Development of a culture medium for the detection and enumeration of bifidobacteria in fermented milk products

An agar medium was developed for the detection and enumeration of bifidobacteria in fermented dairy products. Screening experiments were performed to examine the recovery rates of various bifidobacterial species and strains on 19 different bifidobacteria media for further methodological development. Subsequently, the elective properties of an MRS-based medium containing L-cysteine-HCl and sheep's blood serum were optimized. Several comparative tests showed that the growth of bifidobacteria in could be enhanced markedly by adding a mixture of water-soluble vitamins, lactulose syrup and human milk whey to the MRS-based medium. In another test series, the selective properties of the substrate were improved. Based on antibiotic inhibitory profiles and confirmatory trials in liquid media, supplementation of the medium with an antibiotic mixture consisting of Aztreonam (8 mg L(-1)), Nalidixic acid (6 mg L(-1)), Netilmycin (8 mg L(-1)) and Paromomycin sulphate (6 mg L(-1)) was proposed. The enzymatic profile patterns of different bifidobacterial species and strains were inhomogeneous and could, therefore, not be used as selective detection criteria. Finally, the applicability of the medium was evaluated by examining different bifidobacteria-containing dairy products under practical conditions.