Influence of Certain Substances on Activity of Streptomycin. I. Modifications in Test Medium

Abstract

Under standard test conditions, raising the conc, of tryptone from 0.50% to 1.0%, in a medium containing only tryptone and water, raised the minimum inhibiting conc, of streptomycin for Klebsiella pneumoniae (A.T.C.C. 9997) from 0.036 units per ml. to 0.084 units per ml. Further addition of glucose to the medium increased the minimum inhibiting conc, to a lesser, but, nevertheless, definite degree. This latter effect is due in part to lowering of the pH of the test broth on autoclaving when dextrose is present. The minimum inhibiting conc, of streptomycin in an enriched broth containing Na glycolate was about 10 times greater than in 0.75% tryptone. Substitution of Na thioglycolate for Na glycolate further greatly increased the minimum inhibiting conc, of streptomycin. This additional interference by Na thioglycolate was observed to decrease as the broth aged (and hence as the thioglycolate was oxidized). Since thioglycolate per se has been said to cause no significant destruction of streptomycin, it is proposed that its interfering action may be due to its role in reducing the oxidation-reduction potential of the medium and that perhaps streptomycin interferes more with aerobic than anaerobic metabolism of the test organism.