Observations on the Action of Streptomycin in vitro (I). ∗

Abstract

Summary

1. A standardized procedure for determination of sensitivity of microorganisms to streptomycin is described.

2. The sensitivity of an organism to streptomycin is influenced by age of culture, concentration of organisms, growth phase of culture, and constituents of medium used. Providing these factors are held constant, the sensitivity of a given strain will remain constant from day to day.

3. The action of streptomycin is bacterio-static rather than bactericidal. Its action is inhibited by certain growth stimulating substances such as peptone, as well as by certain reducing substances.

4. The sensitivity of 84 strains belonging to 7 species is described. Marked variation in sensitivity exists between different strains within a single species and at times between different cells within a given strain.

5. The sensitivity of 9 strains belonging to 8 species is essentially the same when tested against crude streptomycin sulfate (453 /xg/mg), against 3 preparations of the crys talline CaCl₂ double salt of streptomycin (685 to 708 /xg/mg) and against a preparation of streptomycin sulfate (802 /xg/mg) prepared from a crystalline salt.

6. The sensitivity of 4 strains of E. typhosa to certain preparations of impure streptomycin sulfate is greater than to highly purified streptomycin sulfate.