Symbiosis – A Friendly Relationship between Man and Microbes


NKD Devi*, K Sujitha, BR Madhavi, BS Mrudula, MN Janaki and V Sri Ramya

KVSR.Siddhartha College of Pharmaceutical Sciences, Vijayawada-10.



A number of studies have been carried out on the effect of several beneficial microbes on treatment and prevention of several diseases. Generally microbes causes various diseases to humans, upon this there are some beneficial bacteria which can cure certain diseases. Some of the dietary supplements containing potentially beneficial bacteria or yeast, like probiotics are used to cure some diseases. These live-organisms after introducing into intestinal flora cannot survive for longtime. So in order to meet this problem prebiotics are included along with probiotics. These prebiotics are the non-digestible food ingredients that reach the colon intact, where they can be fermented preferentially by beneficial groups of bacteria.


As probiotics are mainly active in the small intestine and prebiotics are only effective in large intestine, the combination of the two may give a synergistic effect and this gives synbiotic product. Probiotics, prebiotics and symbiotic aimed at improving intestinal health currently represent the largest segment of the functional food market. These are also applicable for irritable bowel syndrome, prevents harmful bacterial growth, reducing inflammation, improving immune functions, lowering blood pressure, cholesterol lowering, prevention of colon cancer, managing lactose intolerance. Yogurt the oldest health promoting food is still widely used way to increase the number of advantageous bacteria in the intestinal tract. The most commonly used microbes are lactic acid producing bacteria such as lactobacilli and bifidobacteria belonging to the human normal microflora.The optimal strains should be developed further and introduced into the products for special functional properties and health outcomes.


Keywords: symbiosis, probiotics, prebiotics, yogurt, bifidobacterium



These micro organisms are of two types, harmful Micro organisms and beneficial Micro organisms. Harmful microbes cause diseases in man where as beneficial microbes are not harmful but causes several benefits to man. This can be also be explained by symbiotic relationship between man and microbes. Symbiotic relationship is a close ecological relationship between the individuals of two or more different species.   Sometimes a symbiotic relationship benefits both species, sometimes one species benefits at the other's expense, and in other cases neither species benefits. Example for this symbiotic relationship is gut of human and animals are a microbial ecosystem.


The upper bowel i.e., stomach, duodenum and jejunum have a large microbiota with up to 100000 colony-forming units /ml of contents. It has been further estimated that at least 500 different microbial species and 10-20 genera exists in human intestinal microbiota. Some of the symbiotic relationship between man and microbes can be explained in some of the products like Probiotics and Synbiotics.




Symbiotic relationship:

A symbiotic relationship is a relationship between two entities which is mutually beneficial for the participants of the relationship. Thus the two organisms are mutually beneficial for survival or other purposes.


There are many symbiotic relationships like Human - microbes, Humans- cultivated plants, Humans -intestinal bacteria, Vascular plants - fungi in mycorrhizae, Legumes- Rhizobia, Goby fish - shrimp, Cycads - Cyanobacteria etc.


The animal intestines contain large population of gut flora. In humans, these include species such as bacteroides, L-acidophilus and E. coli, among many others. Bacteria in the gut perform many important functions for humans, including breaking down and aiding in the absorption of otherwise indigestible food, stimulating cell growth, repressing the growth of harmful bacterial, training the immune system to respond only to pathogens, producing vitamin B12, and defending against some infectious diseases. Our intestinal tract is filled with an enormous number of helpful bacterial called probiotic bacteria. They are called probiotic bacteria because in term probiotic means “for life”.



Probiotics are dietary supplements containing potentially beneficial bacteria or yeast. According to the currently adopted definition by FAO/WHO, probiotics are “life micro organisms which when administered in adequate amounts confer a health benefit on the host” (1, 2).


LB17 probiotic lactic acid – 60


Lactic acid bacteria (LAB) are the most commonly used microbes. These microbes convert sugars and other carbohydrates into lactic acid. These microbes are mainly used in food industry.  Lactobacillus and bifidobacterium are the most widely used probiotic bacteria. These probiotic bacteria prevent gastro intestinal infections.


These probiotics strengthen the immune system to combat allergies, excessive alcohol intake, exposure to toxic substances and other diseases and protect gut flora in Human beings. The patients after a prolong use of Antibiotics or treatment for gut related candidacies are recommended to take probiotics. Maintenance of a healthy gut flora is however dependent on many factors like, quality and proportion of probiotic foods we take.


A. Natural probiotics:

Natural probiotics are the dietary supplements which are obtained directly from nature.These includes Sea weeds like Kombu, Hibamata from Norway, Brownalgae, Fucus and Medicinal herbs like Japanese ginseng and mushrooms like Agaricus brazei, Murill, Shiltake, Maitake and some vegetables,fruits and grins and cereals like Soya bean, unpolished rice.


