BACTERIOSTATIC AND BACTERICIDAL AGENTS 245 



Other Antibiotic Agents 



On comparing the action of citrinin with penicillic acid, the first was 

 found (698) to act largely upon gram-positive bacteria j the second, 

 like quinones, had a more widespread action, especially against the 

 colon-typhoid group. 



Considerable speculation has been focused upon the ability of vari- 

 ous organisms to inhibit the growth of M. tuberculosis. These comprise 

 various fungi, such as A. fumigatus (27, 870) and P. notatum (863), 

 bacteria, and a number of actinomycetes including species of Nocardia 

 and Streftomyces (831, 1029). The antibacterial action of some of 

 these organisms is believed to be due to the formation of substances 

 spoken of as tuberculocidins. The specific effects of some of the sub- 

 stances, which are now recognized, are described in detail elsewhere 

 (pp. 294-296). 



BACTERIOSTATIC AND BACTERICIDAL AGENTS 



Fleming (263) divided all selective bacteriostatic agents, exclusive 

 of the action of oxygen on anaerobic bacteria, into three groups: (a) 

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

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

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

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



Most of the antibiotics are characterized not only by their bacterio- 

 static action but also by marked bactericidal properties, the two usually 

 being parallel (963). Concentrations of an antibiotic substance smaller 

 than those needed to cause inhibition often stimulate the growth or 

 metabolic processes of the organism. In this respect these agents are 

 similar in action to synthetic detergents 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 (305). 



