Probiotic

Probiotics are live microorganisms thought to be beneficial to the host organism. According to the currently adopted definition by FAO/WHO, probiotics are: "Live microorganisms which when administered in adequate amounts confer a health benefit on the host". Lactic acid bacteria (LAB) and bifidobacteria are the most common types of microbes used as probiotics; but certain yeasts and bacilli may also be helpful. Probiotics are commonly consumed as part of fermented foods with specially added active live cultures; such as in yogurt, soy yogurt, or as dietary supplements.

Etymologically, the term appears to be a composite of the Latin preposition pro ("for") and the Greek adjective βιωτικός (biotic), the latter deriving from the noun βίος (bios, "life").

At the start of the 20th century, probiotics were thought to beneficially affect the host by improving its intestinal microbial balance, thus inhibiting pathogens and toxin producing bacteria. Today, specific health effects are being investigated and documented including alleviation of chronic intestinal inflammatory diseases, prevention and treatment of pathogen-induced diarrhea, urogenital infections, and atopic diseases.

To date, the European Food Safety Authority has rejected most claims that are made about probiotic products, saying they are unproven.

History
The original observation of the positive role played by certain bacteria was first introduced by Russian scientist and Nobel laureate Élie Metchnikoff, who in the beginning of the 20th century suggested that it would be possible to modify the gut flora and to replace harmful microbes with useful microbes. Metchnikoff, at that time a professor at the Pasteur Institute in Paris, produced the notion that the aging process results from the activity of putrefactive (proteolytic) microbes producing toxic substances in the large bowel. Proteolytic bacteria such as clostridia, which are part of the normal gut flora, produce toxic substances including phenols, indols and ammonia from the digestion of proteins. According to Metchnikoff these compounds were responsible for what he called "intestinal auto-intoxication", which caused the physical changes associated with old age.

It was at that time known that milk fermented with lactic-acid bacteria inhibits the growth of proteolytic bacteria because of the low pH produced by the fermentation of lactose. Metchnikoff had also observed that certain rural populations in Europe, for example in Bulgaria and the Russian steppes who lived largely on milk fermented by lactic-acid bacteria were exceptionally long lived. Based on these facts, Metchnikoff proposed that consumption of fermented milk would "seed" the intestine with harmless lactic-acid bacteria and decrease the intestinal pH and that this would suppress the growth of proteolytic bacteria. Metchnikoff himself introduced in his diet sour milk fermented with the bacteria he called "Bulgarian Bacillus" and found his health benefited. Friends in Paris soon followed his example and physicians began prescribing the sour milk diet for their patients.

Bifidobacteria were first isolated from a breast-fed infant by Henry Tissier who also worked at the Pasteur Institute. The isolated bacterium named Bacillus bifidus communis was later renamed to the genus Bifidobacterium. Tissier found that bifidobacteria are dominant in the gut flora of breast-fed babies and he observed clinical benefits from treating diarrhea in infants with bifidobacteria. The claimed effect was bifidobacterial displacement of proteolytic bacteria causing the disease.

During an outbreak of shigellosis in 1917, German professor Alfred Nissle isolated a strain of Escherichia coli from the feces of a soldier who was not affected by the disease. Methods of treating infectious diseases were needed at that time when antibiotics were not yet available, and Nissle used the Escherichia coli Nissle 1917 strain in acute gastrointestinal infectious salmonellosis and shigellosis.

In 1920, Rettger demonstrated that Metchnikoff's "Bulgarian Bacillus", later called Lactobacillus delbrueckii subsp. bulgaricus, could not live in the human intestine, and the fermented food phenomenon petered out. Metchnikoff's theory was disputable (at this stage), and people doubted his theory of longevity.

After Metchnikoff's death in 1916, the centre of activity moved to the United States. It was reasoned that bacteria originating from the gut were more likely to produce the desired effect in the gut, and in 1935 certain strains of Lactobacillus acidophilus were found to be very active when implanted in the human digestive tract. Trials were carried out using this organism, and encouraging results were obtained especially in the relief of chronic constipation.

