Growth of Lactobacillus dairy cultures on two different brands of MRS medium

The growth of 5 species of Lactobacillus was tested on 2 brands of MRS medi um. Lactobacillus delbrueckii subsp. bulgaricus strain 11842 (LB 11842) sho wed significantly (p <0.0001) better growth on Brand A compared to Brand B, the actual difference between the means of the viable count being approxim ately 5-fold. Higher counts were coupled with lower final pH of the spent m edium. With respect to ingredients, brand B contained a lower content of ye ast extract than Brand A, which could be partly responsible for the lower p opulations observed. Results indicate that lower counts on Brand B are not due to death of the organisms. L. acidophilus and C. plantarum strain 8014 also showed significantly higher (p <0.01, and p <0.03, respectively) growt h on Brand A. There was no significant difference in the growth of L. helve ticus strain 32K on the 2 media, while L. delbrueckii subsp. bulgaricus str ain 12 showed significantly better growth on medium B (p <0.005). After gro wth in skim milk, no differences were found in viable counts of the 5 organ isms when enumerated on either brand, although generally colonies were larg er on Brand A.