Lysine Lactose Broth

Lysine Lactose Broth is used for determination of lysine decarboxylase activity of lactose non-fermenting members of Enterobacteriaceae, especially Salmonellae. Dextrose and lactose are the fermentable sugars. L-Lysine is the substrate that is decarboxylated due to decarboxylase enzyme activity. Bromocresol purple acts as the pH indicator. The enteric bacilli produce acid in an initial fermentation (lactose). Lactose non-fermenters produce acid from dextrose resulting in the formation of yellow colour. Subsequently L-Lysine is decarboxylated to form cadaverine resulting in an alkaline reaction and the broth reverts to purple colour.