EN
Observations were made of resistance acquirement to some antibiotic combinations, under laboratory conditions, by E. coli and Salmonella microorganisms. It has been found out that the strains resistant to some particular antibiotics proved susceptible to their combinations; the strains with already acquired resistance to the examined combinations proved to be susceptible to their components to a various degree. During combined application of streptomycin with Oxytetracycline or penicillin a slower resistance acquirement, in vitro, by the examined bacteria has been found out in comparison with that observed during the use of some particular components. In the in vivo studies, performed in mice, a relationship has been found between the resistance in vitro and a therapeutic effect.