A DIFFERENTIAL BROTH FOR SEPARATING THE LACTIC STREPTOCOCCI1

1 January 1971

journal article
Published by International Association for Food Protection in Journal of Milk and Food Technology

Vol. 34 (1) , 43-45
https://doi.org/10.4315/0022-2747-34.1.43

Abstract

Arginine degradation and citrate utilization, the major differentiating characteristics among lactic streptococci, formed the basis of a differential broth for separating Streptococcus cremoris, Streptococcus lactis, and Streptococcus diacetilactis strains in pure cultures. The medium contains milk as the sole source of carbohydrate (lactose), arginine and sodium citrate as specific substrates, and a suitable pH indicator (bromcresol purple), in addition to other ingredients. The pH of the medium is adjusted to 6.2 ± 0.05 (which becomes 6.15 ± 0.05 after sterilization) to increase citrate utilization and the broth is dispensed into test tubes containing Durham fermentation tubes. Streptococcus cremoris produces a yellow reaction (acid) in the broth. Streptococcus lactis initially turns the broth yellow, but on liberation of NH3 reverses the color back to the original violet hue. Streptococcus diacetilactis produces a violet reaction, and CO2 accumulates in the Durham fermentation tubes from the fermentation of sodium citrate.

Keywords

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