190 NATURE OF ANTIBIOTIC ACTION 



A few antibiotic agents are fairly nontoxic to the animal body; others are 

 somewhat more toxic but can still be utilized; and some are so highly 

 toxic that they offer little promise as chemotherapeutic agents. 



Antibiotic agents differ greatly in their solubility: some are water soluble; 

 others are alcohol soluble and only slightly soluble in water; and 

 some are acids and react with alkali solution to form soluble salts. 



Some antibiotic agents are stable under a variety of conditions, whereas 

 others are unstable. 



Some antibacterial substances are hemolytic; others have apparently no 

 injurious effect upon the blood cells. The latter can, therefore, be 

 used for general body treatment, whereas the former are suitable 

 only for local applications. 



Since antibiotic substances are selective in their action upon microorgan- 

 isms, none can be expected to be utilized as general agents against all 

 bacteria. This also points to the remarkable physiological differences 

 in the morphology and physiology of the bacterial cells, and to the 

 differences in the mode of action of the different antibiotic substances 

 upon the various bacteria. 



A comparison of the antibacterial action of the antibiotic substances 

 produced by two bacteria v^^ili serve to illustrate some of the foregoing 

 points. Pyocyanin, produced by Ps. aeruginosa, inhibits the growth of 

 many gram-positive and gram-negative bacteria in dilutions as high as 

 1 : 1 00,000 J pyocyanase and hemipyocyanin have less activity upon the 

 bacteria, but yeasts are more sensitive to them than to pyocyanin. Ty- 

 rothricin, produced by B. hrev'ts, is far more specific in its action, which 

 is limited largely to gram-positive bacteria. The sensitivity of patho- 

 genic fungi to these compounds also differs markedly (855). Other 

 striking differences are found on comparing two types of antibiotic sub- 

 stances produced by fungi, namely, penicillin and clavacin, and two 

 substances produced by actinomycetes, namely, streptothricin and ac- 

 tinomycin. The bacteriostatic spectra of these four substances are re- 

 corded in Table 35. The first of each pair has a limited toxicity to ani- 

 mals, and the second is highly toxic. Whereas penicillin acts largely 

 upon gram-positive bacteria and only upon a few gram-negative organ- 

 isms, streptothricin acts alike upon certain bacteria within each group. 

 Clavacin and actinomycin, both of which are highly toxic, differ simi- 

 larly in their action upon bacteria, the first being largely active against 



