Bifidobacteriumbifidumstrain Yakult YIT 4007 (abbreviated as B. bifidum
YIT 4007 below) is a commercial strain which is utilized to produce a
fermented milk beverage. This strain was isolated sequentially by
stepwise screenings of mutants resistant to erythromycin, neomycin,
and streptomycin fromits progenitor strain B. bifidumYIT 4001 tomake
it easily distinguishable fromother Bifidobacteria. Thus, genetic bases of
these antibiotic resistances are very important to elucidate the nature of
the antibiotic resistance of B. bifidum YIT 4007 because the product
containing this strain is ingested by consumers on a daily basis