Waksman — 120 — Actinomycetes 



Such simple procedures as the agar streak method can be used for 

 screening purposes. The nature of the medium is of great importance, 

 however, as shown in Table 24. Although for most practical purposes, 

 it is sufficient to use ordinary saprophytic bacteria as test organisms, it 

 may become advisable to use in certain cases pathogens. This is true 

 particularlv in the search for organisms active against the tuberculosis 

 organism. Williston, Zia-Walrath and Youmans (510) have 

 shown, for example, that for screening of actinomycetes for their anti- 

 tuberculosis activities, the avirulent, rapidly growing strain 607 of M. 

 tuberculosis is not suitable; some strains of actinomycetes which inhibit 



Table 24: Distribution of antagonistic properties among actinotnycetes (194): — 

 Cross-streak method. Numbers reported in per cent of total cultures. 



the virulent H37Rv do not inhibit, under the same conditions, strain 

 607 (Fig. 23fl and Fig. 2'h¥). The nature of the medium is also of 

 great importance, as shown in Table 25. 



Isolation of streftothricin and streptomycin.— Streptothricin was the 

 first substance that appeared to show distinct promise as a chemothera- 

 peutic agent, since it was not very toxic to animals, and especially since 

 it was active against gram-negative bacteria. It was obtained (493) 

 from a culture of an organism found to be identical with Actinomyces 

 CStreptomyces^ lavendulae that had been isolated in the same labora- 

 tory, from the soil, in 1916 (443,460). The name was derived from 

 Streptothrix, as the actinomycetes were designated bv Ferdinand Cohn 

 in 1875. Other strains of the S. lavendidae group were later isolated and 

 found capable of producing streptothricin or closely related antibiotics 

 (179a, 204, 215). 



Streptothricin is water-soluble and fairly resistant to heat, and is 



