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Lactobacillus acidophilus is one of several bacteria in the genus Lactobacillus. It is commonly used commercially together with Streptococcus salivarius in the production of yogurt.
Lactobacillus acidophilus gets its name from lacto- meaning milk, -bacillus meaning rod-like in shape, and acidophilus meaning acid-loving. This bacterium thrives in more acidic environments than most microorganisms (pH 4-5 or lower) and grow best at 45 degrees Celsius. L. acidophilus occurs naturally in a variety of foods, including dairy, grain, meat, and fish. It is also present in human (and animal) intestines, mouths, and vaginas. L. acidophilus (and all lactic acid bacteria) absorb lactose and metabolize it into lactic acid. Certain related species (known as heterofermentive) also produce ethanol, carbon dioxide, and acetic acid this way. L. acidophilus itself (a homofermentative microorganism) produces only lactic acid. Like many bacteria, L. acidophilus can be killed by excess heat, moisture, or direct sunlight.
In 2002, the complete genome of L. acidophilus was mapped and presented at the Seventh Symposium on Lactic Acid Bacteria in Egmond aan Zee, The Netherlands.
Health benefits
L. acidophilus is considered a probiotic or "friendly" bacterium. These types of healthy bacteria inhabit the intestines and vagina and protect against some unhealthy organisms. The breakdown of food by L. acidophilus produces lactic acid, hydrogen peroxide, and other byproducts that make the environment hostile for undesired organisms. L. acidophilus also tends to consume the nutrients many other microorganisms depend on, thus outcompeting possibly harmful bacteria in the digestive tract. During digestion, L. acidophilus also assists in the production of niacin, folic acid, and pyridoxine. Studies have also shown L. acidophilus can assist in bile deconjugation, separating amino acids from bile acids, which can then be recycled by the body.
Some research has indicated L. acidophilus may provide additional health benefits, including improved gastrointestinal function, a boosted immune system, and a decrease in the frequency of vaginal yeast infections. Some people report L. acidophilus provides relief from indigestion and diarrhea. A University of Nebraska study found that feed supplemented with L. acidophilus and fed to cattle resulted in a 61% reduction of Escherichia coli H7. Research at Oklahoma State University has indicated L. acidophilus may be helpful reducing serum cholesterol levels. Studies at the University of Kentucky indicated a treatment with L. acidophilus resulted in a 10 to 12% reduced risk of coronary heart disease in persons with high blood serum cholesterol levels.
L. acidophilus is part of the normal vaginal flora. The acid produced by L. acidophilus in the vagina helps to control the growth of the fungus Candida albicans, helping to prevent vaginal yeast infections. Certain spermicides and contraceptive creams can kill L. acidophilus in the vagina, clearing the path to possible yeast infections.
Antibiotics taken orally will also kill beneficial bacteria like L. acidophilus. After a course of antibiotic therapy, patients are occasionally instructed to take an L. acidophilus treatment in order to recolonize the gastrointestinal tract.
L. acidophilus is often sold in health stores in pill or powder form as a nutritional supplement. Research on the nutritional benefits of taking L. acidophilus supplements is inconsistent and inconclusive. Most such claims boil down to a link between L. acidophilus and a possible decrease in the incidence of certain diseases, including yeast infections, gastrointestinal disorders, and a weakened immune system. Most researchers agree further study is needed before substantiating many of these claims.
Food production
L. acidophilus can be used to make yogurt, sweet acidophilus milk, and other fermented dairy products. The bacteria produces lactate and acetate during fermentation. In yogurt production, L. acidophilus is added to milk to render it more acidic. The lactic acid it produces causes milk proteins to break down, coalescing into a more nearly solid gel substance - yogurt. By breaking down lactose to lactic acid, the bacteria make such dairy products digestable by lactose intolerant people. It can also be used to make "cultured soy" (commonly called soy yogurt) from soymilk in much the same way.
L. acidophilus can also be used to turn cabbage into sauerkraut, by converting sugars in the cabbage into lactic acid, which then acts as a preservative. Kimchi, a traditional Korean dish, is also fermented by L. acidophilus in this manner. Brined pickles are also manufactured through this process.
This family of bacteria is also responsible for producing some of the acids that give foods a sour taste. The distinct taste of Sourdough bread, for example, comes from L. acidophilus's cousin - Lactobacillus sanfranciscensis.
External links
- Bacteria Reduce Serum Cholesterol
- Deconjugation of bile acids by intestinal lactobacilli
- Friendly Bacteria - Lactobacillus acidophilus & Bifido bacterium
- Lactobacillus acidophilus, University of Nebraska, D.W. Brooks site
- Lactobacillus Genome Project
- Studies on L. acidophilus and L. bulgaricus, University of Kentucky
References
- Buttris, J. 1997. Nutritional properties of fermented milk products. International Journal of Dairy Technology 50(1):21-27
- Rasic JL: The Role of Dairy Foods Containing Bifido and Acidophilus in nutrition and Health. N European Dairy J 4:1-10 (1983)
- Salminen, S. and Von Wrigh, A., ed.1993. Lactic Acid Bacteria. Marcel Dekker Inc, NY
- Sandine WE: Roles of Lactobacillus in the Intestinal Tract. J Food Protection 42(3):259-62 (1979)
- Savaiano DA, et. al.: Lactose Malabsorption in Yogurt and Sweet Acidophilus Milk. Am J Clin Nutr 40(6):1219-20.
- Takahashi et al. 1993. BioScience-Biotechnology and Biochemistry. 57(9):1557-1560
- Tejuda et al. 1999. Effects of Lactobacillus spp. On cytokinan production of RAW 264.7 macrophage and El-4 thynoma cell lines. Journal of Food Protection.62(2);162-169
- Vela, G. 1997. Applied Food Microbiology. Star, CA
- Wardlow, G.M. 1999. Perspectives in Nutrition. Mcbraw-Hill, Boston
- Wood, B.J, ed. 1992. The lactic acid bacteria in health and disease. El Sevier Appied Science, London
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"Lactobacillus acidophilus"