The term "probiotics" was first introduced in 1953 by Werner Kollath (see Hamilton-Miller et al. 2003). Contrasting antibiotics, probiotics were defined as microbially derived factors that stimulate the growth of other microorganisms. In 1989, Roy Fuller suggested a definition of probiotics that has been widely used: "A live microbial feed supplement which beneficially affects the host animal by improving its intestinal microbial balance". Fuller's definition emphasizes the requirement of viability for probiotics and introduces the aspect of a beneficial effect on the host.

In the following decades, intestinal lactic acid bacterial species with alleged health beneficial properties have been introduced as probiotics, including Lactobacillus rhamnosus, Lactobacillus casei, and Lactobacillus johnsonii.

Preliminary research and potential effects
Experiments into the potential health effects of supplemental probiotics include the molecular biology and genomics of Lactobacillus in immune function, cancer, and antibiotic-associated diarrhea, travellers' diarrhea, pediatric diarrhea, inflammatory bowel disease and irritable bowel syndrome. Testing of a probiotic usually applies to a specific strain under study.

Diarrhea
Some probiotics have been shown in preliminary research to possibly treat various forms of gastroenteritis. They might reduce both the duration of illness and the frequency of stools. Fermented milk products (such as yogurt) also reduce the duration of symptoms. Antibiotic-associated diarrhea (AAD) results from an imbalance in the colonic microbiota caused by antibiotic therapy. Microbiota alteration changes carbohydrate metabolism with decreased short-chain fatty acid absorption and an osmotic diarrhea as a result. Another consequence of antibiotic therapy leading to diarrhea is overgrowth of potentially pathogenic organisms such as Clostridium difficile.
 * Antibiotic-associated

Probiotic treatment might reduce the incidence and severity of AAD as indicated in several meta-analyses. For example, treatment with probiotic formulations including Lactobacillus rhamnosus may reduce the risk of antibiotic-associated diarrhea, improve stool consistency during antibiotic therapy, and enhance the immune response after vaccination. However, further documentation of these findings through randomized, double blind, placebo-controlled trials are required to confirm specific effects and attain regulatory approval, which currently does not exist.

Potential efficacy of probiotic AAD prevention is dependent on the probiotic strain(s) used and on the dosage. Up to a 50% reduction of AAD occurrence has been found in preliminary studies. No side-effects have been reported in any of these studies. Caution should, however, be exercised when administering probiotic supplements to immunocompromised individuals or patients who have a compromised intestinal barrier.

Lactose intolerance
As lactic acid bacteria actively convert lactose into lactic acid, ingestion of certain active strains may help lactose intolerant individuals tolerate more lactose than they would have otherwise.

Colon cancer
In laboratory investigations, some strains of LAB (Lactobacillus bulgaricus) have demonstrated anti-mutagenic effects thought to be due to their ability to bind with heterocyclic amines, which are carcinogenic substances formed in cooked meat. Animal studies have demonstrated that some LAB have evidence for acting against colon cancer in rodents, though human data are inconclusive. Some human trials hypothesize that the strains tested may exert anti-carcinogenic effects by decreasing the activity of an enzyme called β-glucuronidase (which can generate carcinogens in the digestive system). Lower rates of colon cancer among higher consumers of fermented dairy products have been observed in one population study, but confirmation of such an effect does not exist.

Cholesterol
Animal studies have demonstrated the efficacy of a range of LAB to be able to lower serum cholesterol levels, presumably by breaking down bile in the gut, thus inhibiting its reabsorption (which enters the blood as cholesterol).

