Gut microbiota and Immunity Flashcards
Identify the main levels of gut defense, giving examples.
1) Physical (e.g. skin, mucosa, secretions)
2) Innate immunity
3) Acquired immunity (antibodies)
Identify the main host defenses in the mouth.
- Flow of liquids (flushes bacteria)
- Saliva (contains antimicrobials + growth factors which aid wound healing and therefore help protect mucosa)
- Antimicrobials (lysozymes, lactoferrin, IgA, sIgA, peroxidase)
- Microbiota
Identify the main host defenses in the esophagus.
- Flow of liquids
- Peristalsis (pushes bacteria out)
Identify the main host defenses in the stomach.
- Acid pH (1 or 2, produced by parietal cells)
- Antimicrobials (beta defensins)
- Mucus (protects us against acid + prevents bacteria from easy attachment)
Identify the only bacteria that lives in the stomach.
Helicobacter Pylori
Define hypochloridia and achloridia. How are these significant wrt gut immunity ?
Less production of acid
No production of acid
They predispose to infection
Identify the main host defenses in the small intestine.
- Flow of gut contents
- Peristalsis
- Mucus
- Bile (acidic)
- Secretory IgA (main agent of mucosa immunity, only immunoglobulin that passes through mucosa membranes)
- Antimicrobial peptides (lysozymes, alpha defensins, beta defensins)
- Microbiota
Are alpha defensins found in the stomach ?
No, only small intestine
Identify the main host defenses in the large intestine.
- Peristalsis
- Mucus
- Microbiota
- Shedding and replication of epithelium (if damaged or infected, we want to get rid of it)
Identify the different possible types of host-bacteria relationships.
- Commensal (bacterium benefits, host neither harmed nor benefits)
- Symbiotic (both benefit)
- Parasitic (bacterium benefits, other is harmed)
Can bacteria in commensal/symbiotic relationships become parasitic ?
Yes, under the right conditions
Define probiotics.
“Live bacteria and yeasts that also called “the good” microorganisms because they benefit the the digestive system.”
Identify examples of probiotics.
Lactobacillus spp.
Bifidobacterium spp.
Bacteroids spp.
Identify ways in which probiotics ‘benefit’ the digestive system.
- Produce lactic acid (acidic conditions unfavorable to most bacteria)
- Produce bacteriocins (antimicrobial peptides)
These allow them to adhere to colonise areas instead of potentially harmful bacteria.
Define prebiotics.
Non-digestible food ingredients (especially carbs) which stimulate growth and activity of gut microbiota (not digested by stomach acid, so gets through to intestines).
Identify all the ways in which probiotics and prebiotics help gut immunity.
1) Development of mucosa barrier
2) Synthesis of vitamins (K, B12, folic)
3) Metabolism of bile acids
4) Production of short chain fatty acids (which bacteria love)
5) Reduction in pH in large bowel
6) Immune system activation
Describe the distribution of normal microbiota throughout the gut.
Large bowel has highest density of microbiota
- Lactobacilli is present in stomach, duodenum, large intestine,
- Bifidobacteria is present in large intestine and fecal material
- Bacterioid spp is present in jejunum/ileum, large intestine, fecal material
Explain the role of gut microbiota.
- Prevent colonisation by pathogens
- Excrete useful metabolites (e.g. short chain fatty acids)
- Ferment unused energy substrates
- Synthesise and excrete vitamins
- Produce hormones
- Play a role in circulation of bile acid between liver and small intestine
Through many of these, provide energy for good bacteria to proliferate.
What are different ways to maintain a healthy gut microbiota (e.g. if antibiotics caused the microbiota to be wiped out, resulting in possible proliferation of bad bacteria) ?
1) Probiotics: start replenish stock wiped out by antibiotics
2) Prebiotics: to stimulate growth of those good bacteria that weren’t wiped out
3) Bacteriotherapy: implant good bacteria from someone else through fecal transplantation
How do we initially get normal microbiota ?
