Note. In Vitro Viability of Bifidobacterium Strains Isolated from Commercial Dairy Products Exposed to Human Gastrointestinal Conditions

Abstract

Levels of bifidobacteria contained in commercial fermented milks in Spain were determined by fluorescent techniques. The transit tolerance of probiotic bifidobacteria strains to human gastrointestinal tract (GIT) was assessed in vitro. The number of bifidobacteria in commercial fermented milks declared to contain bifidobacteria varied from 104 to 107 bacteria/m L. Viable cell counts estimated by plating onto selective media were lower than direct counts. Bifidobacteriumstrains analysed showed different survival behaviour. Viable bacteria counts decreased considerably following exposure to gastric juice. As only intrinsic acid resistant cells survive their passage through the human intestine, the selection of acid tolerant strains is necessary for the elaboration of probiotic products. Viability of dairy bifidobacteria is affected by gastrointestinal juices but the majority of tested strains survived well at gastrointestinal conditions. The reason for this may be the low number of viable bifidobacteria contained in commercial dairy products. Adaptation and survival at low pH is likely to determine the efficacy of Bifidobacterium strains both as dairy starters and probiotic microorganisms. This study confirmed the usefulness of fluorescent techniques for a rapid and accurate evaluation of bacterial viability in probiotic products.