A meta-analysis that included five double blind trials examining the short term (2-8weeks) effects of probiotic yoghurt on serum cholesterol levels found a minor change of 8.5 mg/dL (0.22 mmol/L) (~4% decrease) in total cholesterol concentration, and a decrease of 7.7 mg/dL (0.2 mmol/L) (~5% decrease) in serum LDL concentration. A slightly longer study evaluating the effect of probiotic yoghurt on twenty-nine subjects over six months found no statistically significant differences in total serum cholesterol or LDL values. However, the study did note a significant increase in serum HDL from, 50 mg/dL (1.28 mmol/L) to 62 mg/dL (1.6 mmol/L) following treatment. This corresponds to a possible improvement of LDL/HDL ratio.

Studies specifically on hyper-lipidemic subjects are still needed.

Blood pressure
Although not a confirmed effect, some studies have indicated that consumption of milk fermented with various strains of LAB may result in modest reductions in blood pressure, an effect possibly related to the ACE inhibitor-like peptides produced during fermentation.

Immune function and infections
LAB may affect pathogens by means of competitive inhibition (i.e., by competing for growth) and there is evidence to suggest that they may improve immune function by increasing the number of IgA-producing plasma cells, increasing or improving phagocytosis as well as increasing the proportion of T lymphocytes and Natural Killer cells. Clinical trials have demonstrated that probiotics may decrease the incidence of respiratory tract infections and dental caries in children. LAB products might aid in the treatment of acute diarrhea, and possibly affect rotavirus infections in children and travelers' diarrhea in adults, but no products are approved for such indications.

A 2010 study suggested that antibiotics may turn the immune system "off" while probiotics turns it back on "idle", possibly more able to quickly react to new infections.

Helicobacter pylori
LAB may affect Helicobacter pylori infections (which cause peptic ulcers) in adults when used in combination with standard medical treatments, but there is no standard in medical practice or regulatory approval for such treatment.

Inflammation
LAB may modulate inflammatory and hypersensitivity responses, an observation thought to be at least in part due to the regulation of cytokine function. Clinical studies suggest that they can prevent reoccurrences of inflammatory bowel disease in adults, as well as improve milk allergies. They are not effective for treating eczema, a persistent skin inflammation. How probiotics may influence the immune system remains unclear, but a potential mechanism under research concerns the response of T lymphocytes to pro-inflammatory stimuli.

Bacterial growth under stress
In a study done to see the effects of stress on intestinal flora, rats that were fed probiotics had little occurrence of harmful bacteria latched onto their intestines compared to rats that were fed sterile water.

Irritable bowel syndrome and colitis
In one study, a commercial strain of bifidobacterium infantis improved some symptoms of irritable bowel syndrome in women. A separate small study showed that another probiotic bacterium, lactobacillus plantarum, may also be effective in reducing IBS symptoms. A study focused on bifidobacterium animalis showed a reduction in discomfort and bloating in individuals with constipation-predominant IBS, as well as helping to normalize stool frequency in said individuals. For maintenance of remission of ulcerative colitis, Mutaflor (E.coli Nissle 1917) randomized clinical studies showed equivalence of Mutaflor and mesalazine (5-ASAs).

Other
A study in 2004 testing the immune system of students given either milk or Actimel over a 6-week exam period (3 weeks of studying, 3 weeks of exams) tested 19 different biomarkers. Of these 19 biomarkers, only 2 were shown to be different between the two groups, increased production of lymphocytes, and increased production of CD56 cells. The tests were not blind and show that certain probiotic strains may have no overall effect on the immune system or on its ability.

A 2007 study at University College Cork in Ireland showed that a diet including milk fermented with Lactobacillus bacteria prevented Salmonella infection in pigs.

A 2007 clinical study at Imperial College London showed that preventive consumption of a commercially available probiotic drink containing L casei DN-114001, L bulgaricus, and S thermophilus can reduce the incidence of antibiotic-associated diarrhea and C difficile-associated diarrhea.

The efficacy and safety of a daily dose of Lactobacillus acidophilus CL1285 in affecting AAD was demonstrated in one study of hospitalized patients.

