Chapter VII 



— 129 — 



Antagonistic Properties 



are more variable in this respect than others and give rise continuously 

 to strains that appear to be physiologically different, or at least to vary 

 in their quantitative production of streptomycin. The fact that inactive 

 strains are sensitive to streptomycin, whereas the streptomycin-producing 

 cultures are resistant, would tend to bring about the continuous self- 

 purification of streptomycin-producing strains from the nonproducing 

 strains, as long as they are growing under conditions favorable to strep- 

 tomycin production. 



Production of other antibiotics by actinomycetes.—A number of 

 other antibiotics are known to be produced by actinomycetes (482). 

 Some have been crystallized; others ha\'e ne\'er been obtained in even a 

 concentrated form. Some have wide antibiotic spectra; others act only 



Table 29: Antibiotic spectra of streptomycin, streptothricin, and antibiotic 136 (40): — 



* This preparation assayed 150 £. coli uni 

 streptothricin should he divided by 8 to make 

 rations. 



On the basis of this comparison, the units for streptomycin an( 

 comparable with standard streptomycin and streptothricin prepa 



against very few organisms. There is also a marked difference in their 

 chemotherapeutic potentialities. 



Some of the antibiotic-producing organisms are widely distributed 

 in nature. This is true particularly of such groups as S. lavendulae 

 and S. griseiis. One would expect that some of the strains of these 

 organisms would produce antibiotics which differ in chemical structure 

 and, therefore, in their biological activities. Attention has already been 

 called to the fact that some antibiotics actually obtained from different 

 organisms may either represent a mixture of compounds or a single type 

 compound, which varies, however, in its antibiotic spectrum and in its 

 toxicity to animals. This variation depends upon the strain of organism 

 producing the antibiotic, composition of the medium in which it is 

 produced, and conditions of growth. This can be illustrated by antibio- 

 tic 136, which is produced by a strain of S. lavendnlae, but which differs 

 frc^m streptothricin in its antibiotic spectrum, in toxicity to mice and in 

 the ratio of activity in broth and in agar (Table 29). 



