Lactobacillus

Lactobacillus is a genus of Gram-positive facultative anaerobic or microaerophilic bacteria.Abedon, Stephen T. (May 6, 1998). "Supplemental Lecture" They are a major part of the lactic acid bacteria group, named as such because most of its members convert lactose and other sugars to lactic acid. They are common and usually benign. In humans they are present in the vaginaDicks, LMT; M. Silvester, PA Lawson, MD Collins (2000). "Lactobacillus fornicalis sp. nov., isolated from the posterior fornix of the human vagina". International Journal of Systematic and Evolutionary Microbiology (Society for General Microbiology) 50: 1253–8. ISSN 1466-5034 and the gastrointestinal tract, where they are symbiotic and make up a small portion of the gut flora. Many species are prominent in decaying plant material. The production of lactic acid makes its environment acidic, which inhibits the growth of some harmful bacteria. Several members of the genus have had their genome sequenced.Ljungh, Åsa; Wadström, Torkel, eds. (2009), 'Lactobacillus Molecular Biology: From Genomics to Probiotics, Caister Academic Press, ISBN 978-1-904455-41-7

Some Lactobacillus species are used industrially for the production of yogurt, cheese, sauerkraut, pickles, beer, wine, cider, kimchi, chocolate, and other fermented foods, as well as animal feeds, such as silage. Sourdough bread is made using a "starter culture," which is a symbiotic culture of yeast and lactic acid bacteria growing in a water and flour medium. Lactobacilli, especially L. casei and L. brevis, are some of the most common beer spoilage organisms. The species operate by lowering the pH of the fermenting substance by creating the lactic acid, neutralising it to the desired extent.

Some Lactobacillus spp. and other lactic acid bacteria may possess potential therapeutic properties including anti-inflammatory and anti-cancer activities, as well as other features of interest. A study by Xinhua Chen, Johannes Fruehauf, Jeffrey D. Goldsmith, Hua Xu, Kianoosh K. Katchar, Hon-wai Koon, Dezheng Zhao, Efi G. Kokkotou, Charalabos Pothoulakis, and Ciaran P. Kelly (2009) demonstrated the protective effects of some strains of these bacteria for anti-tumor and anti-cancer effects. Dietary administration alleviated the risks of certain types of cancers and suppressed colonic tumor incidence, volume and multiplicity induced by various carcinogens. For a few strains oral administration effectively reduced DNA adduct formation, ameliorated DNA damage and prevented putative preneoplastic lesions such as aberrant crypt foci induced by chemical carcinogens in the gastrointestinal tract. Reports also indicated that some cultures administered to animals inhibited liver, colon, bladder, and mammary tumors, highlighting potential systemic effects of probiotics with anti-neoplastic activities.

Lactobacilli are also used to restore particular physiological balance such as in the vaginal eco-system (Gynoflor). Their role is (1) to physically protect the vaginal epithelium by building a thick layer separating the epithelium from pathogens, (2) to physiologically keep the balance of the vaginal ecosystem in maintaining the pH at ~4.5 and (3) generating hydrogen peroxide against pathogens.

The genus Lactobacillus currently consists of over 125 species and encompasses a wide variety of organisms. The genus is polyphyletic, with the genus Pediococcus dividing the L. casei group, and the species L. acidophilus, L. salivarius, and L. reuteri being representatives of three distinct subclades. The genus Paralactobacillus falls within the L. salivarius group. In recent years, other members of the genus Lactobacillus (formerly known as the Leuconostoc branch of Lactobacillus) have been reclassified into the genera Atopobium, Carnobacterium, Weissella, Oenococcus, and Leuconostoc. More recently, the Pediococcus species P. dextrinicus has been reclassified as a Lactobacillus species (IJSEM, Paper in Press).

Although considered beneficial, some Lactobacillus species have been associated with dental caries. Lactobacillus count in saliva has been used as a "caries test" for many years. This is one of the arguments used in support of the use of fluoride in toothpaste and lozenges.Tasli, L.; C. Mat, C. De Simone, H. Yazici (September-October 2006). "Lactobacilli lozenges in the management of oral ulcers of Behçet's syndrome.". Clinical and Experimental Rheumatology 24 (5 Suppl 42): S83-6. ISSN 1593-098X

Many lactobacilli are unusual in that they operate using homofermentative metabolism (that is, they produce only lactic acid from sugars in contrast to heterofermentative lactobacilli which can produce either alcohol or lactic acid from sugars) and are aerotolerant despite the complete absence of a respiratory chain. This aerotolerance is manganese-dependent and has been explored (and explained) in Lactobacillus plantarum. Many lactobacilli do not require iron for growth and have an extremely high hydrogen peroxide tolerance.

According to metabolism, Lactobacillus species can be divided into three groups:

• Obligately homofermentative (Group I)
  • L. acidophilus, L. delbrueckii, L. helveticus, L. salivarius
• Facultatively heterofermentative (Group II)
  • L. casei, L. curvatus, L. plantarum, L. sakei
• Obligately heterofermentative (Group III)
  • L. brevis, L. buchneri, L. fermentum, L. reuteri