BACTERIOSTATIC AND BACTERICIDAL AGENTS 



209 



physiological agents, including bile, serum, proteolytic enzymes, and 

 lysozymej (b) microbiological products, comprising the antibiotic sub- 

 stances} (c) chemicals of known composition, including dyes, salts (po- 

 tassium, tellurite, mercuric salts), and other agents. 



Concentrations of antibiotic substance smaller than those needed to 

 cause inhibition often stimulate growth of the organisms or of their 

 metabolic processes (705). In this respect these agents are similar in 

 their action to synthetic detergents (35) and to other chemical disin- 

 fectants, as discussed previously. It may also be of interest to note here 

 that the antibacterial action of straight-chain mono-amines and di- 

 amines, amidines, guanidines, and quaternary bases increases with the 

 length of the chain up to a maximum and then decreases, the gram- 

 positive bacteria being more sensitive than the gram-negative organ- 

 isms. Serum increases the activity of the shorter-chain compounds and 

 decreases that of the longer-chain compounds, depending to a consider- 

 able extent upon the test bacteria (303). 



The bactericidal action of antibiotic agents, as influenced by their 

 concentration, can be illustrated by the action of pyocyanase (Table 39). 

 In a study of the bactericidal action of actinomycin (946) it was 

 found that the addition of 0.5 mg. of actinomycin to a 10 ml. sus- 

 pension of E. coli reduced the number of viable cells from 6,400,000 

 to 493,000, the methylene blue reduction test remaining positive j 

 I mg. actinomycin reduced the number of cells to 4,800, the reduction 

 test becoming negative j 2 mg. of the agent brought about complete de- 



TABLE 39. BACTERICIDAL ACTION OF PYOCYANASE UPON THREE BACTERIA 



From Emmerich, Low, and Korschun (237). 



