ANTIMICROBIAL AND ANTITUMOR ACTIVITIES 



87 



GLIOTOXm 



8 12 16 20 24 



CONCENTRATION OF ANTIBIOTIC, M/iG/ML 



32 



Figure 3. Eft'oct of ;intil)iotics on the multiplication of L cells of mouse tihrohlasts. (Reproducec 

 from Perlman ct <d. Proc. Soc. Exptl. Biol. Med. 102: 290-292, 1959.) 



toxin production in Staph, aureus l)y clilor- 

 aniphenieol, the tetracyclines, and oleando- 

 mycin i.^ directly proportional to inhibition 

 of growth. Streptomycin and bacitracin in- 

 hilMt toxin production to a degree out of 

 proportion to growth inhibition. 



Chemical Structure and Antibiotic 

 Activities 



The marked variations in the antimicro- 

 l)ial activities of the antibiotics, or their 

 antimicrobial spectra, present a type of 

 problem that defies any attempt at logical 

 speculation on the possible relation between 

 chemical structure and biological activity. 

 Some antibiotics possess a wide or l)road 

 spectrum of antimicrobial activity; others 

 are characterized by a very narrow spectrum 

 of activity. 



The following questions logically present 

 themselves in this connection: 



Why do some antibiotics act upon bac- 

 teria alone, others on fungi alone, and still 

 others upon both luicteria and fmigi? Why 



do some affect the rickettsiae anfl the other 

 intracellular parasites and not th(^ true 

 viruses? 



Why ai-e the gram-positive bacteria far 

 more sensiti\'e to the great majority of 

 antibiotics produced by a<'t inomycetes than 

 are the gram-negative bacteria? 



Why do some antibiotics have a marked 

 acti\-ity u])on acid-fast l)acteria, whereas 

 others, e\en though active upon various 

 gram-positive bacteria, have no effect? 



Why do certain closely related groups of 

 bacteria, such as those found among the 

 aerobic spore-formers (B. subtilis versus B. 

 mijcoides) or among the gram-negati\-e bac- 

 teria {E. coli versus A. aerogenes), often differ 

 greatly in their sensitivity to certain anti- 

 biotics? 



Why are some antibiotics active only 

 upon gram-positi\'e bacteria and not upon 

 gram-negati\'e forms, whereas some are ac- 

 tive on both gram-posit i\'e and gram-nega- 

 tive bacteria? 



Whv do some l)acteria and not others 



