Plate Methods for Testing Antibiotic Activity of Actinomycetes against Virulent Human Type Tubercle Bacilli

Abstract

The streak plate method using the virulent type of tubercle bacillus (H37Rv) is useful for the testing of the antibiotic properties of actinomycetes. This gives a relatively rapid method for screening cultures in a search for new antibiotics. If a streptomycin-resistant strain of H37Rv is also streaked on the plates, cultures bearing a relationship to Streptomyces griseus may be detected. A smooth, opaque layer of growth may be obtained by seeding pour-plates with H37Rv. Filtrates and concentrates in cups will give inhibition zones, though quantitative measurements are difficult to make because the zones are not always sharply defined. Pour-plates, seeded with tubercle bacilli and streaked with actinomycetes, are useful in the search for cultures with tuberculostatic properties. The plates may be seeded with H37Rv or with H37RvR (resistant to streptomycin) and cross-streaked with various strains of actinomycetes. The avirulent, rapidly growing strain 607 is not suitable for this purpose, Since some strains of actinomycetes which inhibit the virulent H37Rv strain do not inhibit, under the same conditions, strain 607.