Studies on polymyxin: isolation and identification of Bacillus polymyxa and differentiation of polymyxin from certain known antibiotics

Polymyxin is an antibiotic substance occurring in the culture filtrates of Bacillus polymyxa. The isolated substance is unique in its specificity for gram-negative bacteria. A summary of the more important results obtained during the course of several years, including chemotherapeutic and toxicity data, has been reported (Stansly, Shepherd, and White, 1947). The present contribution is concerned with the isolation and identification of the antibiotic-producing organism and some early findings which both characterized and distinguished polymyxin from certain known antibiotics. Isolation of Bacillus polymyxa. Bacillus polymyxa was isolated from soil in the course of a program designed to find new antibiotics for the chemotherapy of gram-negative bacterial infections. The test organism used in this search was Salmonella schottmuelleri. Our method for isolating antibiotic-producing organisms with a specific type of activity involves the preparation of pour plates of soil dilutions using a variety of media and cultural conditions. The plates are subsequently sprayed with a suspension of the test organism by mean