MICROBIAL ANTAGONISMS AND PRODUCTION OF ANTIBIOTICS 



II 



ill nature. The useful aiitil)i(>tics, which are 

 mainly the product of the metabolism of 

 actinomycetes, fungi, and bacteria, are not 

 natural products in the same sense that 

 (juinine is. It is possible to collect l)ark from 

 Cinchona trees in naturally occurring stands 

 and to extract from this bark commerciall.y 

 useful (luinine. It is not possible to extract 

 soil and isolate from the extract chloram- 

 phenicol or any of the other important anti- 

 biotics. Antil)iotics as we know them are 

 laboratory products obtained by growing 

 pure cultures of microorganisms under nu- 

 tritionally rich and well aerated conditions 

 not to be found in the soil. 



The difference between the ease of ex- 

 tracting ciuinine from a tree grown under 

 conditions unaltered by man and the im- 

 possibility of extracting chloramphenicol 

 from Streptomyces venezuelae naturally oc- 

 curring in a normal soil may be only a re- 

 flection of the differences in the physical 

 size of the tree, the actinomycete, and man. 

 The actinomycete in a natural soil sample 

 is indeed a needle in a haystack. 



The possibility then remains that small 

 amounts of antibiotics may play a role in 

 the microcosm that surrounds the hyphae 

 of the antibiotic-producing organism. These 

 antagonistic interactions would probably be 

 more pronounced in the vicinity of accumu- 

 lated organic matter. At present, as can be 

 seen from the excellent discussion of Brian 

 (IQoT), too little solidly grounded informa- 

 tion is available to warrant much more than 

 speculation about the ecological significance 

 of antibiotic production. 



Production of Antibiotics by Actino- 

 mycetes 



Be that as it may, the actinomycetes are 

 prolific antibiotic-producers in . the labora- 



tory and the factory. The compilation of 

 antibiotics of actinomycetes in Part B of this 

 book includes the listing and description of 

 some 400 chemical substances and prepara- 

 tions. Alost of these were found in the cul- 

 ture broths of various organisms and a few 

 in the mycelium. These substances and 

 preparations vary greatly in their physical 

 and chemical properties, antimicrobial ac- 

 tivities, toxicity to animals, and chemo- 

 therapeutic potentialities. 



About 80 antibiotics produced by actino- 

 mycetes have already found extensive ap- 

 plication ill the treatment of various human 

 and animal diseases. These include strepto- 

 mycin and its derivative dihydrostrepto- 

 mycin, chloramphenicol, the tetracyclines, 

 ^'iomycin, neomycin, cycloserine, erythro- 

 mycin, no\T)biocin, oleandomycin, kanamy- 

 cin, A-ancomycin, cycloheximide, nystatin, 

 amphotericin B, trichomycin, and paromo- 

 mycin. They are used in the treatment of a 

 great variety of infections caused by gram- 

 positive and gram-negative bacteria, myco- 

 bacteria, rickettsiae, the members of the 

 psittacosis-lymphograiiuloma group of intra- 

 cellular parasites, trichomonads, amoelxie 

 and other protozoa, monilia and other fungi. 

 Some antibiotics, such as streptomycin and 

 cycloheximide, have found application in the 

 treatment of plant diseases. Some are used in 

 animal feeding. Some, like the tetracylcines, 

 have found application in the preservation of 

 poultry and certain other foodstuffs. This 

 wide range of usefulness makes the actino- 

 mycetes the most important of all the anti- 

 biotic-producing microorganisms. Only four 

 fungal products (penicillin, fumagillin, vari- 

 otin, and griseofulvin) and three bacterial 

 products (bacitracin, polymyxin, and tyro- 

 thricin) are used in medicine. 



