Probiotic has been defined as "live microorganisms which when administered in adequate amounts confer a health benefit on the host" as determined by an expert panel convened by the FAO (1).

Actions of probiotics
Probiotic bacteria benefit the host by adhering to the gut epithelium, stimulating host immune response, inhibiting epithelial and mucosal adherence of pathogens and producing antimicrobial substances (2). Probiotics have the potential to impact physiologic and metabolic parameters which are influenced by normal indigenous microbes, such as immune system maturation, gut barrier function, levels of metabolic end products available to alter luminal conditions or serve as substrates to epithelial cells, binding or degradation of potential carcinogens, enzymatic alteration of bile acids and competitive exclusion. (3)

Uses of probiotics
There has been increasing evidence in the last decade for efficacy of probiotic agents in treatment of acute diarrhea (2), persistent diarrhea (4), and prevention of antibiotic associated diarrhea (5). Other benefits that have been documented are regulation of immune function, (6) prevention of infection, (7) prolongation of remission in patients with inflammatory bowel conditions, (8) reduction of incidence of atopic dermatitis in high risk infants, (9) control of symptoms associated with lactose intolerance, (10) decreasing symptoms for irritable bowel syndrome, (11) prevention of Helicobacter pylori colonization, (12) vaginal microbiota restoration, (13) improve growth parameters in undernourished children, (14) decrease incidence of dental caries, (15) and respiratory infections. (16)

It should be remembered that these effects have been observed for only one or a limited number of strains and other strains of even the same species cannot be presumed to demonstrate the same effects. (3)

Common probiotics used
Members of the genera Lactobacillus and Bifidobacterium are mainly used as probiotics in food supplements, but not exclusively, as probiotic microorganisms and a growing number of probiotic foods are available to the consumer. (1)

Bifidobacterium species have a long history of safe use when consumed as part of food and supplement products. (17) No cases of clinical infection have been reported from such use. The species generally used for such applications are longum, infantis, breve, bifidum, adolescentis, and animalis (both subspecies lactis and animalis). (3)

Lactobacillus converts lactose and other sugars to lactic acid. The genus Lactobacillus currently consists of over 125 species and encompasses a wide variety of organisms. According to metabolism, the commonly used lactobacilli as probiotics are lactobacillus acidophilus, lactobacilli casei.

Probiotics should not be given to children who are seriously or chronically ill until the safety of administration has been established. With the exception of one strain belonging to the L. rhamnosus species, lactobacilli and bifidobacteria used for food production are "generally recognized as safe" (GRAS) by the Food and Drug Administration of the USA. The two strains of lactobacilli and bifidobacteria are classified as absolutely safe. (18)
Effect of probiotics on health: Several mechanisms have been postulated regarding action of probiotics. Probiotic bacteria especially lactobacillus has proven beneficial effects on intestinal immunity. It increases the number of IgA and other immunoglobulin secreting cells in the intestinal mucosa, stimulates local release of interferons and facilitates antigen transport to underlying lymphoid cells, which serves to increase antigen uptake in Peyer's patches.(6) Partial lactose digestion and stimulation of the intestinal mucosal lactase activity has been postulated as a possible mechanism against some types of diarrhea.(5) Probiotics prevent colonization of pathogens by competitive inhibition.(7) The other suggested mechanisms are lowering intestinal pH, release of gut protective metabolites, regulation of intestinal motility and mucus production.(5) At adequate daily feeding levels, lactobacillus acidophilus NCFM, a probiotic strain available in conventional foods (milk, yogurt and dietary supplements) may facilitate lactose digestion in lactose intolerant subjects.(8)

Clinical uses of probiotics: Randomized double-blind studies have provided evidence of probiotic effectiveness for the treatment and prevention of acute diarrhea and antibiotic-induced diarrhea, as well as for the prevention of cow milk-induced food allergy in infants and young children(9-11). There are also studies indicating that probiotics may be useful for prevention of respiratory infections in children, dental caries, irritable bowel syndrome and inflammatory bowel disease and urinary tract infections(12-16). Studies have reported modification of allergic reactions for atopic eczema when supplemented with probiotics especially Lactobacillus GG(17).

Necrotizing enterocolitis (NEC) occurs more in low birth weight preterm children. It is found that stools of these infants contains less lactobacillus and bifidobacterium than the controls(5) and trial with probiotic supplementation resulted in 60% reduction in NEC and overall mortality in 1237 newborns in Columbia(18).

