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Probiotics are living microbial organisms whereas prebiotics are non-digestible food ingredients which are by selectively stimulating the growth and activity of one or a limited number of bacteria in the colon benefit our health when they are administered in the right amounts. There are many different types of probiotic cultures which can provide various benefits. Recent research shows positive affects from certain pro as well as prebiotics on intestinal microflora and/or different intestinal functions such as improving intestinal motility and managing diarrhea.
For prevention and treatment of allergic diseases also, probiotic bacteria are candidate agents. Probiotics are proposed to provide beneficial immunoregulatory signals which aid in oral tolerance achievement and alleviation of symptoms of allergic diseases. Various studies have demonstrated their positive clinical effects on the prevention and treatment of atopic diseases, but immunological effects of probiotic bacteria are poorly known..The role of probiotics and prebiotics in cancer is not hidden. Evidence also suggest from a wide range of sources supports the view that colonic microflora is involved in the aetiology of cancer. The significant contribution of prebiotics in maintaining the cvs system upright is now being scientifically proven. This review is an attempt to highlight the current aspects of prebiotics and probiotics and to be aware of the recent researches being associated with them.
Keywords: Probiotics, Prebiotics, Allergy, Colon cancer
WHAT ARE THE PROBIOTICS?
Probiotics are essentially helpful, live organisms, usually bacteria, that are used to change or re-establish the intestinal or gut flora and improve our health. They are usually given as part of our food, but can be introduced into our bodies in other ways. This whole concept of helpful bacteria may seem confusing since bacteria are usually associated with diseases and illnesses. But this is not the only role that bacteria play in our bodies. Some types of bacteria can be quite helpful and without them we would become ill.
Probiotics are the substances created when we take some of the helpful bacteria, grow them in a laboratory and when there are sufficient amounts created, we reintroduce them to the part of the body that needs them. To be termed a probiotic this organism must be alive, beneficial and safe 
WHY ARE THEY IMPORTANT?
In and on our bodies right now are billions of bacteria and other microbes. They can be found on our skin, in our mouths, in our intestines and other parts of the body. All our lives we have been living and thriving with these organisms - a relationship that is beneficial to us both. We help the microbes by giving them a place to live and food to eat. These microbes protect us simply by being there and taking up room so that there is no room for other, more harmful bacteria or by allowing our immune system to practice killing stuff . The role of helpful microbes may also be more active, in that, they produce toxins to kill harmful intruders and cancer causing compounds or they help us to digest our food and, in some cases, even provide vitamins for us.
Microbes have been shown to be important to the general health of animals. In laboratory animals grown to be microbe free, their immune systems functioned improperly and they had a reduced ability to resist disease-causing bacteria. The importance of microbes in human beings is also demonstrated when we lose our good bacteria, for example, by taking antibiotics . The antibiotics kill the good and the bad bacteria alike. Later, because the good bacteria are not there to protect us, harmful bacteria can take over various parts of our bodies like our bowels or inside the vagina and we become ill. It is thought, and in some cases shown, that probiotics can be given to help restore the balance and thus, health.
WHAT DO THEY DO?
Probiotics are believed to be helpful in the prevention and the treatment of various diseases. The most widely studied disease is diarrhoea. These studies have shown that probiotics can reduce the number of times certain types of diarrhoea occur as well as how long it lasts. One study concluded that a particular type of bacteria, lactobacillus, was a safe and effective treatment for children with acute diarrhoea. Other diseases of the bowel, such as irritable bowel syndrome which causes belly pain, cramps, gas, bloating, diarrhoea and constipation and inflammatory bowel diseases (Ulcerative colitis and Crohns disease) have also been examined . Clinical trials have shown that high levels of certain probiotics can make the disease-free period last longer or improve symptoms. Other studies are showing that probiotic cultures may be helpful in the treatment of small bowel bacteria overgrowth, helicobacter pylori growth (a bacteria that infects the stomach and is linked to the development of stomach cancer and stomach ulcers) kidney stones and elevated blood cholesterol levels. Some bacteria have been shown to reduce the blood pressure of mildly hypertensive individuals .
