EVALUATION OF MEDIA FOR SELECTIVE ENUMERATION OF LACTOBACILLUS-ACIDOPHILUS AND BIFIDOBACTERIUM SPECIES

Seven different media were evaluated to determine their suitability fo r selective enumeration of Lactobacillus acidophilus and Bifidobacteri um spp using six strains of Streptococcus salivarius ssp thermophilus, five strains of Lactobacillus delbrueckii ssp bulgaricus, six strains of Lactobacillus acidophilus and nine strains of Bifidobacterium spp. The media which were evaluated were NNLP agar, Bile agar, MRS-galacto se agar, MRS-maltose agar, MRS-dextrose agar, MRS-L-arabinose agar and RCA agar. NNLP agar was found to be suitable for selective enumeratio n of B. bifidum, B. longum, B. pseudolongum and B. thermophilum as thi s medium suppressed the growth of S. salivarius thermophilus, L. delbr ueckii ssp bulgaricus and of L. acidophilus. Bile agar can be used for selective enumeration of L. acidophilus from a product containing L. acidophilus and B. bifidum, B. adolescentis, B. breve or B. longum 200 97. Other strains of bifidobacteria grew in Bile agar. MRS-maltose aga r can be used for selective enumeration of L. acidophilus from yogurt organisms in a product which does not contain Bifidobacterium spp. MRS -L arabinose agar suppressed the growth of S. salivarius ssp thermophi lus, L. delbrueckii ssp bulgaricus, L. acidophilus and bifidobacteria except that of B. longum and B. pseudolongum. Thus, this medium can be used for selective enumeration of B. longum and B. pseudolongum only. In a separate experiment, MRS-L-arabinose agar and NNLP agar were use d to selectively enumerate B. longum 1941 from yogurt prepared with S. salivarius ssp thermophilus, L. delbrueckii ssp bulgaricus, L. acidop hilus and B. longum 1941 as starter cultures. B. longum colonies were easily differentiated from that of L. acidophilus, which formed tiny c olonies, while S. salivarius ssp thermophilus and L. delbrueckii ssp b ulgaricus did not form any colonies.