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Probiotics is an interesting new subject in microbiology. Recent commercials praise the digestive benefits of yogurts; but why and how could yogurt help with digestion? The answer is probiotics. This paper is about probiotics and their benefits, with a main focus on the Gastrointestinal(GI) tract. In this paper I plan to answer the following questions; What are probiotics? Where do they live? How do they work? How do they help us? How do you get probiotics into your body? What are some challenges for probiotics? What ailments can probiotics help with? What harmful side effects are associated with probiotics?
What are probiotics?
The first hint we get is from the name itself. It is easy to see the roots "pro" and "bio". Put these two together and we get "for life"(5). This is a very fitting name because probiotics are defined as "living microorganisms which, when administered in adequate amounts, confer a health benefit on the host (6) " or "live nonpathogenic microorganisms administered to improve microbial balance, particularly in the gastrointestinal tract (10)". The idea of probiotics dates back to 1908. A Nobel Prize winner named Eli Metchnikoff suggested that the long lives of Bulganin peasants may be attributed to their intake of fermented milk products (5). Probiotics are mainly strains of bacteria or yeast. The two most widely used probiotics are Lactobacillus and Bifidobacterium. Both of these are lactic acid bacteria. Saccharomyces boulardii is an example of a yeast probiotic. Since there are so many types of probiotics it is impossible to make generalizations on the health benefits of probiotics as a whole. In other words, what is beneficial about one strain may not hold true for another strain (10). With that being said there are six criteria that a microorganism should have to be considered a probiotic.
"i) It should be isolated from the same species as its intended host;
ii) It should have a demonstrable beneficial effect on the host,
iii) It should be non-pathogenic nontoxic, and free of significant adverse side effects;
iv) It should be able to survive through the gastrointestinal tract,
v) It should be stable during the intended shelf life and contain an adequate number of viable cells to confer health benefit and
vi) It should be compatible with product format to maintain desired sensory properties; and label accurately (1)"
What is their Environment?
To understand how probiotics work you first need to understand the environment in which they live. Most probiotics are taken orally. This makes the GI tract the primary target for probiotics. Right after birth an infant's intestinal tract is sterile. Microbes soon start to colonize different regions of the gut (3). An adult GI tract is home to billions of microorganisms with thousands of species. This is collectively known as the intestinal microbiota, also known as gut flora or intestinal microflora (4). The human body and the microbiota have a symbiotic relationship. The human host provides nutrients and a body to live in. The microbiota in turn helps us in many ways also. It prevents growth of harmful microorganisms, produces and helps our body absorb vitamins, and trains our immune system (4). It is important that this environment maintains a balance. Things like "antibiotics, immunosuppressive medications, surgery, and irradiation (10)" can disrupt this balance. This is where probiotics come in.
How do they help/work?
Probiotics can help maintain and enhance the balance of the microbiota. Lactobacillus and Bifidobacterium produce lactic acid, acetic acid, and propionic acid. These acids will lower the pH in the intestines. This helps suppress the growth of pathogenic bacteria, thus helping maintain and/or reestablish microbiota homeostasis (10). Bacterial probiotics can also produce substances that are toxic to pathogenic microorganisms. Examples of these substances are hydrogen peroxide, organic acids, bacteriocins, and biosurfactants. A stain of Lactobacillus GG can produce a "low-molecular-weight compound that inhibits a broad spectrum of gram-positive, gram-negative and anaerobic bacteria (10).
Another way that probiotics help is by maintaining the mucosal epithelial surfaces that cover the GI tract. These surfaces can serve as entry site for pathogens (6). The GI epithelium, with the help of indigenous microbiota, creates a physical and chemical barrier against pathogens. This is known as colonization resistance. "The rational behind colonization resistance is the ability of normal microbiota to occupy the same ecological niche as pathogenic organisms (6)." In other words, it's similar to competitive inhibition. The microbiota takes nutrients and adhesion sites on the mucosa that would otherwise be used by pathogens. It is thought that this is how Lactobacillus is able to block pathogens like E. coli, Klebsiella pneumoniae, and Pseudomaonas aerginosa (10).
How do you get probiotics into your body?
