Indirect Conductance for Measurements of Carbon Dioxide Produced by Streptococcus salivarius ssp. thermophilus TJ 160 in Pure and Mixed Cultures

The C02 produced by Streptococcus salivarius ssp. thermophilus TJ 160 during urea hydrolysis was estimated using indirect conductance measurements in pure culture and in mixed cultures with Lactobacillus. To quantify the concentration and rate of C~production, conductance measurements were converted to C02 values; -240 pS corresponded to 1 /lmol of C02 at 37C. The estimation of C02 produced by S. salivarius ssp. thermophilus in reconstituted skim milk was related to the amounts of urea degraded in pure and mixed cultures. Lactobacil- lus delbrueckii ssp. bulgaricus and Lactobacillus acidophilus did not consume urea or produce C02. Part of the C02 produced by S. salivarius ssp. thermophilus disappeared during growth in mixed cultures with Lactobacillus.