Microbiology of the Gut Flashcards
What makes up our gut flora?
Combination of all the bacteria interacting with each other that creates a healthy environment for them to grow
What are some structural host defences that protect us from all these organisms in our guts?
- seamless epithelium
- tight junctions
- sloughing/turnover
What are some mechanical host defences that protect us from all these organisms in our guts?
- peristalsis
- chewing
- fluid movement
What are some biochemical host defences that protect us from all these organisms in our guts?
- gastric acid
- bile
What are some immunological host defences that protect us from all these organisms in our guts?
- secretory IgA
- intra-epithelial lymphocytes
-What are some benefits of gut flora?
- colonisation resistance
- metabolites of benefit to the host
- normal development of immunity (tolerance, etc.)
- aids digestion
What is gastroenteritis?
Acute syndrome characterisation by gastrointestinal symptoms in any combination
What are the symptoms of gastroenteritis?
- nausea
- vomiting
- diarrhoea
- abdominal discomfort
What is diarrhoea?
- Frequent passage of loose, fluid, unformed stools.
→Increase in stool weight above 200g per day
What is diarrhoea characterised by?
- Increase in daily stool frequency and urgency
What is dysentery?
- Inflammatory disorder of the GI tract - usually in the large intestine.
What are the symptoms of dysentery?
Associated with blood and pus, pain, fever, abdominal cramps.
What is enterocolitis?
Inflammation involving the mucosa of the small and large intestine.
What is some damage resulting from infection of the gastrointestinal tract? PART 1
- pharmacological action of bacterial toxins
- local inflammation in response to a superficial microbial invasion
- deep invasion of blood and lymphatics
What is some damage resulting from infection of the gastrointestinal tract? PART 2
- dissemination of the organism to other body sites
- perforation/ulceration of mucosal epithelium
What are some mechanisms of bacteria/viruses/etc. that cause diarrhoea?
- bacterial toxins [eg. cholera]
- adherence [eg. E.coli]
- penetration and invasion
What types of flora are there?
Resident flora
Transient flora
Why do the color and texture of babies feces change a lot?
→change in organisms of the baby’s gut
What do the organisms from a baby’s gut change from and to?
→facultative anaerobes to obligate anaerobes
What does bifidobacteria produce and what does it prevent?
→produces lactic acid
→prevents the growth of gram-negative bacteria
Once a baby starts to wean what happens to the bifidobacteria?
→bifdobacter decreases and becomes bacteroides, clostridia and eubacteria
How many bacteria are there in the stomach?
Few bacteria due to the acidic conditions
Where do the bacteria increase?
→ The jejunum and duodenum
What are obligate anaerobes?
→bacteroides
→ bifidobacteria
→clostridia
What are facultative anaerobes?
E.Coli
What kind of bacteria is E.Coli?
Gram-negative
Going from the top to the bottom of the GI how do bacteria change?
→number and complexity of the species increases.
What two types of bacteria does a normal gut usually have?
→bacteroides
→firmicutes
What diseases are associated with microbiome alterations? PART 1
→Crohn’s disease
→Inflammatory bowel disease
→Clostridium difficile
What diseases are associated with microbiome alterations? PART 2
→Colon cancer
→Celiac disease
→Diabetes type I and II
→Mental health and depression
How do gut flora produce gut metabolites?
→Vitamin K, B12, organic acids
→Enhanced utilization of amino acids
How does gut flora aid digestion?
→Fermentation of sugars (10% of energy), H2 or methane, regulation of fat storage
What do probiotic organisms produce?
→lactic acid and organic acids
What do probiotic organisms do?
→get 10% absorbable energy from dietary fibre.
What is the function of microbial antagonism?
→Maintains flora through complex interactions
→Limits the growth of competitors and pathogens
How does gut flora prevent colonization?
→Bacteriocins (peptides that kill other bacteria)
→Reduced numbers of available epithelial receptors
→Keeps pH low
→Controls oxidative potential
What does loss of flora lead to?
→ Bacterial or pathogen overgrowth
What effects does ciprofloxacin have on flora and when does this return to normal?
→decrease in diversity with significant effects on 1/3rd of taxa
→ returns to normal in 4 weeks
What are clinical consequences of diarrhoea?
→Can lead to severe dehydration
→Excessive fluid and electrolyte loss
→Hypovolaemia, hypokalaemia
→Organ failure
What are the organisms that cause diarrhoea?
→Microorganisms
→Bacteria
→Viruses
What does chronic diarrhoea or malabsorption lead to?
→ steatorrhea
→ fat malabsorption
What does infective proctitis lead to?
→ ano-rectal STIs
What is associated with dyspepsia?
→ ulcers
→ H. Pylori
What is associated with dysphagia?
→oesophagus candida
What causes watery diarrhoea?
→ epithelial cells/enterocytes are damaged
→ absorption of fluid is stopped
→villi are damaged
→ crypt cells start hypersecreting
What do E.Coli toxins do?
→toxin migrates into the cell and causes changes to cAMP
→change protein kinases
→change chloride channels
How does changing chloride channels by E.Coli cause diarrhoea?
→There is hyperchloride secretion
→Causes osmotic flow of water following the chloride and fluid is secreted leading to diarrhoea.
How does EPEC E.COli work?
Binds to the brush border and the microvillus structure is destroyed so the enterocytes no longer works.
→ Adherence
How do viruses cause diarrhoea?
→Viruses can penetrate the enterocytes which destroy the cells.
→No absorption occurs and malabsorption happens with hypersecretion.
→There is villus atrophy and crypt hyperplasia develops, eventually the villi recover.
What is the microbiome affected by?
→diet
→ antibiotics
→surgery
→genes