Probiotics have an in vitro inhibitory effect, reduced H.pylori associated gastric inflammation in animals, improved H.pylori associated gastritis and also probiotic treatment reduced H. pylori therapy associated side effects.(19)

Use of probiotics in healthy children: Consumption of probiotics presents a negligible risk to consumers(20) though there have been cases of sepsis secondary to Lactobacillus rhamnosus GG reported(21) especially when the organism is enterococcus and patient is immunocompromised. However study in healthy preschoolers and children taking 6 months of probiotic have found to reduce fever incidence by 53% - 72.7%, coughing incidence by 41.4% - 62.1% and rhinorrhea by 58.8% and lead to reduction in days absent from group child care by 27.7% - 31.8% suggesting that long term probiotic supplementation was safe and effective way to reduce fever, rhinorrhea, cough and number of missed school days in these children(22).

Conclusion: Data suggests that probiotics may promote good health in day care and work settings and may decrease incidence of infections in healthy as well as ill children. Long term consumption of probiotics appears to be safe.
1. Health and Nutritional Properties of Probiotics in Food including Powder Milk with Live Lactic Acid Bacteria, Report of a Joint FAO/WHO Expert Consultation, Cordoba, Argentina, 1?4 October 2001, Available at: Accessed February 10, 2006.
2. Szajewska H, Mrukowicz JZ. Use of probiotics in children with acute diarrhea. Paediatr Drugs. 2005;7:111-122
3. Sanders ME. Summary of probiotic activities of Bifidobacterium lactis HN019. J Clin Gastroenterol. 2006; 40: 776-783
4. Basu S, Chatterjee M, Ganguly S, Chandra PK. Effect of Lactobacillus rhamnosus GG in persistent diarrhea in Indian children: a randomized controlled trial. J Clin Gastroenterol. 2007;41:756-760
5. Szajewska H, Ruszczynski M, Radzikowski A. Probiotics in the prevention of antibiotic-associated diarrhea in children: a meta-analysis of randomized controlled trials. J Pediatr. 2006;149:367?372
6. Gill HS. Probiotics to enhance anti-infective defences in the gastrointestinal tract. Best Pract Res Clin Gastroenterol. 2003;17:755-773.
7. Bengmark S. Use of some pre-, pro- and synbiotics in critically ill patients. Best Pract Res Clin Gastroenterol. 2003;17:833-848.
8. Tamboli CP, Caucheteux C, Cortot A, et al. Probiotics in inflammatory bowel disease: a critical review. Best Pract Res Clin Gastroenterol. 2003;17:805-820.
9. Kalliomaki M, Salminen S, Poussa T, et al. Probiotics and prevention of atopic disease: 4-year follow-up of a randomised placebo-controlled trial. Lancet. 2003;361:1869-1871.
10. de Vrese M, Stegelmann A, Richter B, et al. Probiotics?compensation for lactase insufficiency. Am J Clin Nutr. 2001;73(suppl 2):421S-429S.
11. Saggioro A. Probiotics in the treatment of irritable bowel syndrome. J Clin Gastroenterol. 2004;38(suppl 6):S104-S106.
12. Wang KY, Li SN, Liu CS, et al. Effects of ingesting Lactobacillus- and Bifidobacterium-containing yogurt in subjects with colonized Helicobacter pylori. Am J Clin Nutr. 2004;80:737-741.
13. Reid G, Charbonneau D, Erb J, et al. Oral use of Lactobacillus rhamnosus GR-1 and L. fermentum RC-14 significantly alters vaginal flora: randomized, placebo-controlled trial in 64 healthy women. FEMS Immunol Med Microbiol. 2003;35:131-134.
14. Saran S, Gopalan S, Krishna TP. Use of fermented foods to combat stunting and failure to thrive. Nutrition. 2002;18:393?396.
15. Nase L, Hatakka K, Savilahti E, et al. Effect of long-term consumption of a probiotic bacterium, Lactobacillus rhamnosus GG, in milk on dental caries and caries risk in children. Caries Res. 2001;35:412-420.
16. Hatakka K, Savilahti E, Ponka A, et al. Effect of long term consumption of probiotic milk on infections in children attending day care centres: double blind, randomised trial. BMJ. 2001;322:1327.
17. Borriello SP, Hammes WP, Holzapfel W, et al. Safety of probiotics that contain lactobacilli or bifidobacteria. Clin Infect Dis. 2003;36:775?780.
18. Boriello SP, Hammes WP, Holzapfel W, Marteau P, Schrezenmeir J, Vaara M, Valtonen V. (2003) Safety of probiotics that contain lactobacilli or bifidobacteria. Clin Infect Dis 36:775-780
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