulations in the acidification process. Use of both media enables higher diversity sampling of Lactococcus ssp., and their bacteriophages.