10 Bifidobacterium strains and 10 Lactobacillus strains were studied for their antagonistic activity with respect to Escherichia coli, Klebsiella ozaenae, Staphylococcus aureus, Enterococcus faecalis, Pseudomonas aeruginosa and for their sensitivity to antibiotics, widely used in clinical practice. L. acidophilus strain 5/4, L. acidophilus strain 18/4, B. adolescentis strain UX, B. longum strain 44 exhibited the highest antagonistic activity and the highest degree of antibiotic resistance. The restriction analysis of the chromosomal DNA of these strains was then made and their plasmid content was studied, making it possible to recognize these strains in future in the course of in vivo experiments.