222 



NATURE OF ANTIBIOTIC ACTION 



DISINFECTANT "SPECTRUM- 



impractical 

 (insoluble, 

 too toxic. 



OR ) 



100% 



GENTIAN VIOLET 



Space about 1/20 to-tol length 



Spoce just perceptible (.001%) 



Figure 21. Disinfectant spectrum. From Marshall and Hrenoff (621). 



the rate less than zero as the bactericidal zone. According to this con- 

 cept of bacteriostasis, bacterial growth may be delayed under the influ- 

 ence of a disinfectant for many days or for many hours j or the bacteria 

 may progressively die over a period of many days. 



The following factors influence the selective action of an antibiotic 

 agent upon bacteria (200): the acidic and basic properties of the bac- 

 terial cell, the nature and property of its membrane, its permeability, 

 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- 



