Selective Isolation and Enumeration of Actinomycetes using Rifampicin

Addition of rifampicin (5µg/ml) to a number of media allowed the selective isolation of Actinomadura strains from soil and enabled large numbers of ‘Thermomonospora (Thm.) chromogena’ and Streptomyces (St.) albus to be isolated from hay and straw. Saccharomonospora (S.) viridis was also tolerant to the antibiotic but was often inhibited by other isolates, while other bacteria including Micropolyspora faeni, ‘Thm. fusca’, Thermoactinomyces (Tha.) vulgaris and some other Streptomyces spp. were mostly sensitive, even to 2·5 µg/ml. Heating soil samples at 100°C for 15 min further decreased the number of unwanted bacteria growing on glucose-yeast extract agar supplemented with 5 µg/ml of rifampicin.