Abstract: To study the relation between antibiotic resistance and plasmids for Bifidobacteria, experiments as below were conducted. With Staphylococcus aureus ATCC 25923 as the control bacterium, the antibiotic susceptibility patterns of 10 strains of adhesive Bifidobacteria were tested by the agar diffusion method. Twelve groups of antibiotics, thirty-eight kinds in total, are involved in the testing. Also the plasmids of the strains tested were extracted by using the alkaline lysis method. The results showed, the same strain exhibited accordant sensibility to the antibiotics of the same group; different strains tested shared great coincidence to the same group of drugs. Nearly all of them were resistant to penicillin group, quinoline group, aminoglycoside group and peptide group, while showing sensitivity to cephalosporin group, macrolide group, sulphonamide group, chloram- phenicol and clindamycin. There were also differences existed between the strains of different origins. Analysis of the plasmid DNA from 10 strains of Bifidobacteria, revealed that the number of plasmid DNA was only one for strain H-3, and that the size of the isolated plasmid DNA was in the range of 5148bps to 21226bps,with no plasmids DNA found in the other Bifidobacterial strains tested.

Key words: Bifidobacteria, antibiotic susceptibility, plasmid DNA