The effect of reducing agents on the recovery of injured Bifidobacterium cells.

Bifidobacterium spp. have been proposed as a microbial indicator of faecal pollution in water and as possible probiotic in fermented dairy products. These anaerobic bacteria can be subject to metabolic stress in environmental samples because of the presence of oxygen or its derivatives. In this case, their recovery is compromised, especially in selective media. Three reducing agents were tested to improve the recovery of oxygen-stressed bifidobacteria: L-cysteine, sodium pyruvate and sodium thioglycolate. These agents were evaluated individually at various concentrations, and in combination by measuring recovery on rich and selective media. The addition of several mixtures of reducing agents to the water samples and pre-incubation for 4 h at 37 degrees C increased the recovery of Bifidobacterium spp. on culture media.