Note: Evaluation of selective media for the enumeration of Bifidobacteriumsp. in milk

Pure cultures of three species of bifidobacteria (Bifidobacterium longum, B if. adolescentis and Bif bifidum), Lactobacillus acidophilus and a mixed cu lture of Lact. delbrueckii subsp. bulgaricus and Streptococcus salivarius s ubsp. thermophilus were each enumerated on two differential media and six s elective media for the enumeration of bifidobacteria. The appearance of the colonies on the differential media was as expected but when mixed cultures were present, it proved extremely difficult to distinguish one species fro m another. Of the selective media, AMC, RMS, NPNL and BL-OG performed well in that they gave good recoveries of bifidobacteria and were inhibitory to the growth of Lact. delbrueckii subsp. bulgaricus, Strep. salivarius subsp. thermophilus and Lact. acidophilus. However, of these four media, AMC was most convenient as it is based on a commercially available medium, whereas the others must be made up from individual constituents. The AMC agar is th us a good choice for the routine enumeration of bifidobacteria from mixed c ultures.