A 2011 study found that mice given Lactobacillus rhamnosus JB-1 showed lower levels of stress and anxiety than controls

Current research is focusing on the molecular biology and genomics of Lactobacillus and bifidobacteria. The application of modern whole genome approaches is providing insights into bifidobacterial evolution, while also revealing genetic functions that explain their presence in the particular ecological environment of the gastrointestinal tract.

Probiotics are used in industry to improve yields of pork and chicken production.

Factors affecting viability in foods
Some factors, both intrinsic and extrinsic, may influence the survival of probiotics in food, and so have to be considerated in all stages of probiotic food manufacturing.


 * physiological state of the added probiotic in the food
 * physicochemical conditions of food processing
 * physical conditions of product storage, like temperature
 * chemical composition of the product, such as content of nutrients, oxygen or pH
 * interactions with other product components, that can be inhibitory or protective

Physiological state
The physiological state of bacteria when prepared and remaining in a product itself are important factors for survival of the probiotics. Dryness in a food product keeps the bacteria in a relatively quiescent state during storage, while a wet product establishes potentially active metabolism. Temperature affects shelf life of the bacteria, with low temperature providing conditions for possible long term survival.

Bacteria can respond to stressful environments by the induction of various stress tolerance mechanisms. One of them is the induction of stress proteins by exposure of the cells to sublethal stresses so they can condition probiotics to better tolerate environmental stresses in food production, storage, and gastrointestinal transit. Different probiotic strains have their own intrinsic tolerances to environmental conditions, including how the culture is prepared, and some cross-protection can be observed, providing protection against other stresses by the exposure to only one stress. Stress responses can be explored to make probiotic strains more resilient and likely to survive in food matrices, with significant industrial importance.

Temperature
The temperature at which probiotic organisms grow is an important factor in food applications where fermentation is required, is also a critical factor influencing probiotic survival during manufacture and storage. As it is told above, the lower the temperature the more stable probiotic viability in the food product will be. During processing, temperatures over 45–50°C will be detrimental to probiotic survival, this means that the higher the temperature, the shorter the time period of exposure required to severely decrease the numbers of viable bacteria, ranging from hours or minutes at 45–55°C to seconds at higher temperatures. Therefore it is obvious that probiotics should be added downstream of heating/cooking/pasteurization processes in food manufacture to avoid the high temperatures. Elevated temperature also has a detrimental effect on stability during the product process of shipping and storage. Again, the cooler a product can be maintained, the better probiotic survival will be, like in vegetative probiotic cells in liquid products, where refrigerated storage is usually essential. If the product is dried, the bacteria will be in a quiescent state, so acceptable probiotic viability can be maintained in dry products stored at ambient temperatures for 12 months or more. Producing and maintaining low water activities in the foods is the key to maintaining probiotic viability during nonrefrigerated storage because there is a remarkable interaction between temperature and water activity.

pH
Some bacteria like Lactobacilli and bifidobacteria can tolerate lower pH levels because produce organic acid and products from carbohydrate metabolism. Indeed, numerous in vitro and in vivo studies have demonstrated that in gastric transit where the cells are exposed to low pH values and with a time of exposure relatively short, some probiotic organisms can survive. In fermented milks and yogurts with pH values between 3.7 and 4.3. lactobacilli are able to grow and survive, while Bifidobacteria tend to be less acid tolerant, with most species surviving poorly in fermented products at pH levels below 4.6. B. animales subsp. lactis is most commonly used in acidic foods because is more acid tolerant than human intestinal species, and B. thermoacidophilum, is even more tolerant to low pH (and heat), but has not yet been characterized thoroughly for probiotic traits and is not used commercially.