In stomach the probiotic bacterial count is low due to high acidic pH. But when we come down in large intestine the count is more which aids in the digestion of the food and also keeps the harmful, disease causing micro organisms away (3). If the percentage of good bacteria is low when compared to bad bacteria, our body functions poorly and health problems increases gradually. For an adult, the average count of bacteria in intestinal tract is found to be 4 pounds where as in a healthy human being a balance of about 85% probiotic bacteria and 15% of harmful bacteria should be maintained.


B. Advantages of probiotics:

They are many benefits with these probiotics which are mentioned below.

1.                 Irritable bowel syndrome (IBS):

IBS is defined as a functional disorder in which abdominal pain is associated with a charge in bowel habit with features of disordered defecation and distention. IBS disturb intestinal flora and probiotics treatment may be effective in reducing IBS symptoms.Live lactobacillus acidophilus can be useful in the therapy of functional intestinal disorders. Apart from these single bacterial strain treatments, the bacterial mixture on IBS also acts effectively (4).


2.                 Managing Lactase Intolerance:

Lactose intolerance is the inability to digest significant amounts of lactose which is the major sugar found in milk and milk products. As lactic acid bacteria actively converts lactose into lactic acid. In practice probiotics are relatively low in lactase activity as compared to the yogurt bacteria which is normal. When certain active strains are ingested they may help lactose intolerant individuals tolerate more lactase. Lactobacillus bulgaricus produces acetaldehyde, which perfumes yogurt.


Lactobacillus Bulgaricus


3. Improving immune function and preventing infections:

Probiotic bacteria have beneficial effects on immune system of our body. By means competitive inhibition they protect against pathogens for example by increasing the number of IgA producing plasma cells, improving phagocytosis as well as increasing the ratio of T-lymphocytes and Natural killer cells.Probiotic nutrition management include mucosal vaccines immunomodulation, infection control and eradication of multidrug-resistant microbes, treatment of candidal vaginitis,prevention of transmission of AIDS and sexually transmitted diseases, cholesterol and blood pressure lowering, and antimutagenic activity . By many clinical trials they identified that probiotics decreases the infections of respiratory tract and dental infections in children. Lactic acid bacterial foods and their supplements showed in effectiveness in treatment and prevention of acute diarrohea (5).


4. Prevention of colon cancer:   Most human trials have found that the stains of probiotic bacteria tested may exert anticarcinogenic effect. They decrease the activity of enzyme B-glucoranidase. Short-lived metabolite mixtures isolated from milk that was fermented with strains of Lactobacillus bulgaricus and Streptococcus thermophilus are more effective in deactivating etiologic risk factors of colon carcinogenesis than are cellular components of microorganisms (6,7).


Streptococcus thermophilus


5.                    Cholesterol lowering:

The Probiotic bacterial has the efficacy to lower the serum cholesterol levels by breaking down bile in the gut and inhibiting its reabsorption. Specific lactic acid bacteria reduce the total and LDL cholesterol levels. The lactobacilli lower cholesterol by assimilating it thus protecting from occurrence of atherosclerosis of the brain and cardio-vascular system. Cholesterol is also lowered by the changed hydrolase’s enzyme activity (8,9). Lactobacillus changes bile salts in your gut into bile acids. This change inhibits the emulsified form of cholesterol, keeping a substantial amount from being absorbed. The unabsorbed cholesterol is eliminated in the feces.


6.  Urinary tract infections:

The probiotics are also used to reduce the urinary tract infections. They may have other health benefits as well. The best-known probiotics are the lactobacilli strains, such as acidophilus, which is found in yogurt and other fermented milk products. The probiotics bifidobacteria and GG lactobacilli may prove to be even more important. Other probiotics include the lactobacilli rhamnosus, casel, plantarium, bulgaricus, and salivarius, and also Enterococcus faecium and Streptococcus thermophilus.

Lactobacilli have the potential to help protect women from UTIs by means of maintaining a low pH environment, hindering E.coli growth and by producing hydrogen peroxide which in turn produces an environmental hostile for bacteria (10,11).


7. Prevents Harmful Bacterial growth:

These probiotics are also used to prevent harmful intestinal flora. This can be proved by seeing the effects of stress on intestinal flora, when rats were fed probiotics had little occurrence of harmful bacterial when compared to rats that were fed sterile water.


