Lactobacilli represent a large group of bacteria found in decomposing plants and milk products. These rod-shaped microorganisms produce lactic acid from the breakdown of sugars like glucose, placing them in a broader category called lactic acid bacteria. Certain species are recognized for their role in food production and as members of the microbial communities in the human body.
Lactobacilli in the Human Body
Lactobacilli are inhabitants of several areas of the human body, particularly the digestive system and the female genital tract. These bacteria are considered commensal, meaning they benefit from living on the host. The host in turn provides a nutrient-rich environment for them to grow.
The primary function of lactobacilli in these areas is to maintain an acidic environment. In the vaginal microbiome, for example, these bacteria ferment glycogen to produce lactic acid, which lowers the pH to a range of 3.8 to 4.5. This acidity creates a protective barrier that discourages the growth of potentially harmful microorganisms.
The composition of lactobacilli can fluctuate based on various factors. For instance, in the vaginal tract, hormonal changes during a woman’s lifespan, particularly rising estrogen levels during puberty and pregnancy, support the growth of these bacteria. The gut can also serve as a reservoir for lactobacilli that may colonize the vaginal tract.
Lactobacilli in Foods and Fermentation
Lactobacilli are used to produce many fermented foods. They are used as starter cultures in manufacturing products like yogurt, cheese, sauerkraut, kimchi, and sourdough bread. This process is lactic acid fermentation, where they convert carbohydrates, such as sugars in milk or vegetables, into lactic acid.
The resulting lactic acid gives many fermented foods their characteristic tangy or sour taste. The acidic environment created by lactobacilli also acts as a natural preservative. By lowering the food’s pH, it inhibits the growth of spoilage-causing microbes, extending the product’s shelf-life.
Different species of lactobacilli contribute uniquely to the final product. In dairy fermentation, for instance, they break down milk proteins and fats, influencing the texture and aroma of cheese and yogurt. In sourdough bread, the bacteria produce both lactic and acetic acids, which, along with carbon dioxide from yeast, contribute to the bread’s flavor, chewy texture, and leavening.
Health Applications and Probiotics
Certain strains of lactobacilli are consumed for their health benefits as probiotics. Probiotics are live microorganisms that, when administered in adequate amounts, confer a health benefit on the host. They are taken as supplements, such as capsules or powders, or through fortified foods like yogurt.
Lactobacilli probiotics are primarily used for digestive health, where they help break down food and absorb nutrients. They can be useful for managing the symptoms of diarrhea, particularly when associated with antibiotics, by restoring the gut flora. They can also help with lactose digestion for individuals with intolerance.
Lactobacilli also help modulate the body’s immune system. They regulate inflammation and support immune responses against pathogens. In the vaginal tract, a microbiome dominated by lactobacilli is associated with lower levels of pro-inflammatory compounds and protection against infections. Oral probiotics with specific strains have been studied for their ability to colonize the vagina and reduce the recurrence of conditions like bacterial vaginosis.
The effects of lactobacilli are strain-specific. For example, Lactobacillus rhamnosus has been widely studied for its ability to support gut health and treat diarrhea. Meanwhile, Lactobacillus acidophilus is often associated with supporting vaginal health and assisting in lactose digestion.
Considerations and Side Effects
For most healthy individuals, consuming lactobacilli through food or supplements is safe. Side effects, when they occur, are mild and temporary. Common reactions include a short-term increase in gas, bloating, or constipation as the body adjusts.
Certain populations should exercise caution. Individuals who are critically ill or have a compromised immune system should consult a healthcare professional before taking probiotic supplements. In these groups, there is a rare risk of the probiotic bacteria causing an infection.
Antibiotics can reduce the effectiveness of lactobacilli probiotics, as they are designed to kill bacteria and may not distinguish between harmful and beneficial types. To avoid this interaction, it is recommended to take probiotic supplements at least two hours before or after taking an antibiotic.