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Observations on the Reduction of 2,3,5-Triphenyltetrazolium Chloride by Homofermentative Lactic Acid Bacteria¹

Department of Dairy and Food Industries and Department of Bacteriology, University of Wisconsin, Madison

ABSTRACT

Triphenyltetrazolium chloride (TTC) acted as an inhibitor of lactic acid production in three of four homofermentative lactic acid bacteria cultures studied. The concentration of TTC causing inhibition varied with the different cultures. An increase in pyruvic acid and a decrease in lactic acid occurred when TTC was reduced by three of the four cultures. Streptococcus liquefaciens also reduced TTC to a small extent, but was not inhibited by the TTC concentrations used. This indicates the possibility of a metabolic pathway for lactic acid production different from the other three organisms investigated, or a cell relatively impermeable to TTC. TTC reduction was inhibited by concentrations of iodo-acetic acid as low as 10^–6 molar in some cultures. These results indicate that the DPNH reduces the TTC to the formazan rather than reducing pyruvic acid to lactic acid, as normally occurs in glycolysis by homofermentative lactic cultures.

¹ Published with the approval of the Director of the Wisconsin Agricultural Experiment Station.

² Present address: Dairy Science Department, University of Florida, Gainesville, Florida.