318 OUTLOOK FOR THE FUTURE 



novyi and Leftosfira icterohaemorrhagka. Following the oral or 

 parenteral administration of streptomycin, no unfavorable effects have 

 been encountered which could not be attributed largely to the presence 

 of impurities in the preparations. To date, streptomycin has been ad- 

 ministered for infections of the urinary tract, typhoid, brucellosis, 

 Klebsiella infections, tularemia, tuberculosis, and wounds." 



It appears, therefore, that certain generalizations concerning possible 

 future developments in the field of antibiotic substances are justified. 



A SEARCH FOR NEW ANTIBIOTIC AGENTS: 

 A PROBLEM FOR THE MICROBIOLOGIST 



Although more than sixty compounds or preparations possessing bac- 

 teriostatic and fungistatic properties have already been isolated from 

 microorganisms, there is sufficient evidence that a great many others 

 can be obtained without too great difficulty, if enough organisms are 

 studied in greater detail. In this connection, three methods of approach 

 have been followed: (a) testing organisms found in culture collections 

 for antibacterial activity in general, followed by a detailed study of one 

 or more substances produced by one or more organisms j (b) isolating 

 specific organisms, such as members of the P. notatun-ir-P . chrysogenum 

 groups, from different soils and from moldy food materials and testing 

 them for the production of penicillin, in the hope of finding more active 

 organisms than those now known to exist j (c) enriching the soil with 

 specific bacteria, followed by the isolation of organisms capable of in- 

 hibiting the growth of or of destroying such bacteria. 



A summary of the various steps essential to the isolation of a suitable 

 chemotherapeutic agent are given in Figure 34. A number of surveys 

 have now been made concerning the distribution of organisms capable 

 of producing antibiotics among bacteria, actinomycetes, and fungi. 

 Only very few such organisms were selected for more detailed investi- 

 gation, chiefly because of the great amount of time and experimentation 

 required for the isolation of any new type of substance. The selection of 

 a particular antibiotic for isolation and further study is largely gov- 

 erned by its specific antimicrobial spectrum, its action upon particular 



