Dihydrostreptomycin accumulation in E. coli

Abstract

DIHYDROSTREPTOMYCIN is an antibiotic composed of streptidine, dihydrostreptose and N-methyl-L-glucosamine joined by two glycosidic bonds. It differs from streptomycin only in that the aldehyde group on the middle residue (streptose) is reduced. Both compounds have similar biological actions^1,2 but their accumulation by bacterial cells has been little studied. Passive diffusion is often assumed to be responsible, although Mitchell thought it improbable that a molecule such as streptomycin passes through a lipid layer³. Anand et al. proposed a mechanism in two phases⁴. First, a small amount of antibiotic would enter by passive diffusion regardless of an intact lipid layer and affect protein synthesis so as to cause deterioration of membrane integrity. Then more rapid accumulation would follow by passive diffusion through the disrupted lipid barrier. Alternatively, Hurwitz et al. showed streptomycin accumulation to be sensitive to chloramphenicol during initial exposure and insensitive after several minutes of exposure. They suggested facilitated diffusion, with entry of the antibiotic depending on a streptomycin-induced protein⁵.