Patent ID: 8021883

Claim:
A method for obtaining a tetracycline-sensitive Bifidobacterium strain, said method comprising: (a) subjecting a progenitor culture of a Bifidobacterium strain to a chemical mutagen and a physical mutagen; then (b) isolating Bifidobacterium cells that are sensitive to a tetracycline from said progenitor culture; and (c) culturing at least one tetracycline-sensitive cell of step (b) to obtain a tetracycline-sensitive Bifidobacterium strain, wherein said progenitor strain has a functional tetW gene and said tetW gene is inactivated in the obtained tetracycline-sensitive strain, and wherein said tetracycline-sensitive strain has a Minimum Inhibitive Concentration to tetracycline of 1.5 μg/ml or less.