Some results of the tetrazolium reduction test to differentiate Lancefield Group D streptococci

Abstract

Because of the easy visual assessment, the number of equivocal results was reduced in the tetrazolium reduction test for distinguishing between Str. faecalis and Str. faecium by using a stab inoculation method instead of surface sowing or growth in liquid.
AU 12 strains designated Str. faecalis by other workers were positive by the stab method, whereas one was negative by both broth and plate techniques. Fifteen of 16 strains of Str. faecium were negative by the stab method, 12 by plate method and 15 by broth method. One of 3 strains of Str. durans was positive by all methods and 2 were negative by all methods. All 5 strains of Str. bovis were positive by the stab method and 4 were negative by both broth and plate methods.
Twenty of 31 Queensland strains of Str. faecalis were positive by all methods, 2 by broth and plate but not stab, 2 by stab only, and 7 were negative by all methods. One of 35 Queensland strains of Str. f aecium was positive by all methods, 3 were positive by broth and plate but not stab, 6 were negative by broth and plate but positive by stab method, and 27 were negative by all methods.