Regarding to fruit juices (pH 3.5–4.5) commercially successful products have been produced, such as Gefilus (Valio Ltd, Finland), which contains Lactobacillus rhamnosus GG. The viability at low pH can be improved with carriers such as dietary fibers. Survival of lactobacilli in low pHs has also been enhanced in the presence of metabolizable sugars, that allow cell membrane proton pumps to operate and prevent lowering of intracellular pH. This can improve survival during gastric transit, but may not be applicable to improving probiotic survival over the time stages of shelf-storage.

Water activity
For quiescent probiotic bacteria, water activity is a crucial determinant of survival in food products during storage. The higher moisture levels and water activity, the lower survival of probiotics. There is a substantial interaction between water activity and temperature with respect to their impact on the survival of quiescent probiotics. As the storage temperature is increased, the detrimental impact of moisture is magnified. Here, the osmotic stresses appear to play a role, with the presence of smaller molecules resulting in poorer bacterial survival, although the exact cell death mechanisms have not been elucidated yet.

There may be technological limitations to reducing water activity to low levels for improving survival. These include the energy costs of drying, adverse impacts on the taste of foods and difficulties in wetting and dispersing powders. Moisture barrier packaging may be applied to prevent the development of moisture from the environment during storage. Maintaining probiotic viability in moderate water activity foods (0.4–0.7) is a great challenge and solutions such as microencapsulation or incorporation of probiotics into fat phases of products can provide improved survival.

Oxygen
Both bifidobacteria and lactobacilli are considered strict anaerobes and oxygen can be detrimental to its growth and survival. However, the degree of oxygen sensitivity varies considerably between different species and strains, for example, lactobacilli, which are mostly microaerophilic, are more tolerant of oxygen than bifidobacteria, to the point where oxygen levels are not an important consideration in maintaining the survival of lactobacilli. Most probiotic bifidobacteria do not grow well in the presence of oxygen, although, many bifidobacteria have enzymatic mechanisms to limit the oxygen toxicity.

For oxygen sensitive strains, some strategies can be used to prevent oxygen toxicity in food products. Antioxidant ingredients have been shown to improve probiotic survival, as well as the use of oxygen barrier or modified-atmosphere packaging. Therefor, it is advisable to minimize processes that are highly aerating, particularly when using bifidobacteria.

Toxicity of ingredients
Interactions between probiotics and other ingredients could happen and those interactions can be protective, neutral, or detrimental to probiotic stability. Obviously, the inclusion of antimicrobial preservatives can inhibit probiotic survival and elevated levels of ingredients such as salt, organic acids, and nitrates can inhibit probiotics during storage, while starter cultures can sometimes inhibit the growth of probiotics during fermentation through the production of specific bacteriocins.

Growth factors, protective, and synergistic ingredients
Probiotic lactobacilli and, in particular, bifidobacteria are only weakly proteolytic and grow relatively slowly or poorly in milk. The growth of bifidobacteria can be improved by the presence of suitable companion cultures, which can aid in protein hydrolysis and through the production of growth factors. Some growth substrates such as carbon sources, nitrogen sources, and growth factors or antioxidants, minerals, and vitamins can be added to improve growth. Finally, the food matrix itself can be protective like in the cheese, where the anaerobic environment, high fat content and buffering capacity of the matrix helps to protect the probiotic cells both in the product and during intestinal transit.

Freeze–thawing
The damages made to cell membranes freezing probiotics is detrimental to survival, and also can make the cells more vulnerable to environmental stresses. To prevent or at least mitigate cell injury, protectants are usually added to cultures to be frozen or dried. Once frozen, probiotics can survive well over long shelf lives in products such as frozen yogurts and ice-cream. Using alternative methods of freezing, such as slow-cooling rates or pre-freezing stress, can significantly improve cell survival. Repeated freeze–thawing cycles are highly detrimental to cell survival and should be avoided.

Sheer forces
Probiotic lactobacilli and bifidobacteria are gram-positive bacteria with thick cell walls that are able to tolerate the sheer forces generated in most standard food production processes such as high-speed blending or homogenization, that may result in cell disruption and losses in viability.

