Introduction to microbiology of the gut Flashcards
What types of flora are there?
→Resident flora - for life,commensal organisms
→Transient flora - temporarily reduced - carried or changes
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 babys gut change from and to?
→facultative anaerobes to obligate anaerobes
What does bifidobacter 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 bifidobacter?
→bifdobacter decreases and becomes
→bacteroides, clostridia and eubacteria
How many bacteria are there in the stomach?
→There are few bacteria due to the acidic conditions
When do the bacteria increase?
→ As you go into the jejunum and duodenum
→ Mainly lactobacillus
What are obligate anaerobes?
→bacteroides
→ bifidobacter
→clostridia
What are facultative anaerobes?
→E.Coli
What kind of bacteria is E.Coli?
→gram negative
How many bacteria per gram are there in feces?
→10x11 bacteria per gram
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?
→Crohn’s disease →Inflammatory bowel disease →Clostridium difficile →Colon cancer →Allergy →Celiac disease →Diabetes type I and II →Obesity (bacteroidetes/firmicute ratios) →Mental health and depression
How do scientists find bacteria in the gut?
→targeting and sequencing 16S rRNA is how scientists find the bacteria in the gut.
What are the host defences against pathogens?
→Structural
Seamless epithelium, tight junctions, sloughing/turnover
→Mechanical
Peristalsis, chewing, fluid movement
→Biochemical
Gastric acid, bile, mucus
→Immunological
Secretory IgA, intraepithelial lymphocytes
What are the 4 benefits of gut flora?
→Colonization resistance - blocks pathogens
→Metabolites of benefit to host
→Normal development of immunity
→Aids digestion
How do gut flora produce gut metabolites?
→Vitamin K, B12, organic acids
→Enhanced utilization of amino acids
→Butyrate for colonocytes - maintain anerobiasis
How do 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 - competition between flora
→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 →Limits pathogen growth →Occupy all niches →High numbers Waste products
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 is diarrhoea defined as?
→Defined as watery or liquid stools
→Increase in stool weight above 200g per day
What are clinical consequences of diarrhoea?
→Can lead to severe dehydration →Excessive fluid and electrolyte loss →Hypovolaemia, hypokalaemia →Organ failure →Long term morbidity and reduced growth
What is the global impact of diarrhoea?
→3 billion episodes per year
→1.3 million deaths per year due to dehydration
What are the organisms that cause diarrhoea?
→Microorganisms →Bacteria →Viruses →Parasites - protozoal and worms →Shed in feces and transmission to new hosts
What is dysentery and what is it associated with?
→Inflammatory disorder of GI tract - usually large intestine
→Often associated with blood and pus
What are the symptoms of dysentery?
→Pain
→ fever
→abdominal cramps
Acute of chronic diarrhoea + blood + pus = ?
= dysentery
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 are the 4 types of damage caused by GI infection?
→Pharmacological action of bacterial toxins
→Local inflammation in response to superficial microbial invasion
→Deep invasion to blood and lymphatics and dissemination of the organism to other body sites
→Perforation/ ulceration of mucosal epithelium
Peritonitis, intra abdominal abscess
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 the osmotic flow of water following the chloride and fluid is secreted leading to diarrhoea.
How does EPEC E.COli work?
→Enteropathogenic E.Coli 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 as a result of this you get crypt hyperplasia, eventually the villi recover.
What are the 3 mechanisms of diarrhoea and what organisms cause this?
→ Bacterial toxins - E.coli
→ Adherence - E.coli
→ Penetration and iNvasion - Viruses
What is the microbiome affected by?
→diet
→ antibiotics
→surgery
→genes