THERAPEUTIC MODULATION OF GUT MICROFLORA:
The gut microflora is an important constituent in the intestine's defence barrier .The initial compositional development of the gut microflora is considered a key determinant in the development of normal gut barrier functions . Specific aberrancies in the intestinal microbiota may predispose the host to disease. Intestinal mucosal defense mechanisms acting in lumen and mucosa restrict colonization by pathogenic bacteria by interfering with the adherence of microorganisms to the mucosal surface.The normal gut microbiota can prevent the overgrowth of potential pathogens in the GI tract.. Probiotics introduce new microbes to the GI tract to enhance microbiota maintenance and modification, while most prebiotic components have been shown to enhance the growth of Bifidobacterium biota. Probiotics have been shown to amplify the gut mucosal barrier functions.
CHARACTERISTICS OF GOOD PROBIOTICS:
Fuller (1989) listed the following as features of a good probiotic:
It should be a strain, which is capable of exerting a beneficial effect on the host animal, e.g. increased growth or resistance to disease.
It should be non-pathogenic and non-toxic.
It should be present as viable cells, preferably in large numbers.
It should be capable of surviving and metabolising in the gut environment e.g. resistance to low pH and organic acids
It should be stable and capable of remaining viable for periods under storage and field conditions .
A probiotic agent with all these features has considerable advantage over antibacterial supplements such as antibiotics currently in use. They do not induce resistance to antibiotics, which will compromise therapy. They are not toxic and therefore will not produce undesirable side effects when being fed and in the case of food animals, will not produce toxic residues in the carcass.They may stimulate immunity whereas the immune status remains unaffected by antibiotics. An essential determinant in the choice of a probiotic microorganism is its ability to reach, survive, and persist in the environment in which it is intended to act .
PROBIOTICS - MECHANISM OF ACTION:
Mechanisms for the benefits of probiotics are incompletely understood. However, as a general rule, include
â€¢ Adherence and colonization of the gut.
â€¢ Suppression of growth or epithelial binding/invasion by pathogenic bacteria and production of antimicrobial substances.
â€¢ Improvement of intestinal barrier function.
â€¢ Controlled transfer of dietary antigens.
â€¢ Stimulation of mucosal and systemic host immunity.
The term prebiotic was introduced by Gibson and Roberfroid who exchanged "pro" for "pre," which means "before" or "for." They defined prebiotics as "a non-digestible food ingredient that beneficially affects the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon." This definition more or less overlaps with the definition of dietary fiber, with the exception of its selectivity for certain species. This selectivity was shown for bifidobacteria, which may be promoted by the ingestion of substances such as fructooligosaccharides and inulin transgalactosylated oligosaccharides (and soybean oligosaccharides) 
Prebiotics act as an alternative for probiotics or their cofactors. Complex carbohydrates pass through the small intestine to the lower gut where they become available for some colonic bacteria but are not utilized by the majority of the bacteria present in the colon. Lactulose, galactooligosaccharides, fructooligosaccharides, inulin and its hydrolysates, maltooligosaccharides, and resistant starch are prebiotics commonly used in human nutrition. The main end products of carbohydrate metabolism are short-chained fatty acids, namely acetate, butyrate and propionate, which are further used by the host organism as an energy source. . Prebiotic oligosaccharides can be produced in three different ways: by extraction from plant materials, microbiological synthesis or enzymatic synthesis, and enzymatic hydrolysis of polysaccharides . The majority of prebiotic oligosaccharides is produced on the industrial scale and is widely available on the market.
PROBIOTICS AND THEIR POTENTIAL IN ALLERGY:
Epidemiological and experimental studies suggest that changes in gut microbial balance are associated with increases in the prevalence of allergic diseases. For prevention and treatment of allergic diseases, probiotic bacteria are candidate agents. Probiotics are proposed to provide beneficial immunoregulatory signals which aid in oral tolerance achievement and alleviation of symptoms of allergic diseases. Previous studies have demonstrated their positive clinical effects on the prevention and treatment of atopic diseases, but immunological effects of probiotic bacteria are poorly known.
Studies conducted by "Emma Marschan, on Immunological effects of probiotics bacteria in prevention and treatment of allergic diseases in childrens" Probiotic bacteria are an attractive possibility for an immunomodulatory approach in early allergic diseases, but the immunological effects of probiotic bacteria are poorly known. Our results show an association between CBMC immune responses and IgE-sensitization at age 2, and highlight the immunological effects of probiotic bacteria in infants with allergic diseases and in infants at genetic risk for allergies . The main conclusions of the study are:
1. Priming of GATA-3 and the IL-5 pathway may occur in utero. Higher GATA-3 expression and IL-2 and IL-5 secretion of stimulated CBMCs were detected in IgE-sensitized infants at age 2 than in non-allergic, non-sensitized infants. A primary feature in T-cells predisposing to IgE-sensitization seems to directly favour Th2 deviation.