Side-effects
In some situations, such as where the person consuming probiotics is critically ill, probiotics could be harmful. In a therapeutic clinical trial conducted by the Dutch Pancreatitis Study Group, the consumption of a mixture of six probiotic bacteria increased the death rate of patients with predicted severe acute pancreatitis.

In a clinical trial conducted at the University of Western Australia, aimed at showing the effectiveness of probiotics in reducing childhood allergies, researchers gave 178 children either a probiotic or a placebo for the first six months of their life. Those given the good bacteria were more likely to develop a sensitivity to allergens.

Some hospitals have reported treating lactobacillus septicaemia, which is a potentially fatal disease caused by the consumption of probiotics by people with lowered immune systems or who are already very ill.

There is no published evidence that probiotic supplements are able to replace the body's natural flora when these have been killed off; indeed bacterial levels in feces disappear within days when supplementation ceases.

Probiotics taken orally can be destroyed by the acidic conditions of the stomach. A number of micro-encapsulation techniques are being developed to address this problem.

Recent studies indicate that probiotic products such as yogurts could be a cause for obesity trends. However, this is contested as the link to obesity, and other health related issues with yogurt may link to its dairy and calorie attributes.

Some experts are skeptical on the efficacy of many strains and believe not all subjects will benefit from the use of probiotics.

Strains
Live probiotic cultures are available in fermented dairy products and probiotic fortified foods. However, tablets, capsules, powders and sachets containing the bacteria in freeze dried form are also available.

In the table below, only preliminary evidence exists for the health claims stated. Few of the strains presented have been sufficiently developed in basic and clinical research to warrant application for health claim status to a regulatory agency such as the Food and Drug Administration or European Food Safety Authority.

Some additional forms of yogurt bacteria include:
 * Lactobacillus bulgaricus
 * Streptococcus thermophilus
 * Lactobacillus bifidus - became new genus Bifidobacterium

Some fermented products containing similar lactic acid bacteria include:
 * Pickled vegetables
 * Fermented bean paste such as tempeh, miso and doenjang
 * Kefir
 * Buttermilk or Karnemelk
 * Kimchi undefined
 * Pao cai
 * Sauerkraut
 * Soy sauce
 * Zha cai

EFSA opinions of probiotics
The European Food Safety Authority has so far rejected claims on probiotics in Europe due to insufficient research and thus no conclusive proof. This includes:
 * Lactobacillus paracasei LMG P 22043 does not decrease potentially pathogenic gastro-intestinal microorganisms or reduce gastro-intestinal discomfort.
 * Lactobacillus johnsonii BFE 6128 . Immunity and skin claims all too general for consideration under the NHCR.
 * Lactobacillus fermentum ME-3 not shown to decrease potentially pathogenic gastro-intestinal microorganisms.
 * Lactobacillus plantarum BFE 1685. Immunity claim deemed too general for NHCR.
 * Bifidobacterium longum BB536 does not improve bowel regularity; does not resist cedar pollen allergens; does not decrease pathogens.
 * Bifidobacterium animalis ssp. lactis Bb-12 does not help maintain normal LDL-blood cholesterol; does not decrease pathogens or boost immunity.
 * Lactobacillus plantarum 299v does not reduce flatulence and bloating or protect DNA, proteins and lipids from oxidative damage.
 * Lactobacillus rhamnosus LB21 NCIMB 40564 does not help maintain individual intestinal microbiota in subjects receiving antibiotic treatment.

Multi-probiotic
Research is emerging on the potential health benefits of multiple probiotic strains as a health supplement as opposed to a single strain. The human gut is home to some 400-500 types of microbes. It is thought that this diverse environment may benefit from multiple probiotic strains; different strains populate different areas of the digestive tract, and studies are beginning to link different probiotic strains to specific health benefits.

Incomplete list of supplement products that contain more than one strain.