B. bifidumYIT 4001was used for the isolation ofmutants resistant to
antibiotics. The MIC (Minimal Inhibitory Concentration) of B. bifidum
YIT 4007 for erythromycin on MILS lactose broth was superior to
5000 μg/mLwhereas theMIC of B. bifidumYIT 4001 for erythromycin on
the same broth was inferior or equal to 0.1 μg/mL. B. bifidum YIT 4001
cells grown on MILS lactose broth were spread on TOS-propionate agar
containing 0.1 μg/mL erythromycin (Abbott Japan, Osaka, Japan), and