5. Prebiotics, probiotics & the human intestinal microbiota Flashcards
Microbiota vs Microbiome
Microbiota – microbial organisms that live on or in the human body
Microbiome – collective genomes of all the microbes in the microbiota
Human intestinal microbiota [1]
- Humans colonised by many micro-organisms, residing on or in various organs, including the skin & GIT
- Hundreds of species of bacteria are present in the human gut, many of which are beneficial for the host – balance of these micro-organisms are require for normal GI function
- Regulator of host metabolic & immune functions
- Protects against invasive pathogens e.g. Clostridium difficile (colonisation resistance)
- Associations between specific characterisation of intestinal (& other body site) microbiota & certain human disease conditions are being explored
Human intestinal microbiota [2]
Can be altered by e.g.
- Dietary shifts
- Medicines (immunosuppressants, antibiotics)
- Results in dysbiosis (alterations in the microbiota)
- For some individuals, recovery from disturbance may take > 6 months
Human intestinal microbiota [3]
Implications not full understood:
- Is disease (e.g. IBD) due to microbial community disturbance?
- How can the microbial community disruption on colonisation resistance e.g. against Salmonella?
- Dysbiosis can lead to overgrowth of many pathogenic bacteria esp. C. difficile
- CDAD (C. difficile-associated diarrhoea) in particular is associated with serious adverse events, including electrolyte disturbances, volume depletion, pseudomembranous colitis, toxic megacolon & in rare cases, death
Prebiotics [1]
- Non-digestible food ingredients that beneficially affect the host through stimulating growth &/or activity of certain ‘beneficial’ bacteria in the colon of the GI tract
- E.g. Fructo-oligosaccharides (FOS), galacto-oligosaccharides (GOS), inulins (NB: not insulin), lactulose (galactose + fructose)
- Inulins are polysaccharides comprising mostly fructose units (20 to 1000s) & usually with a terminal glucose unit
+ Short chain inulins sometimes called FOS - Inulins are naturally occurring carbohydrates produced & stored by many plants & used by them as an energy source
- Inulins/FOS (aka oligosaccharide fructans) occur naturally in some plants, particularly some fruits (e.g. bananas) & vegetables (e.g. onions, garlic, asparagus, leeks, chicory, Jerusalem artichoke
Prebiotics [2]
- Inulin(s)/FOS are not digested by enzymes in the upper GIT – FOS can resist hydrolysis by salivary & intestinal digestive enzymes because of the configuration of their glycosidic bonds
- They reach the colon intact, where they are metabolised by bacteria, producing lactic acid – reduces pH which favours growth of ‘beneficial’ bacteria
- In clinical studies, ingestion of fructo-oligosaccharides increased the relative proportion of Bifidobacteria species & reduced the concentration of ‘harmful’ bacteria (e.g. Clostridia spp) in faeces
- So, there is evidence that prebiotics can modify the composition of the microflora in the colon, &/or effect some metabolic activities of the microflora
- But, currently little evidence that leads to beneficial health outcomes
Probiotics [1]
- Live preparations of some types of ‘beneficial’, non-pathogenic micro-organisms (mainly bacteria or yeast), intended to normalise imbalances in host’s microflora & replace ‘harmful’ bacteria in the gut
- “live microorganisms that, when administered in adequate amounts, confer a health benefit on the host”
Key elements:
- Microbial
- Viable
- Beneficial to health (or intended to be so)
Probiotics [2]
Bacteria – numerous species used:
- Lactobacillus species e.g. L. acidophilus, L. casei, L. fermentum, L. gasseri, L. johnsonii, L. paracasei, L. plantarum, L. rhamnosus, L. salivarius; part of lactic acid bacteria group; Gp+ve, acid-resistant
- Some Bifidobacteria spp., e.g. B. adolescentis, B. animalis, B. bifidum, B. breve, B. longum
- Streptococcus salivarius subsp. thermophilus, Enterococcus faecium
Yeast – microscopic fungi:
- Saccharomyces boulardii, Saccharomyces cerevisiae
Probiotics [4]
-Typically, probiotic products comprise combinations of ~5 – 15+ different micro-organisms (species/strains of the same species)
