Numbered ticks are 11 µm
Hansen & Mocquot 1970
Lactobacillus acidophilus (Latin meaning acid-loving milk-bacterium) is a species in the genus Lactobacillus. L. acidophilus is a homofermentative species, fermenting sugars into lactic acid, and grows readily at rather low pH values (below pH 5.0) and has an optimum growth temperature of around 37 °C (99 °F). L. acidophilus occurs naturally in the human and animal gastrointestinal tract, mouth, and vagina. Some strains of L. acidophilus may be considered to have probiotic characteristics. These strains are commercially used in many dairy products, sometimes together with Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus in the production of acidophilus-type yogurt.
Health effects 
Some strains of L. acidophilus have been studied extensively for health effects. Some L. acidophilus strains may be able to survive gastrointenstinal transit, being resistant to bile, low pH, and digestive enzymes. They may then be able to adhere to human epithelial cell lines and human intestinal mucus.
A blend of bacterial strains including L. acidophilus NCFM decreased the incidence of pediatric diarrhea. L. acidophilus led to a significant decrease in levels of toxic amines in the blood of dialysis patients with small bowel bacterial overgrowth. At adequate daily feeding levels, L. acidophilus may facilitate lactose digestion in lactose-intolerant subjects.
A University of Nebraska study found that feed supplemented with L. acidophilus L1 and fed to cattle resulted in a 61% reduction of Escherichia coli O157:H7. Research has indicated L. acidophilus may be helpful reducing serum cholesterol levels.
Antibiotics taken orally will also kill beneficial bacteria, including L. acidophilus. After a therapy that includes antibiotics, patients are occasionally instructed to take an L. acidophilus treatment in order to recolonize the gastrointestinal tract. To that effect, L. acidophilus is often sold in health stores in pill or powder form as a nutritional supplement, as well as being available in many yogurts. A part of the claims in favor of such treatment refer to attaining a better digestion thanks to a recovered normal intestinal flora. L. acidophilus LA-5 produces bacteriocin CH5 that is both antibacterial and inhibitory against certain yeasts and molds and is effective against both Salmonella typhimurium and Campylobacter jejuni. It has been shown to improve bowel regularity and has been shown to have a preventative effect against traveller's diarrhea, as well as antibiotic related bowel issues.
Because of its relation to gut-associated lymphoid tissue (GALT), L. acidophilus LA-5 has been associated with positive effects on the immune system such as increased cytokine, phagocytic activity and antibody production, as well as phagocytosis of Salmonella, and L. acidophilus NCFM has even been shown to reduce incidence of symptoms of fever, cough and runny nose. Anti-inflammatory effects have also been observed in people consuming L. acidophilus NCFM. Additionally L. acidophilus LA-5 has shown to inhibit growth of breast cancer cells, and positive effects on chemotherapy patients. An improvement of lipid metabolism has also been linked to L. acidophilus LA-5.
Animal studies of NCFM have indicated that it reduces intestinal pain by inducing u-opioid and canabinoid receptors in the intestines (of animals), but this effect has not been sufficiently shown in humans yet.
Other benefits of L. acidophilus include the production of vitamin K and lactase, and some strains may produce bacteriocins such as acidolin, acidophilin and lactocidin.
A study published in the Journal of the American College of Nutrition reported that yogurt containing L. acidophilus L1 has the potential to reduce risk for coronary heart disease by 6–10% by reducing serum cholesterol concentration.
Although a study that evaluated the effects of L. acidophilus on the symptoms of Japanese cedar-pollen allergy achieved positive results, this still needs further research.
Uses for lactose intolerance 
There are many fermented dairy products that use L. acidophilus including yogurt and some types of cheese. Sweet acidophilus milk is consumed by individuals who suffer from lactose maldigestion and intolerance, which occurs when enzymes (lactase) cannot break down lactose (milk sugar) in the intestine. Failure to digest lactose results in discomfort, cramps and diarrhea. Some bacteria have been shown to improve lactose digestion by providing β-galactosidase, while some L. acidophilus strains have been linked to improvement in symptoms and indicators of lactose indigestion.