2. Immunological effects of probiotic bacteria are modulated by the host. Differing immunological responses were apparent in the infants with differing clinical outcomes. The probiotic mixture raised plasma IL-10 levels, while IL-6 levels increased after Lactobacillus GG treatment, suggesting that the immune response induced by probiotics is strain-specific.
3. Low-grade inflammation may control tolerance achievement and generate protection from eczema. In infants with IgE-associated eczema, Lactobacillus GG treatment induced an increase in plasma CRP and IL-6 levels. When the probiotic mixture given to infants at high risk for allergic diseases, raised plasma CRP level. A higher CRP level at age 6 months was associated with decreased risk for eczema at age 2. A CRPassociated decrease in risk for eczema was not restricted to probiotic use.
4. The beneficial immunomodulatory effects of probiotic bacteria in infants resemble immune profiles that are characteristic for chronic low-grade inflammation, a response resembling that of helminth-like infections. The probiotic induced response in infants at high risk for allergic diseases was characterised by an increase in plasma IL-10, total IgE, and CRP levels, without induction of an allergen-specific IgE response. Bacteria stimulate innate immunity, as seen in increased plasma CRP levels. Increased plasma CRP level at age 6 months was associated with reduced risk for eczema at age 2. Probiotic bacteria stimulate Th1 and Th2 immunity via their effect on APCs. Different probiotic strains had differing immunostimulatory effects, and effects of probiotic bacteria seem to be modulated by the host.
The probiotic mixture raised plasma total IgE, IL-10, and CRP levels, without induction of an allergen-specific IgE. The beneficial immunomodulatory effects of probiotic bacteria in infants resemble immune profiles that are characteristic for chronic low-grade inflammation.
PROBIOTICS, PREBIOTICS AND THEIR ROLE IN COLON CANCER:
Yoghurt, and the lactic acid producing bacteria (LAB; probiotics) that it contains, have received much attention as potential cancer-preventing agents in the diet. It is usually considered that the mechanism of the action is by increasing the numbers of LAB in the colon, which modifies the ability of the microflora to produce carcinogens. Prebiotics such as nondigestible oligosaccharides (NDO) appear to have similar effects on the microflora by selectively stimulating the growth of LAB in the colon . Some of these studies indicate that combinations of pro and prebiotics ('synbiotics') are more effective. Evidence that probiotics and prebiotics can influence carcinogenesis is derived from a variety of sources:
â€¢ Effects on bacterial enzyme activities.
â€¢ Antigenotoxic effects in vitro and in vivo.
â€¢ Effects on pre-cancerous lesions in laboratory animals.
â€¢ Effects on tumour incidence in laboratory animals
â€¢ Epidemiological and experimental studies in humansEffects of Probiotics and
Prebiotics on Bacterial
EFFECT OF PROBIOTICS AND PREBIOTICS ON BACTERIAL ENZYME ACTIVITIES:
The ability of the colonic microflora to generate a wide variety of mutagens, carcinogens and tumour promoters from dietary and endogenously-produced precursors is well documented. For example, the enzyme ß-glucuronidase is involved in the release in the colon, from their conjugated form, of a number of dietary carcinogens, including polycyclic aromatic hydrocarbons. Similarly, bacterial ß-glycosidase hydrolyzes the plant glycoside cycasin to a carcinogen in the gut. It should be noted however that glycoside hydrolysis by intestinal microflora can result in the generation of potential anti-carcinogenic and anti-mutagenic substances in the form of flavonoids such as quercetin. A major role for the intestinal microflora has been identified in the metabolism of the bile acids cholic and chenodeoxycholic acids to deoxycholic and lithocholic acids, which are thought to possess tumour-promoting activity. Other potential tumour promoters, namely ammonia, phenols and cresols, are also generated by deamination of amino acids such as tyrosine by intestinal bacteria.
