Chapter VII 



— 121 — 



Antagonistic Properties 



active against bacteria over a wide pH range with an optimum at slight 

 alkalinity. It is also active in vivo against various bacteria and fungi. 

 It is not active against viruses. It is resistant to the action of different 

 microorganisms and to enzymes. Unfortunately, it leaves in the animal 

 body a residual toxic effect which precludes its parenteral administra- 

 tion and limits its use to oral or topical applications. 



The experience gained in the study of streptothricin proved to be 

 suggestive in planning a search for other antibiotics that would possess 

 similar or even more desirable biological and chemical properties and 

 that would be less toxic to the animal bodv. After an extensive ex- 



Table 25: Inhibition of grotvth of i indent huviati tubercle bacilli 

 by different actinomycetes (510) : — 



Inhibition, in millimeters, by agar streak method 



* Streptomycin-sensitive strain of M. tuhenulosis . 

 t Streptomycin-resistant strain of M. tuberculosis. 



amination of many cultures of actinomycetes, representing a number of 

 species and strains, two freshly isolated cultures of an organism similar 

 to one isolated from the soil in 1916 and described as Actinomyces 

 CStre^toviyces} griseus (460) were obtained and were found to yield 

 an antibiotic which did not possess the toxicity of streptothricin and had 

 an even broader antibacterial spectrum. Since the generic name of this 

 group of actinomycetes had recently been changed from Actinomyces to 

 Streftoviyces (467), the new antibiotic was called streptomycin. Dif- 

 ferent strains of S. griseus were later found to vary greatly in their 

 ability to produce streptomycin and in their sensitivity to this anti- 

 biotic. The course of growth of this organism, change in the con- 



