Gut Normal Flora

Question 1

Tissue tropism

definition

Answer 1

Bacterial preference for certain tissues for growth.

• because the host ptovides essential nutrients and growth factros for the bacterium
• suitable O₂, pH and temperature for growth of the organism

Question 2

Specific adherence

tissue tropism

Answer 2

Bacteria colonize specific tissue or site because of their ability to adhere to that particular tissue

• this involves complementary interactions between 2 surfaces
• specific adherence: involves biochemical interactions between bacterial ligands or adhesins and host cell molecular receptors
  
  • ​Bacteria: capsules, fimbrea and cell walls
  • Host cell receptor: Glycoprotein molecules

Question 3

When does biofilm production occur

Answer 3

When one bacteria attaches to surface and then secretyes an exopolymer of carbohydrate slime

Question 4

Functions of biofilm

Answer 4

• Imbeds the bacteria
• attracts other microbes for protection and nutritional advantage

Question 5

Biofilm examples

Answer 5

• dental plaque
  
  • involves indogenous bacteria
• some indogenous bacteria make their own biofilm others colonize the biofilm or colonize that of other species

Question 6

Gut flora overview

Answer 6

• largest reservoir of normal flora
• 60% of dry mass of feces
• around 500 diffferent species
  
  • 99% are from 30 or 40 species
• fungi
• protozoa
• influenced by age, diet, culture, antibiotic use

Question 7

Variation of gut flora

Answer 7

longitudinal and horizontal (lumen vs epithelium)

• Esophagus only a few bacteria which are swallowed with saliva and food
• Stomach has few bacteria because of the high acidity of gastric juices
• Proximal SI sparse gram positive flora
  
  • ​Lactobacilli
  • Enterococcus faecalis
• Distal SI more bacteria
  
  • E coli
  • Bacteroides
  • Lactobacilli
  • Enterococci

Question 8

Gut flora of large intestine

Answer 8

• qualitatively similar to feces
• Coliforms are more prominent
• Enterococci
• Clostridia
• Lactobacilli
• prominent species
  
  • ​​Bacterioides
  • Anaerobic lactic acid bacteria
    
    • Bifidobacterium bifidum
    • significantly outnumber E coli
• sometimes anaerboic methanogens

Question 9

Function of normal GIT flora

Answer 9

• produce vitamins
• nutrition
• aid digestion
• protect host from infection by exogenous microorganisms
• stimulate the activity of the immune system
• BACTEROIDES
  
  • ​produces carcinogenic metabolites
  • increased incidence of colon cancer

Question 10

NF and vitamin synthesis

Answer 10

• excess to needs of bacteria and are therefore absorbed by host
• Enteric bacteria secrete VIT K and VIT B12
• Lactic acid bacteria produce B vitamins

Question 11

Most important effect of NF

Answer 11

prevent colonization by pathogenic bacteria

Question 12

NF and antagonizing other bacteria

Answer 12

• Non specific fatty acids and peroxoidases
• HIghly specific bacteriocins

Question 13

Nf stimulate which type of immunity

Answer 13

antibody mediated

1. against normal flora
   
   • natural AB
2. Cross react with related non indigenous

Question 14

Harmful effects of NF

Answer 14

1. Bacterial synergsim
   
   • Supplies vitamin or growth factor needed by a pathogen
2. Competition for nutrients
   
   • usually bacteria absrorb nutrients and transform them into metabolites for the host
   • sometimes nutrients are lost to the host
3. Induce low grade toxemia
   
   • Endotoxin in circulation
   • if small amounts–natural AB
4. Agents of disease
   
   • if they reacha site where they can not be tlerated or restricted by the immune system
   • many NF are potential pathogens if they gain access to compormised tissue where they invade causing disease
5. Transfer to succeptible host
   
   • URT
     
     • N meningitidis
     • S pneumo
     • H influ
     • Staph aureus
     • Potential pathogens
       
       • E coli
       • Salmonella
       • Clostridium

Question 15

NF and colon cancer

Answer 15

• through production of carcinogens co/procarcinogens
• Some bacteria strongly increase damage to DNA initiated by heterocyclic aromatic amines formed in cooked meat
• Some intestinal bacteria uptake these compounds and detox them
• Bacteroides (vulgatus, stercoris) and Clostridium
  
  • increase incidence and growth rate of colonic tumors
• Lactobacillus (acidophilus, (Eubacterium) aerofaciens ) and bifidobacteria
  
  • prevent tumorigenisis

Question 16

Nf and IBD

Answer 16

• CROHNS
  
  • intestinal T cells are hyperactive against bacterial antigens
• Crohns and UC
  
  • Increased IgG against broad spectrum of commensal bacteria
    
    • activate complement unlike igA causing damage
  • More bacteria attached to epithelial surface
    
    • Bacteroides intracellularly

Question 17

Probiotics

Answer 17

• maintain balance
• reduce growth of normal bacteria
• Lactobacillus
  
  • acidophilus
• Bifidobacterium
  
  • bifidus
• yeasts
  
  • saccharomyces boulardii
• yogurt
• fermented and unfermented milk
• miso
• temphe
• juices
• soy beverages

Question 18

benefits of probiotics

Answer 18

• Digests certain sugars and proteins.
• Facilitates absorption of certain minerals, such as calcium, magnesium, and iron.
• Regulates appropriate storage of fat in the body.
• Prevents bloating, gas, and yeast overgrowth
• .Manufactures vitamin K and B vitamins sometimes otherwise in short supply.
• Deprives invaders of nutrients, secretes acids that less friendly microbes can’t tolerate.
• Strengthens the lining of the gut to help block dangerous pathogens, toxins, and allergens.
• Stimulates immune system by increasing T cells, producing natural
• antibiotics/antifungals.
• Metabolizes and recycles hormones, including estrogen, thyroid hormones, and phytoestrogens.
• Helps detoxify drugs and other harmful compounds.
• Exerts anti tumor/anti cancer effects

Question 19

prebiotics

Answer 19

• non digestible food ingredients
• selectively stimulate growth/activity of beneficial microirganisms already prsent
• synergistic with probiotics