Method for differentiated enumeration of mixed cultures of thermophilic lactic acid bacteria and bifidobacteria by using only one culture medium

Abstract

The dairy industry has recently prepared probiotic products containing, in addition to the specific yoghurt cultures, Lactobacillus acidophilus and bifidobacteria. Identification of the species and enumeration of the micro-organisms are easier for yoghurt cultures than for probiotic products containing Lactobacillus delbrueckii subsp. bulgaricus, Streptococcus thermophilus, bifidobacteria and Lactobacillus acidophilus. A new method has been developed using the commercially available HHD 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 of 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. © Inra/Elsevier, Paris.