Dorothy Heilman

Mode of Action of Gramicidin

Conclusions 1. Gramicidin and tyrocidine depress the surface tension of aqueous solutions. Tyrocidine is more active in this regard than is gramicidin. 2. The ability of gramicidin to depress surface tension is improved by the addition of organic solvents such as glycerin which increases the solubility of gramicidin. 3. Serum decreases the activity of tyrocidine less than it does the activity of gramicidin, sodium oleate and aerosol OT. 4. The bactericidal and hemolytic effects of gramicidin are destroyed by heat but its property of altering surface tension is heat stable.

Hemolytic Effect of Gramicidin

Summary Gramicidin has a powerful hemolytic action against rabbits and sheeps erythrocytes in vitro. This activity is marked even in the presence of serum, plasma and tissue extract. The presence or absence of complement did not appear to affect the process.

Cytotoxicity of Streptomycin and Streptothricin

Summary Several different preparations of streptomycin were tested on cultures of rabbits spleen and were found to have a uniformly low toxicity for wandering cells and fibroblasts. Streptothricin had a relatively low cytotoxicity for leukocytes and macrophages but showed a fairly high cytotoxicity for fibroblasts.

Effect of Serum on Hemolysis by Gramicidin and Tyrocidine

Summary When gramicidin or tyrocidine in minimal effective amounts is added to suspensions of washed sheep erythrocytes, the rate of hemolysis is much more rapid with tyrocidine than with gramicidin but the latter, a!though slower in action, ultimately causes a greater degree of hemolysis than the former. Comparative experiments have been done to determine the influence of horse serum on the rate and amount of hemolysis caused by gramicidin and tyrocidine. The hemolytic activity of both substances is decreased in the presence of only 1% of horse serum. Five percent of serum causes further inhibition of the hemolytic activity of gramicidin and completely prevents hemolysis by tyrocidine. Increasing the amount of serum beyond 5% did not result in a further decrease of the hemolytic activity of gramicidin.