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Carbohydbate Metabolism of Lactic Acid Cultures.^1,2, I. Effects of Antibiotics on the Glucose, Galactose, and Lactose Metabolism of Streptococcus Lactis

Department of Dairy Husbandry, University of Nebraska, Lincoln

ABSTRACT

Streptococcus lactis UN metabolized glucose, galactose, and lactose and produced varying amounts of lactic, formic and acetic acids, carbon dioxide, ethanol, and glycerol. Lactic acid constituted the major product, accounting for 26 to 93% of the metabolized sugar. Possible mechanisms of production of the various metabolites are discussed. Under the conditions of the study, S. lactis, normally a homofermenter, functioned as a heterofermenter. The results indicate that the organism metabolized the sugars partly through classical glycolysis and partly through the hexosemonophosphate shunt pathway.

Penicillin and streptomycin inhibited almost completely the growth of the organism, the utilization of carbohydrates, and the production of various metabolites for the first 18 to 24 hr. However, upon extended incubation up to 48 hr, the organism grew, metabolized sugars, and produced acid and the various metabolites. In general, in the presence of the residual antibiotics, the emerging cells produced lactic acid and carbon dioxide at a reduced rate. Penicillin was more inhibitory toward the fermentation of the monosaccharides than toward that of the disaccharide, and the reverse was true for streptomycin. Aureomycin and terramycin inhibited completely the growth, the sugar metabolism, and the acid production up to 48 hr of incubation.

¹ Supported by a grant from the U. S. Public Health Services (National Institutes of Health).

² Published with the approval of the Director as paper no. 1240, Journal Series, Nebraska Agricultural Experiment Station, Lincoln.