NATURE, FORMATION, AND ACTIVITIES 



antibiotic, microbes usually become resistant 

 to this antibiotic as a result of the selection, 

 by the antibiotic, of resistant mutants. 



The potentiality of a particular antibiotic 

 for important therapeutic usefulness in th(> 

 treatment of one or more infectious diseases 

 depends largel^^ upon its action on the causa- 

 tive agents of the disease and its lack of 

 toxicity to the affected animals or plants. 

 There are very few infectious diseases now 

 known, aside from those caused by viruses 

 and certain protozoa and some fungi that 

 are not completely or partly controlled by 

 the use of antibiotics. Nearly all the dis- 

 eases caused by bacteria, and some of the 

 diseases caused by fungi, rickettsiae, and 

 the psittacosis-lymphogranuloma group of 

 organisms, certain amoebae, and trichomo- 

 nads, lend themselves readily to antibiotic 

 therapy. Such diseases include not only those 

 that afflict man, but also those that attack 

 animals and plants. 



Some antibiotics also possess a marked 

 growth-promoting effect upon animals and 

 have thus found practical application in the 

 nutrition of these animals. This is true es- 

 pecially of nonruminant animals, such as 

 swine and poultry. Ruminant animals are 

 usually excluded, since antibiotics may 

 affect adversely the bacterial population of 

 the rumen which assists such animals in the 

 digestion of cellulosic food materials; but 

 even some of the ruminant animals may 

 benefit at a certain stage of their develop- 

 ment from the use of antibiotics. Antibiotics 

 at low concentrations may exert a growth- 

 promoting effect also upon certain microbes. 

 This effect becomes growtli-inhibiting and 

 even destructive at higher concentrations; 

 hence, the concentration in which antibi- 

 otics are used is of prime importance. 



Because of their specific selective action 

 upon microbial cells, antibiotics are ideal 

 agents for the preservation of semen, A'irus 

 preparations, vaccines, and similar biological 

 materials. Hecently, antibiotics have been 



utilized foi- the j^reservation of foods, es- 

 pecially poultry and certain vegetables. 

 Since a single antibiotic will not inhibit all 

 forms of mici'obial life, more than one anti- 

 biotic may be recjuired. Before the food is 

 eaten the antibiotics must be inactivated, 

 as by boiling, since their constant consump- 

 tion in the food might exert dangerous effects 

 upon the human body. 



The potentialities in the utilization of 

 antibiotics in the life of modern man are 

 still far from exhausted. Wherever man has 

 had to combat microbes — be they injurious 

 to his own health or to that of his herds and 

 crops or be they destructive to his industrial 

 products or to his foodstuffs — he has found 

 and will continue to find in the antibiotics 

 a source of great assistance. 



Howe\'er, as with every other great dis- 

 covery that has revolutionized human life, 

 new problems have arisen as a result of the 

 usage of antibiotics. The prevalence of cer- 

 tain microbes resistant to specific antil)iotics 

 is now a major problem of chemotherapy. 

 As resistant forms appear, new antibiotics, 

 or new forms of known antibiotics, have to 

 be found to eradicate them. This seems to 

 he an endless process. The problem might be 

 minimized by a rotation program in the 

 usage of antibiotics. The disturbance in the 

 microbiological e(iuilibrium existing in na- 

 ture by the extensive use of chemical agents 

 that tend to eliminate certain members of 

 the microbial population and not others may 

 not only stimulate the de\'elopment of re- 

 sistant strains but may also lead to the 

 appearance of undesirable mutants of mi- 

 crobes. One should consider, further, the 

 dangerous potentialities of reduced natural 

 resistance in the human and animal body as 

 a result of the elimination of infectious or- 

 ganisms before the body has had a chance to 

 react immunologically. And finally, we must 

 not forget that antibiotics have contributed 

 many problems to geriatrics })y greatly in- 

 creasing the average life span of man. 



