Both B. bifidum YIT 4001 and YIT 4007 show resistance to streptomycin
at the concentration lower than 25 μg/mL. The MIC of B. bifidum
YIT 4007 for streptomycin was superior to 50 μg/mL, and the MIC of B.
bifidum YIT 4001 for streptomycin was inferior to 50 μg/mL. Streptomycin
resistantmutantswere isolated fromthree independent clones at
the frequency of 10−8 to 10−9 similarly to neomycin resistant mutants
except that 500 μg/mL of streptomycin sulfate (Sigma) was used.