8. Intestinal Flora in Infants:

Breast-feeding infants protects them from infections disease. There is a lot of differences between intestinal floral of breast – feeding infants and bottle feeding infants. Some factors in breast milk that may enhance the selective growth of bifidobacteria include the presence of N-acetyl glucosamine, glucose, lacto ferrin, galactose, and fracture. Breast – feeding can also affect the occurrence and virulence of colonizing pathogens.


9. Prevention of diarrhoeal disease:

The regular consumption of specific probiotic agents over extended periods of time was showed to decrease the incidence of acute diarrhoea in several well designed trials. Lactobacillus rhamnosus GG has consistently reduced the duration of rotavirus-associated diarrhoea in randomized controlled trails. Lactobacillus reuteri, Bifidobacterium lactisBb-12and Saccharomyces boulardii have also shortened the duration and decreases the symptoms associated with acute viral diarrhoea.   Antibiotics can severely disrupt gut microbial ecology. Ingestion of probiotics with a prescribed antibiotic can reduce the effect of such microbial alteration and may resulting changes in stool consistency and frequency.


10. Food allergies and atopic diseases:

Several recent studies have suggested a role for gut-colonizing bacteria in preventing and treating manifestation of food allergy and atopic diseases, including atopic eczema, asthma, and other allergies. It has been proposed that children developing allergy may have an aberrant gut microbiota. Lactobacillus GG was effective in prevention of early atopic disease in children at high risk. Probiotic bacteria are administered to a pregnant woman at least two weeks before infant delivery and after delivery, probiotic bacteria are administered to the newborn infant for at least two months. The amount of probiotic bacteria administered is about 1×108 to about 1×1010 colony forming units of the probiotic bacteria.


11. Probiotics in Aquaculture:

Researchers are trying to use probiotic bacteria in aquaculture to improve water quality by balancing bacterial population in water and reducing pathogenic bacterial load. Researchers are increasingly paying more attention to this new approach and have made considerable headway.

C. Applications of probiotics:




A nondigestible food ingredient that beneficially affects the host by selectively stimulating the growth and activate a limited number of bacteria in the colon.


Examples of Prebiotic Sugars:

Fructooligosaccharides (insulin, FOS etc), Soy oligosaccharides, Galactooligosaccharides (GOS), Lactulose,Raffinose,Lactosucrose,IsomaltooligosaccharidesSoyabeanoligosaccharides, Xylo-oligosaccharides


Prebiotics that feed the beneficial bacteria in the gut mostly come from carbohydrate fibers called oligosaccharides. These are not digested in our body, so the oligosaccharides remain in the digestive tract and stimulate the growth of beneficial bacteria. Sources of oligosaccharides include fruits, legumes, and whole grains. Fructo-oligosaccharides may be taken as a supplement or added to foods. Yogurt made with bifidobacteria contains oligosaccharides. Study of the fermentation of individual oligomers included that Lactobacillus plantarum and Lactobacillus rhamnosus were only capable of metabolizing the trisaccharide and tetrasacchariede fractions, pentasaccharides were not metabolized by these strains. Fractionated GOS were used as growth substrate for Bacillus lactis and for L.rhamnosus.The largest increase in bifidobacteria was seen on xylo-oligosaccharide and lactulose, the largest increase in lactobacilli was on FOS.



Symbiotic is a supplement that contains both a prebiotic and a probiotic that work together to improve the “Friendly Flora” of the human intestine. A symbiotic product containing one to ten billion active cells. A symbiotic product should be considered a “functional food”, rather than some chemistry formulations.


Examples of Synbiotics:

1) Bifidobacteria + FOS

2) Lactobacilli + lactitol

3) Bifidobacteria + GOS

Fermented milk like yogurt and kefir are considered to be true symbiotic products, that is functional foods since they supply the live bacterial and the food they need to survive. The best symbiotic combinations currently available include bifidobacteria and fructo-oligosacchorides (FOS).

The main reason for using a symbiotic is that a true probiotic, without its        prebiotic food, does not survive well in the digestive system. In cases where antibiotics have been taken, it is sometimes suggested that such a product should be taken several times a day, preferably at least 30 minutes before meals.


A.                   Major characteristics Symbiotics:

They have anti microbial, anti carcinogenic, anti diarrheal, anti allergic qualities. They helps in osteoporosis prevention, reduction of serum fats and blood sugar,regulates  the immune system and also treats live-related brain dysfunction.


B. Digestion of symbiotics:

A symbiotic depends directly on the various probiotic lacterias ability to survive digestive juices as well as the alkaline environment of the duodenum. Prebiotics are necessary to assist the probiotic since probiotic sugars are not digested.This enables prebiotics to travel through the digestive tract and feed the bacteria in the intestines. These sugars are then fermented by bifidobacteria, lactobacilli, and other in the colon to produce some beneficial by-products like Short chain fatty acids acetate, propionate and butyrate, Hydrogen, hydrogen sulfide, carbon, Lactate, pyruvate, succinate and formate.


