We have recently determined the whole genome sequence of B.
bifidum YIT 4007 and found no mobile genetic factors on the chromosomal
regions around ribosomal RNA, rluD, and rpsL genes (unpublished).
The whole genome sequence of B. bifidum 4001 was also
compared with that of B. bifidum YIT 4007 using the Comparative
Genome Hybridization array analyses. Twenty four mutations were
identified on B. bifidum YIT 4007 chromosome in addition to five
mutations of 23S ribosomal RNA, rluD and rspL genes, and all these
mutations were single base substitutions (Ishikawa, personal communication).
But none of these 24 mutations was not commonly
distributed among antibiotic resistant mutants newly isolated from B.
bifidum YIT 4001 (unpublished) suggesting no involvement of 24
mutations in antibiotic resistance of B. bifidum YIT 4007. Resistances to
erythromycin, neomycin, and streptomycin of B. bifidum YIT 4007 were
very seemingly caused by mutations of indigenous genes and were
not associated with mobile genetic elements like insertion sequences,
phages, and plasmids.