262 . THE OUTLOOK FOR THE FUTURE 



7. probably in gas gangrene, but here numbers have been few and meth- 

 ods not fully tried out."* 



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 some fifty compounds or preparations possessing bacterio- 

 static and fungistatic properties have already been isolated from micro- 

 organisms, there is sufficient evidence that many more can be obtained 

 without too great difficulty, if enough organisms are studied in greater 

 detail. In this connection, three methods of approach have been fol- 

 lowed: (a) testing organisms found in culture collections for antibac- 

 terial 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. notatumr-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 organ- 

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

 bacteria, followed by the isolation of organisms capable of inhibiting the 

 growth of or of destroying such bacteria. 



Several surveys (26, 282, 504, 628, 644, 934, 936, 986) have already 

 been made concerning the distribution of organisms capable of produc- 

 ing antibiotic substances among certain groups of bacteria and fungi. 

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

 gation. The reasons for this are quite obvious and are based largely 

 upon the great amount of time and experimentation required for the 

 isolation of any one substance. The selection of a particular substance 

 was largely governed by its specific antibiotic spectrum, or its activity 

 upon particular bacteria, its toxicity to animals, and its activity in vivo. 

 The following illustrations will suffice: 



Of all the aerobic spore-forming bacteria known to produce anti- 

 biotic substances, only B. brevis has been utilized for the isolation of 



* Further information on this subject is found in the various reports listed in Chapter 12 of 

 this book and in a group of papers presented before a symposium on antibiotic agents (65, 163, 

 189, 399a). 



