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

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Abstract
2,3,5 Triphenyltetrazolium chloride (TTC) acted as an inhibitor of lactic acid production in 3 of 4 homo-fermentative lactic acid bacteria cultures studied. An increase in pyruvic acid and a decrease in lactic acid occurred when TTC was reduced by 3 of the 4 cultures. The concentration of TTC causing inhibition varied from 0.3 mg/ml for Streptococcus thermophilus to 0.8 - 1.0 mg/ml for Streptococcus lactis and Lactobacillus bulgaricus Streptococcus liquefaciens was not inhibited by TTC concentrations up to 1.4 mg/ml. This indicates a cell relatively impermeable to TTC or the possibility of an alternate metabolic pathway for lactic acid production by this organism. TTC reduction was inhibited by concentrations of iodo-acetic acid as low as 10-6 molar in some cultures.