Strains with described health effects 
|Strain||Brandname||Producer||Proven effect in humans|
|Lactobacillus acidophilus DDS-1||Nebraska Cultures|
|Lactobacillus acidophilus LA-5||Chr. Hansen|
|Lactobacillus acidophilus NCFM||Danisco|
Vaginal microbiota(flora) 
While Lactobacillus species are part of the vaginal flora, the most common species are Lactobacillus crispatus, L. gasseri, L. jensenii, and L. iners -- modern identification methods have not found L. acidophilus to be common in the vagina. In lab experiments, L. acidophilus seemed to decrease Candida albicans’ ability to adhere to vaginal epithelial cells; however, L. acidophilus’ role in preventing yeast infections is unclear because this species of Lactobacilli has also been found not to have a very strong ability to adhere to (and thereby colonize) the vaginal cells.
Certain spermicides and contraceptive creams can kill Lactobacillus species in the vagina, clearing the path to possible yeast infections.
Side effects 
In general, the ingestion of L. acidophilus is safe. However, people with some conditions should be encouraged to consult their healthcare provider prior to taking L. acidophilus supplements including those who are immunosuppressed or are on immunosuppressant drugs and those who have short bowel syndrome.
Scant complaints of mild gastrointestinal discomfort or gas have been noted.
See also 
- Bâati, L. ̈L.; Fabre-Gea, C.; Auriol, D.; Blanc, P. J. (2000). "Study of the cryotolerance of Lactobacillus acidophilus: Effect of culture and freezing conditions on the viability and cellular protein levels". International Journal of Food Microbiology 59 (3): 241–247. doi:10.1016/S0168-1605(00)00361-5. PMID 11020044.
- "Bacteria Genomes – LACTOBACILLUS ACIDOPHILUS". European Bioinformatics Institute. Retrieved 2007-08-22.
- Ljungh A, Wadström T (2006). "Lactic acid bacteria as probiotics". Curr Issues Intest Microbiol 7 (2): 73–89. PMID 16875422.
- Yuan-Kun Lee  (2009). Rev. ed. of: Handbook of probiotics 2nd ed. Hoboken, N.J. : John Wiley & Sons. pp. 441–443. ISBN 978-0-470-13544-0 0470135441 Check
- "Lactobacillus acidophilus". Natural Medicines Comprehensive Database, Consumer Version. Medline Plus. Retrieved April 20, 2012.
- Sanders ME, Klaenhammer TR (2001). "Invited review: the scientific basis of Lactobacillus acidophilus NCFM functionality as a probiotic". J Dairy Sci 84 (2): 319–331. doi:10.3168/jds.S0022-0302(01)74481-5. PMID 11233016.
- http://ard.unl.edu/rn/0902/ecoli.html[dead link]
- Anderson J, Gilliland S (1999). "Effect of fermented milk (yogurt) containing Lactobacillus acidophilus L1 on serum cholesterol in hypercholesterolemic humans". J Am Coll Nutr 18 (1): 43–50. PMID 10067658.
- "Effect of Fermented Milk (Yogurt) Containing Lactobacillus acidophilus L1 on Serum Cholesterol in Hypercholesterolemic Humans". Retrieved May 25, 2010.
- "Lactobacillus acidophilus". Retrieved May 25, 2010.
- de Roos N, Katan M (1 February 2000). "Effects of probiotic bacteria on diarrhea, lipid metabolism, and carcinogenesis: a review of papers published between 1988 and 1998". Am J Clin Nutr 71 (2): 405–11. PMID 10648252.
- "About us". Nebraska Cultures. Retrieved 2009-11-07.
- Forsum U, Holst E, Larsson P, Vasquez A, Jakobsson T, Mattsby-Baltzer I (2005). "Bacterial vaginosis—a microbiological and immunological enigma". APMIS 113 (2): 81–90. doi:10.1111/j.1600-0463.2005.apm1130201.x. PMID 15723682.
- Holmes, King, et al. Sexually Transmitted Diseases. McGraw-Hill Professional; 4 edition (December 14, 2007). pg. 294: "The lack of reliable plenotypic methods for identification of lactobacilli have led to a broad misunderstanding of the species of lactobacilli present in the vagina, and the common misperception that dairy and food derived lactobacilli are similar to those found in the vagina."
- Can Yogurt Prevent Yeast Infections?. Planned Parenthood Advocates of Arizona. 28 February 2012. Retrieved 28 February 2012.
- Lactobacillus at MedlinePlus
- Lactobacillus acidophilus at University of Maryland Medical Center
- Lactobacillus acidophilus from the U. of Wisconsin
- Global analysis of carbohydrate utilization by Lactobacillus acidophilus using cDNA microarrays
- Safety and protective effect of Lactobacillus acidophilus and Lactobacillus casei used as probiotic agent in vivo