Inhibitory Action of Selenite on Escherichia coli, Proteus vulgaris , and Salmonella thompson

Abstract

The resistance of three microorganisms, E coli (ISU-41), P vulgaris (ISU-37c), and S thompson (ISU-86-2), to increasing concentrations of selenite was determined: E coli was completely inhibited by 1.25% sodium hydrogen selenite, and 0.25% sodium hydrogen selenite caused a pronounced lag; P vulgaris survived selenite concentrations of over 3%; S thompson was inhibited completely by 3% selenite but not by 2.5%, although there was a considerable lag and a decrease in total growth. The relationship of growth, uptake, and reduction of selenite was determined. The susceptible E coli incorporated up to twice as much selenium as did the other two organisms during the early stages of incubation. Radio-autographs of seleno analogues of sulfur-containing amino-acids revealed the presence of selenocystine in all three organisms, and seleno-methionine in E coli. Compounds having Rf values corresponding to possible oxidation products of seleno-methionine were present in the hydrolysates of P vulgaris and S thompson. Kinetic aspects of selenite uptake, rather than the ultimate localization of selenite in the cell protein, appear to be the factors that determine the degree of resistance or of susceptibility to selenite.