Like many probiotic strains, Lactococcus lactis has been used for hundreds of years to ferment foods such as cheese, yoghurt, sauerkraut. It works by fermenting milk sugar (lactose) into lactic acid, which makes it a useful tool in the cheese-making industry. Lactococci are non motile, non-spore forming bacterium that are usually associated with plant material (mostly grasses). This bacterium is easily inoculated into milk.
Although Lactococcus lactis is related to other lactic acid bacteria (such as Lactobacillus acidophilus) that colonize the intestines and mouth, L. lactis doesn’t usually colonize human tissues. It also differs from other lactic acid bacteria in terms of its pH, salt, and temperature tolerances for growth.
Besides the production of fermented dairy products, Lactococcus lactis is now being utlitized for biotechnological applications in genetic engineering for the production of various recombinant proteins and metabolites, particulary in vaccine delivery systems. In recent years, scientists have developed a means of using L. lactis for nisin-controlled gene expression (NICE).
However, Lactococcus has one very important feature: it’s a component of nisin, an antibiotic-like substance that fights a wide variety of Gram-positive bacteria. This includes food-borne pathogens such as Listeria, Staphylococcus and Clostridium. Research suggest that nisin targets the cell membrane of these bacteria.
Nisin is a natural preservative present in cheese made with Lactococcus lactis ssp. lactis, but can also be used as a preservative in foods with low pH. Because nisin cannot be synthesized chemically, Lactococcus lactis strains are commonly used for this purpose.
For humans, the most important use of Lactococcus lactis is in boosting the immune system. L. lactis has been shown to be particularly effective in delivering antigens that stimulate mucosal immunity to pathogens of the respiratory tract. It also appears to to exhibit protection against nonrespiratory pathogens, such as HIV, Human papilloma virus and the malarial parasite.
Because L. lactis can survive the harsh conditions of the gastrointestinal tract but doesn’t colonize the gut (like other Lactobacillus strains), it can be used as a “vehicle” to deliver therapeutics such as cytokines into the human body. This was first done in a study involving mice with colitis, where engineered secretion of interleukin-10 (IL-10) in L. lactis was used to treat inflammatory bowel disease.
A Japanese study has also found health benefits for Lactoccocus lactis. By using the bacteria Salmonella Flagellar, researchers were able to use L. lactis to produce acetate (through lactose fermentation) and subsequently interrupt the rotation of the bacteria’s flagella – thus hindering the ability of the Salmonella to move through the body. It was concluded that Lac. lactis may be a useful tool for preventing infections by multiple bacterial species.