Role of Probiotics in Human and Animal Health Review

Probiotics as “Live microorganisms administered in adequate amounts, confer a health benefit on the host". The use of probiotics is not a new invention but in fact it exists in our traditional food such as preparation of Dahi, Yoghurt, Koumis, Leben, different types of cheese, beverages, alcoholic products etc., since time immemorial. Several scientists proved their role in disease prevention, improvement in feed control, increase in growth, production, raising of immune mechanism etc. Since that time the list of probiotics and their role in human, birds and animal health is increasing day by day. This article explores some of the important aspects in the role of probiotics in human and animal health.


Introduction
Food and Agriculture Organization (FAO) of the United Nations/ World Health Organization [1] defined Probiotics as "Live microorganisms which, when administered in adequate amounts, confer a health benefit on the host". The use of probiotics is not a new invention but in fact it exists in our traditional food such as preparation of Dahi, Yoghurt, Koumis, Leben, different types of cheese, beverages, alcoholic products, etc. since time immemorial. But Metchnikoff [2] at the Pasteur Institute first spotted the role of probiotics. He simplified his statement by correlating the ruminants' digestion which is carried out by microbes in the rumen. Tisser [3] long back more than a century ago pointed out that gut microbes from healthy breast fed infants were dominated by rods with bifids shaped (Bifidobacteria) than the formula fed infants, suffering with diarrhoea. Since that time the list of probiotics and their role in human, birds and animal health is increasing day by day.
The microbes used as Probiotics include bacteria, yeast or mold. The most common species of each are as:

Yeast and molds
Saccharomyces cerevisiae, Saccharomyces bourlardii, Aspergillus niger, Aspergillus oryzue, Candida pintolopesii, Sacaromyces boulardii. The type of the microbes used as Probiotics increasing due to the increase in the research in this field. Some of the beneficial role of probiotics consumption include

Role in competing with pathogenic bacteria
The probiotics maintain normal intestinal microbiota by competitive exclusion and antagonism. This role is exploited in maintaining health of man and animals or birds. The probiotic microbes attach to the intestinal epithelial lining of gut as a consequence pathogens are not allowed to attach and settled down in gut. This idea was exploited by Nurmi and Rantala [4] by applying probiotics in controlling severe outbreak of Salmonella infantis in Finnish broiler flocks. They administered probiotics and observed resistance to Salmonella infection. On the basis of this model number of probiotics were used in other studies that revealed encouraging results in terms of reduced colonization and shedding of Salmonella and Campylobacter infection [5].
Among the lactose fermenting bacterial probiotics like Lactobacillus species ferment the lactose and produce lactic acid which lowers pH of gut. So get environment becomes unfavourable for some pathogenic organisms to settle and multiply [6]. Dierick [7] reported that probiotics increase activity of intestinal enzymes and digestibility of nutrients. Similarly Schneitz [8] reported that use of Aspergillus oryzae increase digestibility of dry matter with the production of amylolitic and proteolytic enzymes. Adams et al. [9], Fanelli et al. [10,11] reported that probiotics may improve health status of birds by reducing ammonia production in intestines. O'Sullivan et al. [12] reported that probiotics change complex foods into simpler forms in body and they are able to complement many deficiencies in our digestive system such as production of vitamin K and absorption of certain ions.

Role in control of diseases
Lactobacillus as probiotic secrete vitamins 'B' , some essential aminoacids, enzymes that help in digestion. Lactobacillus salivarius produces high quantity of lactic acid can inhibit Helicobacter pylori so can prevent gastritis, peptic ulcers and gastric cancer in endemic areas of H. pylori can be prevented.
During the antibiotic therapy normal microflora are either killed or suppressed, encouraging the overgrowth of opportunistic or pathogenic strains. As a consequence mild to severe form of diarrhoea is caused. For instance cytotoxic strains of Clostridium difficile after antibiotic therapy damage the intestinal mucosa leading to diarrhoea, abdominal distension, vomiting, fever and leukocytosis. Hempel et al. [13] in a recent meta-analysis evaluated from the available evidence on probiotics for the prevention and treatment of antibiotic-associated diarrhoea and concluded that probiotic administration-(namely, L. rhamnosus, L. casei and the yeast S. boulardii) is associated with a reduced risk of the condition.

Role in control of Rotavirus
Treatment and prevention of infectious diarrhoea are probably the most widely accepted health benefits of probiotic microorganisms.
Rotavirus is the most common cause of acute infantile diarrhoea in the world and a significant cause of infant mortality. The virus replicates in the highly differentiated absorptive columnar cells of the small intestinal epithelium and the normal microflora seems to play an important role in the host response to the infection. In well-controlled clinical studies conducted by Isolauri et al. [14] and Szajewska and Mrukowicz [15] it was revealed that probiotics such as L. rhamnosus GG, L. reuteri, L. casei Shirota and B. animalis Bb12 can shorten the duration of acute rotavirus diarrhoea with the strongest evidence pointing to the effectiveness of L. rhamnosus GG and B. animalis Bb12. Several studies have investigated the efficacy of probiotics in the prevention of traveller's diarrhoea in adults, L. rhamnosus GG, S. boulardii, L. acidophilus, and B. bifidum exhibit significant efficacy [16]. In some studies it was found that probiotics produce bacteriocines which have inhibitory effect on enteropathogens [17].

Role in lactose intolerance
Lactose intolerance is a genetic defect due to deficiency of lactase enzyme resulting in the inability to hydrolyse lactose into the monosaccharides as glucose and galactose. So such deficient persons develop diarrhoea, abdominal discomfort and flatulence after consumption of milk or milk products when the bacterial enzymes ßgalactosidase degrade the undigested lactose in the bowel. Probiotics play a role in overcoming this problem. For instance if milk products like yoghurt are prepared with the help of S. thermophilus and L. delbrueckii ssp. Bulgaricus, because of higher ß-galactosidase activity lactose intolerance problem will be solved [18,19].

Role in inflammatory diseases
Probiotics enhance the immune system, synthesise and enhance the bioavailability of nutrients. Several investigators demonstrated the immune modulation effect on feeding probiotics to birds and other animal models characterized by secretion of IFNƴ, IL-2 etc. [20].
Isolauri et al. [21] observed an immune modulating effect of Lactobacillus rhamnosus GG in dietary antigens leading to secondary intestinal inflammation and disturbances.

Conclusion
There are number of scientific evidences that probiotics are useful in the prevention and treatment of certain conditions such as bowel disorders because of lactose intolerance, antibiotic associated diarrhoea and infectious diarrhoea and also in other disorders as allergy and stimulation of immune against some microbes, increase in growth performance. Consumer acceptance is increases day by day for the milk products having probiotics such as in India for Dahi and in other parts of globe Yoghurt. The food industry invests more on this growing market by development of new processes and products. So numbers of foods in the form of functional foods are coming up both for humans and animals or birds.