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Detection by Warburg manometry of compounds stimulatory to lactic acid bacteria

SUMMARY The effect of aqueous algal extract, yeast extract casein peptone and meat peptone on acid production by 4 strains of lactic acid bacteria was tested manometrically using a milk–bicarbonate medium. A strain-dependent stimulation of the bacteria was detected after 4 h incubation. After fractionation of an aqueous extract of the green alga Scenedesmus obliquus on a Sephadex G25 column, 2 fractions with stimulatory activity were found using Streptococcus lactis as the test organism. One of the peaks of activity, confined to shortening of the lag phase, was due to hypoxanthine which, however, had only a slight stimulatory effect in conventional milk souring tests. The manometric method provides a sensitive and rapid test for detecting compounds with biological activity in µg amounts, but it should be accompanied by milk souring tests for interpretation of the type of stimulation involved.