194 



NATURE OF ANTIBIOTIC ACTION 



plete inhibition with no multiplication and no deaths. A further increase 

 in the concentration of disinfectant results in the death of some organ- 

 isms per unit of time, and eventually a concentration is reached at which 

 all organisms die rapidly (Figure 20). Any rate of multiplication 



Figure 20. Disinfectant spectrum and rates of bacterial growth. From Mar- 

 shall and Hrenoff (584). 



greater than zero but less than normal can be considered as the bacterio- 

 static zone, and the rate less than zero as the bactericidal zone. Accord- 

 ing to this concept of bacteriostasis, bacterial growth may be delayed 

 under the influence 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 (189): the acidic and basic properties of the bac- 

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



