Formation of a mixture of antibiotic substances including antibiotics of a polyene character, by strains of actinomycetes freshly isolated from soil samples

Of a total of 739 actinomycetes freshly isolated from soil samples from China, 515 (69·7%) were antibiotically active. Their antibiotic spectrum was determined against 14 test micro-organisms, including bacteria, yeasts and fungi, and 386 of them were characterized by paper chromatography using agar blocks, by behaviour on agar plates incorporating ion-exchange resins and by u.v. absorption spectrum (to detect polyene substances). Of these strains, 195 (50·5%) produced a mixture of antibiotics of both polyene and non-polyene type. On the basis of these results the active strains have been classified in various ways.