[Resistance to nalidixic acid in tetracycline-resistant mutants of E. coli]

The studies on the effect of nalidixic acid (negram) on the synthesis of DNA and determination of its minimal inhibitory concentrations revealed a regular decrease in the sensitivity levels to negram of the tetracycline resistant mutants selected on media with tetracycline. Heterogene ty of the tetracycline resistant mutants to EDTA showed that one of the causes of insensitivity of the mutants to negram was a change in the surface structures of the microbial cell.