Chapter VII 



— 119 — 



Antagonistic Properties 



show certain similarities in chemical nature and in their general anti- 

 biotic spectra; they differ in their toxicity to animals, in their selective 

 action upon certain bacteria, such as B. mycoides and S. marcescens, 

 and in the greater action of streptomycin upon M. Uihercidosis haminis. 

 Some of the antimicrobial spectra are very narrow, as shown by the 

 so-called antismegmatis factor, which is active only against M. s^neg- 

 luatis and certain other mycobacteria (215). On the other hand, strep- 

 tomycin itself is produced, not only by S. griseiis, but also by S. hikini- 



Table 23 : Inhibition of different actinomycetes by their respective antibiotics (475) : — 



ensxs (194, 195). Streptothricin or similar substances are produced 

 by a large number of organisms.- These substances show certain quanti- 

 tative differences in their action upon different bacteria, in their activity 

 upon fungi, in their toxicity to animals, and in certain chemical charac- 

 teristics. Usually an organism producing a certain antibiotic is resistant 

 to its antimicrobial action (Table 23). 



Methods of isolation and testing.— In a search for antibiotics pro- 

 duced by actinomycetes, several steps are followed, namely, 



1. The soil or other natural substrate is plated out on suitable media and the 

 colonies of actinomycetes are picked and transferred to slants. 



2. The cultures are tested by the agar-streak method (Fig. 24), using a series 

 of test bacteria. Those that are found to possess the highest or more desirable 

 properties are selected. 



3. The selected cultures are grown on suitable media, under stationary and 

 submerged or shaken conditions, and antibiotic spectra of the metabolite solution 

 determined. 



4. After suitable media and culture conditions have been established, for a 

 particular organism, it is grown until a large quantity of the metabolic solution is 

 obtained. 



5. Methods are now developed for the isolation, concentration, and purification 

 of the antibiotic. 



6. The purified antibiotic is now studied for its chemical and physical, as well 

 as its antimicrobial properties, since the antibiotic spectrum of the isolated anti- 

 biotic may not correspond to that of the metabolite solution. 



7. The antibiotic is now tested for its toxicity to animals and its in vivo 

 activity. 