Probiotics are regulated as dietary supplements and food. Supplements can come in capsules, tablets and powders (9). They are also in foods, mainly those that contain lactic acid. Foods in this category consist of fermented milks, cheeses, fruit juices, wine, and sausages (5). They are also in miso, tempeh, juices and soy beverages (9).
What are some challenges for probiotics?
Earlier when stating the six criteria for being a probiotic, we briefly touched on some of the challenges that face probiotics. Probiotics are taken orally. They have to be able to survive the conditions of the stomach and intestines. This means being resistant to bile, hydrochloric acid, and pancreatic juice (5). Then after that they have to "colonize and reproduce in the gut, attach and adhere to the intestinal epithelium and stabilize the balance of the gut flora (10)." This is a process that many microorganisms have difficulty with. To help them there is something called "microencapsulation".
"Mircoencapsulation is a process in which cells are immobilized within an encapsulation matrix. The encapsulation material should retain the bacteria and should also restrict the movement of acid and digestive enzymes though the microcapsules. The capsule should also be able to maintain its integrity during passage though the gastrointestinal tract until it reaches its target destination, where the capsule should break down and release the probiotic bacteria (2)." In other words, if the bacteria can not survive the trip, there is then a process in which they can put a protective capsule around themselves. The coating it self has to be nontoxic and readily available (2).
Another challenge for probiotics is antibiotics which not only kill bad bacteria but also good bacteria. If the good bacteria is not present than harmful bacteria can colonize (4).
What ailments can probiotics help with?
There are many ailments that probiotics may alleviate but for the focus of the paper, I'm going to only focus on those that show the most promise. This is the group of GI ailments including inflammatory bowel disease (IBD), irritable bowels syndrome (IBS), and diarrhea.
IBD is a disease of the digestive track. This includes diseases like ulcerative colitis, Crohn's disease and pouchitis(10). Mice administered with Lactobacillus and Bifidobacterium prior to the induction of colitis maintain the higher levels of Bacteroides (the major anaerobic bacteria of the colon) compared to that of the control (7). Also probiotics have been shown to strengthen the mucosal barrier and reduce inflammation (7).
IBS is "characterized by abdominal pain, bloating, flatulence and altered bowel habits. These symptoms may be due to bacterial overgrowth in the small intestine, causing increased fermentation activities and gas production (10)." One third of all visits to gastroenterologists are due to IBS and it is the most frequent functional gastrointestinal disorder (8). An analysis of 20 trails on probiotics (mostly Lactobacilli and Bifidobacteria) found that they improve symptoms of IBS and helped abdominal pain when compare to that of a placebo (10).
Probiotics can also help with many types diarrhea. This includes Rota virus diarrhea, Antibiotic associated diarrhea (AAD), Radiation induced diarrhea, and Traveler's diarrhea (5).
What are some harmful side effects risks involved with probiotics?
Probiotics may cause bloating or flatulence (10). Lactobacilli and Bifidobacteria are thought to be non-pathogenic or to have a low possibility of being pathogenic. Most of the time this is true but in some cases they may act as pathogens. This is mainly in immunocompromised patients. They can cause bateraemia and sepsis (6). It is also not recommended for people suffering from acute pancreatitis (9).
In a randomized, double blind, placebo-controlled, crossover trial, 16 subjects suffering from IBS took one capsule of 10^10 CFU Lactobacillus platarum MF 1298 or placebo. This was for two, three-week periods separated by a four week wash out period. The result was that the test subjects preferred the placebo to the probiotic. The group that took Lactobacillus platarum had higher scores for diarrhea, constipation, and alternating bowel movements (8). This goes to show that science can not make sweeping generalizations about the genus of probiotics. Each species may have its own benefits and/or draw backs.
One thing to take into consideration; "at least 60% of the bacteria in the human large intestine remain uncultured and unknown, it is not yet possible to define the ideal balance of micro-organisms in the intestine (3)." The study of probiotics is relatively new. It is good to stay a little skeptical, but probiotics do seem to have some promise. Probiotics can help restore a body's natural balance and can even be used to maintain our current state of health. From almost the point of birth to our death bed they will be with us. It's strange to think that something so small could play such a huge role in our lives and health. If we take care of our microorganisms, then they should also take care of us.