Studies on Polymyxin: An Agar Diffusion Method of Assay

Abstract

The factors affecting the size and quality of the zone of inhibition in agar of Escherichia coli produced by the antibiotic polymyxin are descr. Under suitable conditions a linear relationship exists between conc. of polymyxin (plotted logarithmically) and diam. of zone over a range of at least 1 to 256 U./ml. A filter paper-disk method of assay is presented in detail together with a statistical analysis and a method for determining the error of any assay.