Provided are a method for constructing a bacterium belonging to the genus Bifidobacterium which shows excellent survival even under conditions with different environmental factors, the novel bacterium belonging to the genus Bifidobacterium constructed by said method, and a method for detecting said bacterium.By alternately conducting subcultures and preservations in systems under such conditions as differing from each other in environmental factors, a bacterium belonging to the genus Bifidobacterium, which shows excellent survival under all of the conditions employed in the alternate subcultures and preservations, can be constructed.
