MORPHOLOGICAL AND PHYSIOLOGICAL INVESTIGATIONS ON ACTION OF POLYMYXIN B ON ESCHERICHIA COLI

Cultures of Escherichia coli (exponential phase of growth) were exposed to various concentrations of polymyxin and studied with different methods. Viable counts showed that the effect of polymyxin depends on the antibiotic concentration, on the density of the bacterial suspension and the duration of treatment. Measurements of the oxygen consumption have shown that the polymyxin effect begins immediately after addition of the substance and reaches its highest intensity after about 10 to 15 min. For electronmicroscopical studies controls and treated bacteria were fixed according to Ryter and Kellenberger (1958), and stained with uranyl acetate. Embedded in vestopal or methacrylate. The influence of polymyxin on the substructure of the coli cells at a suspension density of 1.2 mg wet weight of bacterial/ml can be devided into 2 phases: polymyxin concentrations up to 10 μg/ml produce protuberances at the cell surface the number of which increases with increasing concentration of the antibiotic, but they cause little intracellular changes. Polymyxin doses exceeding 10 μg/ml produce, besides the formation of protuberances, a rapidly proceeding cell autolysis which becomes manifest firstly by a brightening of the nuclear area and then by destruction of the whole cytoplasm. It is probable that the moment of formation of the first protuberances coincides with the cell death. © 1968 Springer-Verlag.