The Soil as a Source of Microorganisms Antagonistic to Disease-Producing Bacteria

Abstract

A new method of determining the abundance in soil of organisms antagonistic to specific bacteria is descr.; it involves use of a washed agar medium in which the viable cells of the bacteria in question form the sole source of nutrients. Using this method, it was demonstrated that the soil contains several types of microorganisms antagonistic to various bacteria belonging to the gram-positive and gram-negative groups. By enriching the soil with the specific bacteria, the corresponding antagonists increase and can readily be isolated. Of several antagonistic organisms isolated from the soil 2[long dash]a bacterium belonging to the Pseudomonas aeruginosa group and an Actinomyces were studied in detail. These organisms inhibit the growth of several gram-negative bacteria, as well as numerous gram-positive bacteria even to a greater extent. The active substance produced by the 2 antagonists was largely thermostable; it passed through a Seitz filter. was removed by charcoal and was at least partially ether-soluble. Highly active prepns. were obtained which inhibited, in very dilute solns., the growth of Escherichia coli, Brucella abortus, and of many other bacteria. It also had a strong bactericidal effect and reduced even in very low concs., the bacterial population of various natural substrates, such as milk.