[Response, to polymyxin, of plague microbe strains isolated from various natural foci and of their mutants with a decreased requirement in nutritional factors].

Investigation of the response to polymyxin of 65 strains of Pasteurella isolated from various foci and 46 their back mutants showed that all of them were usually highly resistant to polymyxin (MIC 200--500 micrograms/ml). The Pasteurella strains isolated in the Gissaro-Darvaz natural focus, Turkey and Congo were highly sensitive to polymyxin (MIC 10--25 micrograms/ml). Single cultures highly sensitive to the antibiotic were detected among the polymyxin-resistant strains. Polymyxin-sensitive mutants of these cultures with lowered requirements in the growth factors were obtained.