METHOD FOR DIFFERENTIATED ENUMERATION OF MIXED CULTURES OF THERMOPHILIC LACTIC-ACID BACTERIA AND BIFIDOBACTERIA BY USING ONLY ONE CULTURE-MEDIUM

The dairy industry has recently prepared probiotic products containing , in addition to the specific yoghurt cultures, Lactobacillus acidophi lus and bifidobacteria. Identification of the species and enumeration of the micro-organisms are easier for yoghurt cultures than for probio tic products containing Lactobacillus delbrueckii subsp. bulgaricus, S treptococcus thermophilus, bifidobacteria and Lactobacillus acidophilu s. A new method has been developed using the commercially available HH D agar, which provides a morphological differentiation of colonies and a counting of single species on the same plate. Results obtained with HHD are very close to those obtained by the use of media specific for each strain (MRS, MRS at pH 5.4, MRS + dicloxacillin, M17). Instead o f using many selective culture media, only one culture medium was used with saving of material and performance rapidity allowing the method to be applied to the routine controls of the probiotic products. (C) I nra/Elsevier, Paris.