216 NATURE OF ANTIBIOTIC ACTION 



cal modifications. Aside from cell proliferation, the important meta- 

 bolic processes commonly considered to be affected by antibiotic agents 

 were oxygen uptake, acid production, and dehydrogenase activity. Some 

 agents apparently can inhibit cell growth without destroying the viabil- 

 ity of the cells and their capacity for taking up oxygen. 



Gramicidin and tyrocidine were believed to affect bacteria (390, 391, 

 579) by depressing the surface tension of aqueous solutions. This effect 

 was favored by the addition of organic solvents such as glycerin, which 

 increases the solubility of gramicidin. The addition of serum resulted 

 in a decrease in activity of tyrocidine, to a less extent, however, than of 

 gramicidin. Heat destroyed the bacterial and hemolytic effects of 

 gramicidin, but the property of altering surface tension was heat-stable. 

 It has further been shown (395) that gramicidin, after an initial stimu- 

 lation, inhibited oxygen consumption of bovine spermatozoa and ren- 

 dered them immobile J aerobic as well as anaerobic glycolysis was de- 

 pressed by about 40 per cent and motility of the spermatozoa impaired. 

 Tyrocidine, however, caused a small reduction in the oxygen consump- 

 tion and in glycolysis. The action of gramicidin upon the metabolic ac- 

 tivities of S. aureus and S. hemolyticus was shown (206) to be influ- 

 enced by the composition of the medium, the presence of potassium and 

 phosphate ions giving a prolonged stimulation of metabolism, whereas 

 ammonium ions favored a depression in oxygen uptake. 



The specific effects of basic proteins, such as protamine and histone, 

 upon the activity of selective inhibitors offered a possible explanation 

 for the difference in the action of tyrothricin upon gram-positive and 

 gram-negative bacteria (606). These basic proteins also possess antibac- 

 terial properties. They have the capacity of sensitizing gram-negative 

 bacteria by means of substances which otherwise act only on gram- 

 positive forms. This is brought out in Figure 28. 



Pneumococci grown in media containing the specific enzymes which 

 hydrolyze their capsular material are deprived of these capsules and 

 fail to agglutinate in the specific antiserum. The enzymes do not inter- 

 fere with the metabolic functions of the cells, but their action is directed 

 essentially against the capsule (193). These enzymes were found not 

 only to exhibit great selectivity but to be highly specific against the 

 particular polysaccharides. 



