ANTIBIOTIC SUBSTANCES AND DISINFECTANTS 195 



the relative importance for metabolism and viability of the specific bio- 

 chemical systems affected by the agent, the activity of autolytic enzymes 

 in the bacterial cell, as well as others. 



Marked differences exist in the degree of sensitivity of various bac- 

 teria to different antibiotic substances and chemical agents. Gramicidin 

 is most specific in its action, being limited to the cocci and acting upon 

 actinomycetes to only a limited extent. Penicillin is next in its selective 

 action. Actinomycin, tyrocidine, and gliotoxin act primarily upon the 

 gram-positive organisms and actinomycetes, and much less upon gram- 

 negative bacteria. The selective action is in contrast to the generalized, 

 even if more limited, action of phenol and quinone, which act alike on 

 both gram-positive and gram-negative organisms. Pyocyanase, pyo- 

 cyanin, and the culture filtrate of P. notatum (due to the presence of 

 notatin) are similar in some respects but not in others to the chemical 

 compound in their action j they are found to be generally bacteriostatic 

 over a wide range of test organisms, no sharp division being obtained 

 upon the basis of the gram stain, Streptothricin is unique in its action j 

 the gram-positive spore-former B. suht'd'is is most sensitive, but the 

 other spore-former B. mycoides is not affected at all. The gram-negative 

 E. colt is more sensitive to streptothricin than either M. lysodeiktkus 

 or S. lutea. Sulfanilamide has a definite, even if limited, retarding effect 

 upon the growth of various organisms. The antibiotic substances of 

 microbial origin are generally found to be stronger bacteriostatic agents 

 than the chemicals tested. A high bacteriostatic effect is not necessarily 

 accompanied by a correspondingly high bactericidal action. Gliotoxin, 

 one of the most active bacteriostatic substances among those tested, pos- 

 sesses lower bactericidal properties than other preparations. Strepto- 

 thricin, on the other hand, is highly bacteriostatic and bactericidal 

 against certain gram-negative bacteria. 



The specific morphological differences among the bacteria, based 

 upon the gram stain (205), as shown by their sensitivity toward anti- 

 biotic substances, are thus found to be relative rather than absolute. 

 Most of the gram-positive bacteria are more sensitive to the majority 

 of antibiotic substances than are the gram-negative bacteria. But other 

 an,tibiotic agents, such as streptothricin, streptomycin, and clavacin, act 

 quite differently and show marked variations within each group. 



