Microbiological Media Supplementation: Added to culture media as a carbohydrate source; 20% Lactose Solution is commonly used to prepare lactose-containing broths and agars.

Selective/Differential Media Preparation: Used to formulate media like MacConkey and EMB to differentiate lactose fermenters (e.g., Escherichia coli, Klebsiella) from non-fermenters (e.g., Salmonella, Shigella).

Coliform and Water/Food Testing: Supplement for Lactose Broth and related media; 20% Lactose Solution supports detection of coliforms via acid/gas production.

Biochemical Fermentation Tests: Used in phenol red lactose broth and Durham tube assays to assess lactose fermentation profiles of bacteria.

Carbon Source in Minimal Media: Provides lactose in M9 or other defined media to select for lac+ strains and study metabolism in Escherichia coli.

Lac Operon Induction/Autoinduction: Serves as a natural inducer of lac-based expression systems and for autoinduction of T7/lac promoters in recombinant Escherichia coli.

Beta-Galactosidase Studies: Used alongside reporter assays (e.g., ONPG/MUG) to modulate lac expression levels for measuring β-gal activity.

Cultivation of Lactic Acid Bacteria: Provides a fermentable sugar for dairy-associated organisms such as Lactobacillus spp. and Streptococcus thermophilus.