Tetrazolium Reduction as a Means of DifferentiatingA Streptococcus faecalis from Streptococcus faecium

Abstract

SUMMARY: Tetrazolium (2:3:5-triphenyltetrazolium chloride) was used in a glucose nutrient medium to show the considerable differences in reducing properties between some of the Lancefield group D streptococci. The ability to reduce tetrazolium to formazan, in a glucose-containing medium, at an initial pH 6·0, distinguishes strains of Streptococcus faecalis from those of S. faecium (Orla-Jensen) which for many years have been classified in the same species as S. faecalis. Differences in reducing properties correspond with many other tests now used to separate these species. Measurements of the oxidation-reduction potentials in growing cultures showed that S. faecalis produced an Eh value about 150 mV. lower than S. faecium. Confirmation of the differences in reducing properties of these species was obtained by testing 68 freshly isolated strains of S. faecium and 34 strains of S. faecalis.