The reaction of nitrite with secondary amines and amides can lead to the formation of N-nitroso compounds, many of which possess mutagenic and carcinogenic activity. There is evidence from germ-free rat studies that nitrosation can occur under neutral pH conditions by an enzymic process catalysed by intestinal bacteria. Another bacterially-catalysed reaction yielding a reactive substance capable of causing DNA damage and mutation, is the conversion of the cooked food carcinogen 2-amino-3-methyl-3H-imidazo (4,5-f) quinoline (IQ) to its 7- hydroxy derivative. The latter, unlike its parent compound is a direct-acting mutagen In general, species of Bifidobacterium and Lactobacillus, have low activities of these enzymes involved in carcinogen formation and metabolism by comparison to other major anaerobes in the gut such as bacteroides, eubacteria and clostridia .This suggests that increasing the proportion of LAB in the gut could modify, beneficially, the levels of xenobiotic metabolising enzymes.
Studies have been carried out in laboratory animals and humans in order to acquire a greater understanding of the way in which administration of specific probiotics and prebiotics affect gut microflora metabolism.
EFFECTS OF PROBIOTICS ON THE IMMUNE SYSTEM:
It has been investigated extensively about all the different potentials of probiotics to stimulate the immune system of the host. It has been discovered that conventional animals with a complete gut flora have increased phagocytic activity and immunoglobulin levels compared with germ-free animals. Yoghurt has been shown to increase antibody levels when fed to germ free mice. Lactobacilli casei in particular was found to be active in the stimulation of phagocytic activity when administered to mice. For bacteria it is effective in the process of immunostimulation, it may be necessary for them to migrate from the gut to the systemic circulation. Lactobacilli had been found to be capable of translocating and surviving for many days in the spleen, liver, and lungs. Immune modulation of blood leukocytes in humans by lactic acid bacteria (LAB) had also been observed. Many investigations have reported that oral ingestion of LAB by rats increases lymphocyte proliferation and interferon production. They suggested that beneficial consequences might be obtained by an increase in resistance to some infections. Studies in rats and mice reveal that lactic acid bacteria administered orally increase the numbers of T lymphocytes, CD4+ cells and antibody-secreting cells, including those in the intestinal mucosa, and enhance lymphocyte proliferation, natural killer cell activity, IL-1, TNF and IFN-_ production, antibody production (including secretory IgA), phagocytic activity and the respiratory burst of macrophages and the DTH response .
ANTIHYPERTENSIVE MECHANISMS OF PREBIOTICS:
Various mechanisms have been postulated to explain the ability of prebiotics to reduce the risk of hypertension. One of the possible mechanisms is via the lowering of blood lipid and cholesterol. Previous studies have demonstrated that intensive reduction of cholesterol may be beneficial in the treatment of patients with isolated systolic hypertension . The lipid and cholesterol lowering effects of prebiotics could be attributed to the production of short chain fatty acids (SCFA). It is commonly known that prebiotics resist digestion in the small intestine and reach the colon, where they are fermented by selective colonic microflora to produce SCFA such as acetate, propionate and lactate. The SCFA produced in the large bowel are absorbed in the portal vein, and a major part is metabolized by the liver and subsequently affects various metabolic processes. Indigenous lactic acid bacteria and bifidobacteria often have the ability to ferment these indigestible prebiotics and produce lactate and acetates as the main metabolites, with smaller amounts of propionate and butyrate . It has been reported that propionate could hinder fatty acid and cholesterol synthesis, while lactate produced in the colon plays a significant role in lowering the synthesis of triaclyglycerol fatty acids. Soluble prebiotics such as pectin, konjac mannan and modified starches are soluble in solutions leading to a thickening and viscous effect. Such physicochemical properties have been found to affect physiological responses such as the lowering of blood cholesterol, and increasing satiety by delaying speed of gastric transit in the upper gastrointestinal tract ,.
