46 



THE ACTINOMYCETES, Vol. I 



obtained tends to establish the fact that in a 

 natural soil, in the presence of the numerous 

 competing forms of life, no antibiotic is pro- 

 duced; were the reverse to be the case, the 

 antibiotics would have played an important 

 part in the distribution of various groups of 

 microorganisms in the soil. Only among the 

 actinomycetes do we find a large proportion 

 of organisms capable of producing antibiot- 

 ics. One could have expected a much greater 

 number of organisms in the soil, notably 

 among the bacteria, to be resistant to the 

 particular antibiotics. 



4. All attempts to isolate specific anti- 

 l)iotics from, or to demonstrate their pres- 

 ence in, the soil have so far failed. In those 

 few instances where antimicrobial acti\'ities 

 have been demonstrated in the soil, it is still 

 uncertain whether antibiotics are present 

 there as such, and if so, whether they are of 

 microbial or plant origin, how they have 

 been formed there, and of what significance 

 they are in modifying the native population 

 of the soil. Such activities may actually be 

 due to various plant products left in the soil 

 as a result of the decomposition of plant 

 residues, such as tannins, oils, resins, or lig- 

 nins and lignin derivatives. 



5. Enrichment of a fresh natural soil with 

 living cultures of microorganisms has failed 

 to stimulate or favor the selective develop- 

 ment of other organisms that would be capa- 

 ble of producing antibiotics active against 

 the organisms introduced. Antibiotics are 

 not enzymatic systems that are stimulated 

 by the addition of special nutrients. Earlier 

 claims of the favorable effects of additions 

 of microbial cultures in enriching the de- 

 velopment of antibiotic-producing organisms 

 have not been confirmed on further study. 



6. When pathogenic and even saprophytic 

 bacteria are introduced into fresh soil oi' into 

 fresh sea water, they do not nniltipl}^ in the 

 new enviromnent, but tend to die out rap- 



idly. Although this was originally ascribed 

 to the presence in the soil or in the sea of 

 antibacterial substances, comparable to an- 

 tibiotics, the actual facts have not substan- 

 tiated this explanation. Such substances are 

 usually removed on sterilization, whereas 

 many of the antibiotics are resistant to heat. 

 It may, of course, be argued that the disap- 

 pearance of cultures of organisms added to 

 soil or water is due not so much to the pres- 

 ence of antibacterial substances as to the 

 competition of the organisms capable of pro- 

 ducing such substances. This explanation 

 begs the main ciuestion, however, whether 

 the formation and accumulation of antibiot- 

 ics can take place at all under natural con- 

 ditions. 



The following illustration may be pre- 

 sented in support of the foregoing state- 

 ments. Considerable information has recently 

 been accumulated on the disturbed micro- 

 biological population in the animal digestive 

 system due to the consumption of antibiot- 

 ics. Of particular interest in this connection 

 are the effects of products of metabolism of 

 actinomycetes, such as streptomycin, chlor- 

 amphenicol, and the tetracyclines, upon the 

 intestinal population of animals. Streptomy- 

 cin is known to favor the rapid development 

 of resistance among the sensitive bacteria. 

 Baumgartel succeeded in extracting desoxy- 

 ribonucleic acid from resistant strains and 

 transplanting it to sensitive strains. Sensi- 

 tivity and resistance of an organism to a 

 given antibiotic thus depend upon the chemi- 

 cal composition and the metabolic mecha- 

 nisms of the organisms concerned rather 

 than upon a dialectic concept of "struggle 

 for existence." The possibility that the lo- 

 calized production of antibiotics on plant 

 residues may be of ecological significance is 

 not (>xcluded, however, as shown by Brian 

 (1057). 



