Actinomyces antibioticus, a New Soil Organism Antagonistic to Pathogenic and Non-pathogenic Bacteria.

In a search for microorganisms antagonistic to bacteria, especially to the gram-negative ones, the bacterial-agar plate method was used (Waksman and Woodruff, 1940a). This consists in adding a suspension of washed living bacteria to 1.5 per cent sterile washed agar containing 0.5 per cent NaCl and 0.5 per cent K2HPO4. To a fresh field or garden soil, or one previously enriched several times with washed centrifuged suspensions of the bacteria in question, is added sterile tap water, to give a series of dilutions; 1 ml. of each dilution is placed in a sterile plate and the bacterial agar added. If the soil contains specific antagonists, their colonies are usually surrounded by clear zones, in which the cells added to the agar have been killed. By the use of the foregoing method, using suspensions of Escherichia coli or Aerobacter aerogenes,2 several antagonistic organisms were isolated, comprising both bacteria and actinomycetes. One species of Actinomyces proved to be particularly active against a great variety of bacteria and fungi. It was found to produce a specific bacteriostatic and bactericidal substance,