C. Symbiotic products:

Yogurt is a dairy product produced by bacterial fermentation of milk. This fermentation of lactose produces lactic acid, which acts on milk protein to give yoghurt. Soy yogurt, a dairy yogurt alternative is made from soy milk. The product is rich in protein, calcium, riboflavin, vitamin B6 and Vitamin B12.


Nutrition value per 100 gm energy 60 Kcal of Yogurt contains Carbohydrates - 4.7 g, Fats-3.3 g, Proteins -3.5 g, Riboflavin-14 g, Calcium-121 m.g

Lactose content diminishes during storage.


D. Culture of Yogurt:

Yogurt is made by introducing specific bacteria. Strains into milk, which is fermented under controlled temperatures and environmental conditions. The bacteria ingested into natural milk releases lactic acid as a waste product. The increased acidity also prevents the growth of pathogenic bacteria. This yoghurt consists of different organisms like streptococcus salivarius and Lactobacillus delibrueckii. Often these two are co-cultured with other bacteria like Lactobacillus casei and bifidobacterium species for taste and health (12).


E. Bifidobacterium:

Bifidobacterium is a genus of gram positive prokaryotes, non-motile often branched anaerobic bacteria that reside in the colon. 28 species of bifidobacteria have been isolated from the intestines of humans and animals. Bifidobacteria aid in digestion, are associated with a lower incidence of allergies and also prevents some forms of tumor growth. Some are used in probiotics.


F. Growth factors of bifidobacteria:

The growth factors include human milk components of N-acetyl glucosamine containing oligosaccharides, enzymatic cleavage products of proteins, glycoprotein and pantethine compounds. Oligosaccharides such as lactulose as well as dietary fibers have been found to be effective in promoting intestinal growth of bifidobacteria. These oligosaccharides are indigestible in the human digestive tract and reach the large intestine and they are utilized by bifidobacteria. The bifidobacteria proportion increases with the daily consumption of lactulose, and decrease when lactulose consumption is stopped. Other faecal ammonia and putrefactive substances are suppressed by taking lactulose. This lactulose is used as a treatment for portal systemic encephalopathy and also for alleviating constipation.



This bifidobacteria are widely applied in foods, medicine and animal feeds to improve the intestinal microflora.

Ø     The digestive and intestinal functions encouraged a better protection against gastrointestinal disturbances.

Ø     Re-balancing of the faecal flora also guarantees a normal uremia, and a low ammonia concentration in Improvement of intestinal content.

Ø     Bifidobacteria ferment non-digestible carbohydrates into lactate and acetate, which lowers the pH of the intestinal medium. As a result the absorption of protonated amines is reduced and the proliferation of other harmful bacteria is reduced or even inhibited.

Ø     Bifidobacteria may reduce the risk of colon cancer. It helped to inhibit the formation of aberrant crypt foci which are preneoplastic lesions increasing the risk for future development of adenomas and carcinomas.

Ø     Bifidobacteria helps to activate the immune system. It produces substances that are able to activate the immune system of the host. This allows a better defence against microflora infections and against tumorigenesis.

Ø     Bifidobacteria helps to synthesize certain vitamins. Mainly those of the B-group, and of proteolytic enzymes which act among others, on casein and lysozyme.

Ø     Bifidobacteria reduces the production of putrefactive components. Bifidobacteria are characterized by a low production of ammonia, aliphatic amines and H2S, usual products of putrefaction. They also lower the production of nitrites which, with amines, are the substrates for the synthesis of nitrosamines, some of which are powerful carcinogens.

Ø     Bifidobacteria increases the absorption of minerals. Bifidobacteria induce a better resorption of some ions such as iron and calcium.



By the study of this symbiotic relationship between man and microbes we can conclude that, microbes with health impact will remain an important functional ingredient also in the future. Along with the advantages over curing diseases, there is little doubt that probiotics particularly Lactobacillus GG, are effective in viral diarrhoea illness. The non pathogenic organisms used as probiotics, consist of a wide variety of species and sub-species, and the ability to adhere, colonise and modulate the human gastrointestinal system is not a universal property. Future research must investigate the mechanisms by which gut microflora interacts with intestinal epithelium in health and disease. With this knowledge optimal strains of probiotic may be developed. It is likely that in future we will see a much more rational usage of prebiotics and symbiotics targeted towards those cases where they are most needed.



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Received on 26.01.2010

Accepted on 12.02.2010        

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Research J.  Science and Tech.  2(1):Jan. – Feb. 2010: 01-07