Lactococcus lactis

Lactococcus lactis is a species of non-sporulating, non-motile, Gram-positive bacteria used extensively in the production of buttermilk and cheese. L. lactis are cocci that group in pairs and short chains, typically 0.5 - 1.5 µm in length. When fermenting milk, L. lactis produce large quantities of lactic acid. Cultured in the laboratory, L. lactis colonies appear bright orange on nutrient agar.

Cheese production
L. lactis subsp. lactis (formerly Streptococcus lactis ) is used in the early stages for the production of many cheeses including Brie, Camembert cheese, cheddar, Colby, Gruyère, Parmesan, and Roquefort.

The use of L. lactis in dairy factories is not without issues. Bacteriophages specific to L. lactis cause significant economic losses each year by preventing the bacteria from fully metabolizing the milk substrate. Several epidemiologic studies showed that the phages mainly responsible for these losses are from the species 936, c2 and P335.