Lactobacillus casei is recognized as a beneficial bacterium that belongs to the group of microorganisms known as Lactic Acid Bacteria (LAB). This organism is widely studied for its ability to survive the harsh conditions of the human digestive tract, allowing it to temporarily establish itself in the gut and interact with the host’s intestinal system. The bacterium is frequently utilized in the food industry and in dietary supplements. Its application is rooted in its natural biological properties and its capacity to contribute to the balance of the gut environment.
Classification and Natural Habitat
Lactobacillus casei is a Gram-positive, non-spore-forming, rod-shaped bacterium classified as a facultative anaerobe, meaning it can survive with or without oxygen. While historically known as Lactobacillus, it has recently been reclassified into the genus Lacticaseibacillus, placing it within the larger family of lactic acid bacteria.
The organism’s main metabolic process is homofermentation, converting glucose and other carbohydrates primarily into lactic acid, accounting for at least 85% of its end products. This acid production is a defining trait of the species and helps preserve fermented foods. L. casei is a highly adaptable species that naturally exists in diverse environments.
Its natural habitats include the human mouth and the entire gastrointestinal tract. It is also present in fermented foods like dairy products (such as cheese and cultured milk) and fermented plant materials (including olives and pickles). The bacterium’s environmental flexibility and acid tolerance allow it to thrive in both fermented products and the digestive system.
Specific Contributions to Gut Health
L. casei’s ability to survive the journey through the stomach and small intestine is a prerequisite for its beneficial actions. Many strains tolerate the low pH of gastric acid and the presence of bile salts. This resilience allows the bacterium to reach the lower intestine alive, where it interacts with the resident microbiota and the intestinal lining.
One primary mechanism by which L. casei supports the gut environment is competitive exclusion against harmful microorganisms. This involves competition for adhesion sites on the intestinal wall and for limited nutrients. Furthermore, it produces antimicrobial substances, such as organic acids and bacteriocins, that inhibit the growth of certain pathogens.
L. casei also supports the structural integrity of the intestinal barrier, which is made up of a layer of epithelial cells sealed by tight junction proteins. Specific strains can positively influence the expression of these tight junction proteins, which helps to reduce intestinal permeability. This strengthening of the physical barrier prevents the passage of unwanted substances from the gut lumen into the bloodstream.
The bacterium interacts with the host’s immune system, often by engaging with gut-associated lymphoid tissue (GALT). Studies show that L. casei can modulate immune cell activity, including increasing the number of IgA-producing cells. By regulating signaling molecules, L. casei promotes a balanced immune response, activating certain cells while helping to control excessive inflammatory reactions.
Certain strains also contribute to the digestion of complex carbohydrates, such as oligosaccharides, which humans cannot fully break down. This fermentation process can lead to a reduction in intestinal gas and flatulence, as the bacterium processes these compounds.
Integration into Food and Supplements
The commercial application of L. casei stems from its natural ability to ferment sugars. It is widely used in the industrial production of various fermented dairy products, including specific types of cheese and cultured milks. The fermentation contributes to the characteristic flavor and texture of these products, and acts as a natural preservative due to the lowering of pH.
Due to its documented health-supporting properties, L. casei is also included in functional foods and dietary supplements. It is often incorporated into yogurts, specialized dairy beverages, and non-dairy probiotic formulations. The bacterium’s natural tolerance to acidic conditions makes it a suitable candidate for commercial products, enhancing its stability and shelf life.
The safety of L. casei for human consumption is well-established. Multiple strains have been granted the Generally Recognized As Safe (GRAS) status by regulatory bodies, confirming that the bacterium is considered safe for inclusion in the food supply when used under intended conditions.