Ten strains of plasmid-harboring Bifidobacterium sp. were isolated from the feces of adults and children, and named as Bifdobacterium sp. GE1-GE8, ST, and SH5. These plasmids were categorized into three homologous groups (pKJ50-homologous, pKJ36-homol...
Ten strains of plasmid-harboring Bifidobacterium sp. were isolated from the feces of adults and children, and named as Bifdobacterium sp. GE1-GE8, ST, and SH5. These plasmids were categorized into three homologous groups (pKJ50-homologous, pKJ36-homologous, and non-homologous groups) according to Southern hybridization patterns using the formerly characterized bifidobacterial plasmids, pKJ50 and pKJ36, as probes. Nine strains harboring the plasmids were shown to accumulate single-stranded DNA as a replication intermediate, based on the S1 nuclease treatment and Southern hybridization. These results suggest that the strains replicate by a rolling circle mechanism. Minimal inhibitory concentrations (NEC) of the isolated bifidobacteria against several antibiotics were determined. Two strains, GE2 and GE3, showed relatively high MIC values against tetracycline (793.6㎍/㎖) and erythromycin (153.6㎍/㎖), respectively. The tetracycline resistance of GE2 disappeared when the resident plasmid of GE2 was cured by ethidium bromide. These results show that pKJ36-homologous and pKJ50-homologous plasmids are prevalent among various Bifidobacterium strains and some BWdobacterium plasmids appear to code for antibiotic resistance.