- E.g. Proprietary probiotic blend providing 50 billion CFU (CFU = colon-forming units), each ampoule contains:
+ Lactobacillus acidophilus (strain ATCC-SD5221) 10 billion CFU
+ Lactobacillus paracasei (strain Lpc-37) 10 billion CFU;
+ Bifidobacterium lactis (strain Bl-07) 10 billion CFU;
o Bifidobacterium lactis (strain Bl-04) 9 billion CFU;
+ Bifidobacterium bifidum (strain Bb-02) 1 billion CFU etc
- Strain – genetic variant/subtype of species
+ Different strains can have different properties/characteristics e.g. adhesion, resistance
- Sometimes in combination with other ingredients e.g. vitamins, minerals, herbal ingredients e.g. cranberry fruit extract
Probiotics [4]: Quality
Wide variation in context/number of viable cells – expressed as CFU across different products
Depending on species, strain, indication, user, 1bn – 40bm CFU/d
- Usually 5+bm CFU/day – evidence is strain specific
- Actual contents differ from label e.g. contain fewer cells
- Misspelling of names of bacterial species/strains or incorrect names
- Similar issues with veterinary probiotics
USP standards:
- USP has developed & published monographs of probiotic strains in the Food Chemical Codex (FCC) – submissions for other microbial strains are in progress
- Monographs include description/definition, standards for identification, assay method & acceptance criteria, limits for contaminants, labelling, packaging & storage
To refrigerate or not refrigerate:
- Many bacterial species contained in probiotic products are sensitive to heat & moisture
- Some organisms killed by heat, moisture, encourages growth, but organisms subsequently die due to lack of nutrients & environment
- Freeze-dried, blister packed probiotics generally do not need to be refrigerated or kept in low humidity environments, but should not be exposed above room temperature
- Care with ordering products online/mail order
Probiotics [5]
- Live organisms present in some fermented milk products e.g. yoghurt, but may not be well-defined in terms of strain composition & stability, require refrigeration
- Expert panels recommend that such foods are best described as “containing live & active cultures”, but should not be called probiotic
Probiotics [6]: Claims (7)
- “Super probiotic designed to restore & correct stomach bacteria”
- “Aids in maintaining a normal healthy immune system”
- “Helps maintain normal healthy urogenital flora”
- “Helps reduce the symptoms of medically diagnosed IBS”
- “Helps maintain normal bowel function”
- “Support to relieve diarrhoea”
- “Support for preventing gastric problems”
Probiotics [7]: Claims/marketed uses (7)
- Supporting a healthy gut microbiota (not yet scientifically defined in terms of microbial composition)
- Restoring a healthy gut microbiota after antibiotic treatment
- Enhancing the immune system
- Prevention & treatment of diarrhoea, including ‘traveller’s diarrhoea’, antibiotic-treatment-associated diarrhoea, acute diarrhoea
- Prevention & treatment of vaginal & UTIs
- Prevention & treatment of allergic conditions
- Treatment of inflammatory bowel conditions, e.g. IBS, ulcerative colitis, Crohn’s disease
Probiotics [8]: How might they work? (6)
Possible modes of action for probiotics include:
- Aid maintenance of community of beneficial microorganisms
- Help restore beneficial bacteria after disruption (e.g. with antibiotic treatment)
- Stabilise GIT’s barriers against ‘bad bacteria’, or produce substances that inhibit growth of ‘bad bacteria’
- Outcompete undesirable microorganisms, e.g. for nutrients
- Stimulate the immune response
NB:
- Probiotics may act in several ways
- Different probiotics may act in different ways
Probiotics [9]: Evidence - caveats
Consider the following when reviewing clinical evidence for probiotics:
- Few studies undertook pharmaceutical analysis of the product/material to confirm identity, viability, quantify contents, checks for presence/absence of contaminants
- Many studies have methodological limitations, which means that the results have to be interpreted cautiously - Evidence is strain-specific – results of one study should not be extrapolated to products containing other strains/species
- More research needed on effects of specific strains, species, dose regimen etc
- Also, any new trials since Cochrane review, other systematic reviews