CURRENT RESEARCHES BEING CARRIED OUT IN THE FIELD OF PREBIOTICS AND PROBIOTICS:
Currently, a widely marketed prebiotic, inulin is extracted from plants of the family Asteraceae .There are many unexploited plants that are regularly consumed and that may have a prebiotic effect or can have very high levels of inulin which could make them commercially viable. Some of the plants kept under investigation are:
In an investigation being carried out on the aqueous extracts of 22 plants from the families Asparagaceae, Alliaceae, Asteraceae, Solanaceae, Cucurbitaceae, Amaranthaceae, Acanthaceae, Polygonaceae, Portulaceae, Fabaceae, Chenopodiaceae, Pedaliaceae and Apiaceae for a prebiotic effect using a modified batch-culture technique with Lactobacillus bulgaricus, Lactobacillus lactis, Lactobacillus reuteri and Bifidobacterium longum, four common probiotics and the inulin content of the plants was determined using high performance liquid chromatography . Out of the 22 plants studied, Solanum nigrum, Amaranthus spinosus, Amaranthus hybridus, Asystasia gangetica, Senna occidentalis, Cerathoteca triloba, Asparagus sprengeri, Tulbaghia violacea, Sonchus oleraceus and Taraxacum officinale exhibited a prebiotic effect. The prebiotic effect of the Taraxacum officinale, Sonchus oleraceus and Asparagus sprengeri extracts on L. lactis and L. reuteri was higher than or equivalent to inulin-a commercial prebiotic. In this study, Sonchus oleraceus exhibited the best prebiotic effect-was the only plant to stimulate all the probiotics including B. longum. All the plants analysed, Asparagus sprengeri tuber contained the highest amount of inulin.
USES OF PRE AND PRO-BIOTICS:
This bacterial "balancing act" can be thrown off in two major ways:
1. By antibiotics, when they kill friendly bacteria in the gut along with unfriendly bacteria. Some people use probiotics to try to offset side effects from antibiotics like gas, cramping, or diarrhea. Similarly, some use them to ease symptoms of lactose intolerance-a condition in which the gut lacks the enzyme needed to digest significant amounts of the major sugar in milk, and which also causes gastrointestinal symptoms.
2. "Unfriendly" microorganisms such as disease-causing bacteria, yeasts, fungi, and parasites can also upset the balance. Researchers are exploring whether probiotics could halt these unfriendly agents in the first place and/or suppress their growth and activity in conditions like:
Irritable bowel syndrome
Inflammatory bowel disease (e.g., ulcerative colitis and Crohn's disease) Infection with Helicobacter pylori (H. pylori), a bacterium that causes most ulcers and many types of chronic stomach inflammation
Tooth decay and periodontal disease
Stomach and respiratory infections that children acquire in daycare
Prebiotics are capable of reducing and preventing hypertension.
SIDE EFFECTS AND RISKS:
Some live microorganisms have a long history of use as probiotics without causing illness in people. Probiotics' safety has not been thoroughly studied scientifically, however. More information is especially needed on how safe they are for young children, elderly people, and people with compromised immunity.
Probiotics' side effects, if they occur, tend to be mild and digestive (such as gas or bloating). More serious effects have been seen in some people . Probiotics might theoretically cause infections that need to be treated with antibiotics, especially in people with underlying health conditions. They could also cause unhealthy metabolic activities, too much stimulation of the immune system, or gene transfer (insertion of genetic material into a cell).
It is being noticed that alteration in the gut microflora can lead to a number of modifications not only in our health aspects but also in present mode of drug administration. The utility of probiotics and prebiotics either separately or in the form of synobiotics can change our concept towards vital diseases like cancer, cardiovascular diseases, allergies etc.With the advancement of time and scientific approaches the other fundamentals of prebiotics and probiotics will be enlighten.
Probiotics are live microbial food supplements or components of bacteria, which have been shown to have beneficial effects on human health. Normalization of the properties of unbalanced indigenous microflora of the intestinal tract by ingestion of specific strains of the healthy microflora forms the rationale of probiotic therapy. Prebiotic, probiotic and synbiotic treatment is still in its infancy but is rapidly moving into the mainstream.
Genetically modified lactic acid bacteria have been proposed as a vehicle to deliver vaccines in the gastro-intestinal tract. Several secretion-expression probiotic vectors have been constructed and are currently being tested in animal models. Other probiotics carrying different immunomodulating molecules are currently being tested. Also, the probiotic vector have been modified to provide a way to deliver the active ingredient at specific targets in the gastrointestinal tract .Various processing advances, such as microencapsulation and bacterial coating and addition of prebiotic compounds used as growth factors for probiotic organisms, will provide a means to optimize the delivery and survival of strains at the site of action. Genetic approaches also will enable design of genetically modified probiotic strains with specific theraÂpeutic capabilities such as delivery of anti-inflammatory cytokines, vaccine epitopes, or antipathogenic molecules. Well-designed and properly controlled human and mechanistic studies will advance the essential understanding of active principles, mechanisms of action, and degree of effects that can be realÂized by specific consumer groups.