The intestinal microbiota is a complex ecological system composed of billions
of microorganisms in balance, mostly bacteria, which colonize the intestine and
work together for the health of the host, to promote the transit and absorption of nutrients.
Probiotics have to be distinguished from the more general category of live microbial cultures.
Probiotics belong to a niche group recognized as exhibiting certain characteristics that promote
survival in the human gastrointestinal tract, and provide a health benefit to the host.
The intestinal microbiota performs various functions in the body:
- Barrier against pathogen proliferation.
- Regulator of immune system maturation and response.
- Producer of vitamins (folic acid, vitamin K, group B vitamins).
- Regulator of the intestinal motility.
- Partial recoverer of energy from alimentary fibers.
Several factors can affect the balance of the intestinal microbiota, such as: unbalanced diet, seasonal or occasional diseases, chronic gastrointestinal diseases, antibiotic therapies, pharmacological treatment, ageing, and stress.
All of these factors can alter the balance of the intestinal microbiota and be responsible, therefore, for so-called dysbiosis.
Dysbiosis is a condition characterized by an alteration of the gut microbiota composition, in which the bacteria in the gut are out of balance and pathogenic (bad) bacteria begin to dominate, creating symptoms of digestive disturbance.
The main symptoms related to dysbiosis are: abdominal bloating, flatulence, change in bowel habits, abdominal pain, allergies, alterations in the immune system function, urinary tract infections and general discomfort.
In acute cases, this imbalance can result in the onset of diseases, such as inflammatory bowel disease and other gastrointestinal (GI) disorders, including gastritis, peptic ulcer disease, irritable bowel syndrome, and even gastric and colon cancer.
The modulation of the gut microbiota can be used to prevent or treat these conditions.
Changes in diet (including the use of prebiotics), antimicrobial-based intervention, faecal microbiota transplantation and especially probiotics, can represent valid options to rebalance the intestinal microbiota.
The term probiotic, derived from the Greek words “pro” (in favor of) and “bios” (life), refers to “friendly” bacteria, “live microorganisms that when administered in adequate amounts confer a health benefit on the host” (FAO/WHO definition).
Probiotics have to be distinguished from the more general category of live microbial cultures. Probiotics are not typically added to foods to provide a technological function, and are not used as starter cultures for yogurt- or cheese-making. Probiotics belong to a niche group recognized as exhibiting certain characteristics that promote survival in the human gastrointestinal tract, and provide a health benefit to the host.
Russian microbiologist Elie Metchnikoff (1845-1916) was the first to associate the large amounts of fermented dairy products with the good health and longevity of Bulgarians back in 1907. He proposed that the acid-producing organisms in fermented dairy products could prevent what he called "fouling" in the large intestine. He believed if eaten regularly, these foods could lead to a longer, healthier life.
Scientists have started to investigate specific probiotics strains and their potential benefits, as well as their role in the digestive tract. In the last decades, probiotics have been the subject of numerous studies worldwide.
At present, the methodological and ethical limitations of human studies still make it difficult to fully understand the mechanisms of action of probiotics, but some explanations are available.
In any case, benefits linked to the consumption of probiotic strains have already been suggested (e.g. helping to support the immune system and digestive health), and others are still being investigated.
The beneficial effects of probiotics on human health and nutrition are increasingly recognized by health professionals.
Numerous scientific studies on the properties and functionality of living micro-organisms have suggested that probiotics can play an important role in immunological, digestive and respiratory functions, and that they could have a significant effect on the alleviation of infectious diseases in adults and children.
In the human body, both good and bad bacteria live together. Under normal or "balanced" conditions, friendly bacteria in the gut outnumber the unfriendly ones.
Subsequently, probiotics can act as gut-beneficial bacteria that create a physical barrier against unfriendly bacteria.
Specifically, probiotics act to balance and reinforce the effects of the commensal flora with the following mechanisms:
At Pre-Epithelial Level
• Synthesis. Probiotics normalize and/or reinforce metabolite production of commensal flora.
• Direct antagonism. Probiotics secrete bioactive peptides with anti-microbic effect, bacteriokines, or proteases (serin protease) that antagonize or hydrolize toxins and adesins contrasting the virulence of pathogens.
• Exclusion of pathogens. Probiotics inhibit the access to the receptors by modifying the microenvironment.
At Epithelial Level
• Probiotics protect the epithelial barrier.
• Probiotics induce the expression of mucin and strengthen the mucosal layer.
At Post-Epithelial Level
• Modulation of the GALT (Gut Associated Lymphoid Tissue) immune system.
Probiotics affect and stabilize the composition of the microflora with an immunomodulating effect that increases innate and/or adaptative immune function and thus inhibits antigens and pathogens to initiate an immune response
Probiotics can also help offset the bacterial imbalance caused by taking antibiotics.
Antibiotics kill good bacteria along with the harmful ones, often leading to gas, cramping or diarrhea.
Potential benefits of probiotics have been seen in the treatment or prevention of symptoms such as diarrhea, constipation, bloating, abdominal pain, that are present in many conditions: irritable bowel syndrome, diverticular disease, SIBO (Small Intestinal Bacterial Overgrowth), Helicobacter pylor infection, Clostridium difficile infection, ulcerative colitis, and Crohn's disease.
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