CHAPTER I I 



THE NATURE OF ANTIBIOTIC ACTION 



Sulfanilamide, -penicillin, and gramicidin can be clearly set afart 

 from, the classical antiseptics which are general protoplasmic 

 poisons. All three substances are primarily bacteriostatic rather 

 than bactericidal in their action. Since they do not destroy the res- 

 piration of bacteria, one may assume that the inhibition of growth 

 which they cause depends not upon interruption of the celltdar 

 metabolism as a whole, but rather upon some subtle interference 

 with certain individual reactions. To interrupt the pathogenic 

 career of an infectious agent, therefore, it is not necessary to kill 

 the invading cell, but only to block one step in its metabolic path 

 by some specific inhibitor. — Dubos. 



ANTIBIOTIC SUBSTANCES AND CHEMICAL 

 DISINFECTANTS 



Since antibiotic substances vary greatly in their origin and in their 

 chemical nature, they may be expected to vary also in their mode of 

 action upon the cells of bacteria and other microorganisms, and in the 

 effect upon the animal tissues when these agents are used for chemo- 

 therapeutic purposes. Comparatively little is known concerning these 

 mechanisms. It is known, however, that antibiotic substances act chiefly 

 by interfering with the growth of the bacterial cell, although in many 

 cases they are able to bring about the lysis of the cell as well. Because 

 of the first effect, it has been assumed that antibacterial agents are struc- 

 turally related to bacterial metabolites that usually function as co- 

 enzymes (600). In this connection, the following properties of anti- 

 biotic agents are of particular significance: 



Most antibiotics are strongly bacteriostatic and only weakly bactericidal, 

 though a few are also strongly bactericidal and some are even bac- 

 teriolytic. 



Some substances act primarily in vitro and only to a limited extent in vivo 

 because of interference of the body tissues with their action; others, 

 however, act readily upon bacteria in vivo. 



