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Lactobacillus is the name given to a group of Gram-negative bacteria that do not form spores but derive energy from the conversion of the sugar glucose into another sugar known as lactose. The name of the genus derives from the distinctive sugar use. Lactobacillus has a number of commercial uses, especially in aspects of dairy production, including the manufacture of yogurt. As well, Lactobacillus is part of the normal microbial population of the human adult vagina, where it exerts a protective effect.

Prominent examples of the genus include Lactobacillus acidophilus, Lactobacillus GG, Bifidobacterium bifidum, and Bifidobacterium longum.

A distinctive feature of the members of the genus Lactobacillus is the formation of lactic acid from glucose. This is the property that confers the sour taste to natural, Lactobacillus -containing yogurt. As well, the lactic acid lowers the pH of the environment that the bacteria dwell in. In the case of the vagina, this acidic change can inhibit the growth of other, harmful invading bacteria. Consistent with this, the use of suppositories containing Lactobacillus species has been successful in controlling recurrent bacterial vaginal infections. Similarly, use of the bacterium has been promising in the control and prevention of recurrent urinary tract infections.

Aside from the exclusion of bacteria due to the pH alteration in the vagina or urinary tract, Lactobacillus also adheres to cells lining the vagina and the urinary tract, and colonizes these surfaces. The luxuriant growth of these bacteria excludes other bacteria from gaining a foothold. This phenomenon is known as competitive exclusion.

Commercially, Lactobacillus is best known as the basis of yogurt manufacture. A mixture of Lactobacillus bulgaricus or Lactobacillus acidophilus and Streptococcus thermophilus produce the lactic acid that ferments milk.

Yogurt that contains live bacteria usually contains Lactobacillus acidophilus. There is evidence that the persistence of the bacteria in the intestinal tract for up to a week after consuming yogurt increases the number of antibody-secreting cells in the intestine. Also Lactobacillus acidophilus bacteria possess and enzyme called lactase that enables the bacteria are to utilize undigested starches, particularly those in milk, that would otherwise be eliminated from the body.

Yet another benefit of Lactobacillus is the production of beneficial compounds that are used by the body. For example, Lactobacillus acidophilus produces niacin, folic acid, and pyridoxine, a group of compounds that collectively are referred to as the B vitamins.

Another noteworthy strain of Lactobacillus is known as Lactobacillus GG. This strain was isolated from humans in the 1980s by Drs. Sherwood Gorbach and Barry Goldin. The initials of their last names are the basis for the GG designation. Lactobacillus GG has shown great promise as a nutritional supplement because the bacteria are able to survive the passage through the very acidic conditions of the stomach. They then colonize the intestinal tract. There, the bacteria produce a compound that has antibacterial activity. This may help maintain the intestinal tract free from invading bacteria.

See also Microbial flora of the stomach and gastrointestinal tract; Probiotics

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Lactobacillus A genus of Gram-positive bacteria in which the cells are ovoid or rod-shaped; most are non-motile. They are chemo-organotrophic, have complex nutritional requirements, and are found in various habitats where carbohydrates are available as nutrients. They rarely cause disease. Some strains are used in the manufacture of certain dairy products, e.g. yoghurt and cheese.

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Lactobacillus (lak-toh-bă-sil-ŭs) n. a genus of Gram-positive nonmotile rodlike bacteria that are capable of producing lactic acid from the fermentation of carbohydrates. They are found in fermenting animal and plant products, especially dairy products, and in the alimentary tract and vagina.

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lactobacillus (pl. lactobacilli) Any one of a group of rod-shaped Gram-positive anaerobic bacteria of the genus Lactobacillus, in which lactic acid is an end product of fermentation. Lactobacilli are important in food technology for the production of cheese, yoghurt, and other foods from milk.