Touching, kissing, breastfeeding help transfer microbiota from mother to child
Identify factors controlling gut microbiota.
- Physiological status
- Underlying disease (e.g. folate deficiency have depressed immune system, gastric acid deficiency also, level of antimicrobial peptide)
- Intestinal secretions
- Intestinal motility
- Immune mechanisms
- Environmental factors (climate, hygiene, diet)
- Use of antibiotics (can wipe out good bacteria)
How important is the GI tract in the immune system ?
GI tract is the primary immune organ in the body: contains 60% of total immunoglobulins and >10 million lymphocytes per gram tissue.
ALSO, GI microbiota has a strong influence on the development of the local and systemic immunity and in the regulation of immune functions.
How does pathogen recognition occur in the GI tract ?
PAMPS/MAMPS are pathogen/microbe associated molecular patterns, which are recognised by the host
These can be recognised by TLRs, NODs (nucleotide-binding oligomerisation domain-containing proteins), NLRs
Describe gut microbiota-gut mucosa interactions.
When TLR or NODs in the vili recognise a pathogen, they attach to the pathogen, and then start a pro-inflammatory cascade which activates NF-KB (transcription factor) which then activates cytokines and chemokines, which then produce more inflammatory molecules (interferons, TNF-alpha) in the lamina propria
Overall, the temporary state of inflammation helps to get rid of the pathogen
How are most of the GI infections acquired ?
- Via the oral-fecal route
- Some may occur due to commensals becoming pathogenic due to change in circumstance
What is an infection ?
When a micro-organism causes ill health.
Why is it difficult for pathogens to survive ?
Because they need to overcome host defenses and compete with the microbiota
How are intestinal infections generally acquired ?
- Ingestion of infected food and water
- Ingestion of bacterial toxins
- Use of oral antibiotics (disrupts homeostasis, can wipe out normal micobiota)
What are the main symptoms of gastroenteritis ? What part of the GI is affected ?
-Gastroenteritis mainly affects the small intestine
-Symptoms:
Nausea
Vomiting
Diarrhea
Abdominal discomfort
Define enterocolitis.
Inflammation involving the mucosa of both small and large intestine.
Define diarrhea, including symptoms. Which part of the GI is affected ?
- Abnormal fecal discharge characterised by frequent and/or fluid stool, involving increased fluid and electrolyte loss.
- Result of disease in small intestine.
Define dysentry, including symptoms. Which part of the GI is affected ?
- Inflammation disorder of the GI tract.
- Symptoms: often blood and pus in the feces. Also often accompanied by pain, abdominal cramps and fever
- Result of disease in large intestine usually
Define the Bristol classification.
“diagnostic medical tool designed to classify the form of human faeces into seven categories.”
Helps indicate notably diarrhea, constipation
What are the clinical effects of pathogenic invasion of GI tract ?
- Diarrhea/dysentry
- Malaena (tarry blood in stools, implying blood is coming from further inside, possibly stomach or small intestine)
- Blood in feces
- Pus in feces
- Abdominal cramps
- Fever
- Sepsis
What could frank blood in stools indicate ?
That bleeding likely occurring in large intestine
Identify examples of pathogens acquired from food, identifying the food they can be found in.
Escherichia coli (beef)
Salmonella spp. (chicken)
Bacillus cereus (re-heated rice)
Listeria spp. (cheese)
Identify examples of pathogens acquired from water.
Escherichia coli
Salmonella spp
Vibrio cholerae
Rotavirus
Identify examples of pathogens acquired from animals (esp. seafood).
Escherichia coli
Salmonella spp.
Clostridium perfingens
Yersinia enterocolitica
Identify common toxin-producing GI pathogens. What symptom are these associated with ?
Bacillus cereus C. botulinum C. perfringens E. coli (e.g. enterotoxigenic E. coli) Vibrio cholerae
Frequently associated with severe abdominal cramps.
