In vitro Observations of the Mode of Action of Streptomycin. ∗

Summary

1. Streptomycin in bacteriostatic concentrations produced morphological changes in some Gram-negative bacilli but not in others. Gram-positive cocci were only slightly affected, and Gram-positive bacilli were not affected, 2. Streptomycin was bactericidal for E. coli in the resting state, the effect being related both to the size of the inoculum and the concentration of the antibiotic. 3. Strains of E. coli resistant to streptomycin under conditions, permitting growth were also resistant in the resting state, but exposure of susceptible strains to streptomycin in the resting state did not result in increased resistance. 4. No stimulation of the rate of growth of K. pneumoniae was observed in vitro by subinhibitory concentrations of streptomycin.