Gastrointestinal > Intro to Gut Microbiology > Flashcards

Intro to Gut Microbiology Flashcards

(66 cards)

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1
Q

What is the normal flora of the gut?

A

Flora normally present in all surfaces and mostly (99%) in the gut

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2
Q

What is meant by resident flora?

A

commensal organisms that are there for life

microbial melting pot

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3
Q

What is transient flora?

A

temporarily reduced, carried or changed due to environmental factors
- not permanent flora

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4
Q

Give an example where the flora changes in the body

A

organisms in baby’s gut change during weaning
e.g. baby to adult - weaning
Bifidobacterium (>90% of the flora) and utilises breast milk (gram +ve)
diet; environment; stress; hormones; age; transit time causes change from bifiobacterium →adult microbiota

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5
Q

Explain how baby faecal transition occurs

A
  1. Sterile meconium (first time baby
    defecates; green coloured)
  2. facultative anaerobes (baby acquires
    microbial flora)
  3. Strictly anaerobic gut (O₂ free environment
    in colon)
  4. Bifidobacterium
  5. After weaned off milk microbes change to
    adult-like gut microbiota (bacteroides)
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6
Q

Describe the biological features of bifidobacterium

A

Gram +ve Rod; branched

Produce lactic acid; prevent growth of G-ve bacteria that may try colonising baby’s gut

Metabolises breast milk → nutrients for baby and energy for itself

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7
Q

Describe the transition of bacteria when acquiring adult microbial flora

A

Weaning:
Bifidobacterium → bacteroides, clostridia & eubacteria (adult-like gut microbiota) anaerobic organisms living in lower half of colon

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8
Q

What is commensal flora?

A

one organism derives food or other benefits from another organism without hurting or helping it

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9
Q

Which part of the normal flora is commensal

A

No one species of gut flora is a commensal, but together the flora may be regarded as commensal (no harm to host)

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10
Q

What is the significance of the normal flora?

A

A combination of organisms produces normal flora allowing normal physiology of gut

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11
Q

Describe the distribution of bacteria in the gut

A

Bacteria distributed throughout GI Tract
Fewer in stomach due to high Acidity
More complex and larger mixture of bacteria as we progress through duodenum & ileum (esp. Terminal ileum)

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12
Q

Describe the flora in the colon

A

Colon: anaerobic environment, contains facultative and obligate anaerobes
Very large amount of complex mixtures of bacteria
E.g. bacteroides, clostridia, E.coli

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13
Q

How does disease affect the gut flora

A

Microbiome alterations (dysbiosis) are associated with disease states

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14
Q

How does Inflammatory Bowel Disease affect the distribution of bacteria?

A

In patients with inflammatory bowel disease, the distribution of bacteria is very different
Generalised diversity changes and species differ

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15
Q

What can cause gut flora dysbiosis?

A 
Crohn’s disease
Inflammatory bowel disease – ulcerative colitis
Irritable bowel syndrome – IBS
Clostridium difficile  
Colon Cancer
Allergy
Celiac disease (gluten)
Diabetes – type I and II
Obesity  (Bacteroidetes/Firmicute ratios)
Mental health and depression
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16
Q

How can we test faeces microbiota?

A

Take a DNA extraction, sequencing one of the genes encoded in bacterial genome that encodes for the 16s ribosomal RNA

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17
Q

What structural defences are present in the gut?

A

Seamless epithelium, tight junctions; High turnover

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18
Q

Describe the mechanical host defences of the gut

A

Peristalsis, chewing, fluid movement through gut, prevents pathogens adhering to gut

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19
Q

What biochemical defences are in the gut?

A

Gastric acid, bile, mucous are highly toxic to bacteria

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20
Q

What are the immunological defences of the gut?

A

Secretory IgA in lumen of mucosal surfaces binds to bacteria preventing epithelial binding, intraepithelial lymphocytes

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21
Q

What issues can be caused by microbes in the gut?

A

Spread of infections to the body

damage of barriers; pH change; overgrowth, AIDS

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22
Q

What are the benefits of the gut flora?

A
  • Colonisation Resistance
  • Metabolites produced of benefit to host
  • Normal development of immunity
  • Aids digestion
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23
Q

How is colonisation resistance beneficial to the gut?

A
  • blocks pathogens
  • gut full of commensals = hard for pathogens to get in,
    reproduce & cause disease
  • Hard because niche taken up by commensals
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24
Q

What beneficial metabolites are produced in

A

Vit K, B12, organic acids
Enhanced utilisation of amino acids
Butyrate for colonocytes – maintain anaerobiosis

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25
What is the effect of normal immunity development?
Increases tolerance; antigenic stimulation, Tregs, IL17
26
How does the gut flora aid digestion?
Fermentation of sugars (10% of energy released from colon); | Gas? H2 or methane; regulation of fat storage
27
What are probiotics?
organisms we think will contribute to a healthy biome
28
What are the functions of the probiotics?
Best probiotics produce lactic and organic acids ~10% absorbable energy from dietary fibre; ↑ diversity of polysaccharides for metabolism
29
Give examples of probiotics
Lactobacillus acidophilus, Bifidobacteria - B.longum, Bacteroides thetaiotaomicron Some Streptococci
30
What are the clinical uses of probiotics?
Control of diarrhoea in infants Relieve constipation Improve digestion of lactose
31
What are prebiotics?
nutrients that alter the gut ecosystem
32
What is the role of prebiotics?
Encourage good microbes to grow e.g. breast milk - ‘bifidus factor’ certain oligosaccharides e.g. fructooligosaccharides fermented in colon by probiotic organisms promotes growth of probiotes
33
What is a bacteriocin?
a protein produced by bacteria of one strain and active against those of a closely related strain
34
What is microbial antagonism?
When some organisms inhibit growth of other organism to limit growth of competitors and pathogens e.g. bacteriocins
35
What causes a loss of flora?
bacterial / pathogen overgrowth
36
What disrupts the normal flora the most?
Certain antibiotics (e.g. ciprofloxacin) disrupt our microbiome more than others
37
What is the consequence of loss of flora due to antibiotics?
Leads to antibiotic associated colitis as antibiotics reduce no. of gut flora and changed it => lead to overgrowth of clostridium difficile = pseudomembranous colitis
38
What is colitis?
inflammation of colon caused by introduction of antibiotics
39
Outline the effects of microbial antagonism
- Limits growth of competitors + pathogens - Bacteriocins - Reduced no. of available epithelial receptors - Keeps pH low - Controls oxidative potential (anaerobic growth) - Limits pathogen growth - Occupy all niches - High numbers - Waste products
40
What is gastroenteritis?
Acute syndrome characterised by generalised GI symptoms in any combination including: - Nausea - Vomiting - Diarrhoea - Abdominal discomfort
41
What is diarrhoea?
Watery / liquid stools, usually with an increase in stool weight above 200 g per day and an increase in daily stool frequency and often a sense of urgency
42
What are the clinical consequences of diarrhoea?
- severe dehydration, excessive fluid and electrolyte loss, hypovolaemia; hypokalaemia; organ failure - long-term morbidity and reduced growth
43
What is dysentery?
Inflammatory disorder of GI Tract, usually large intestine; often associated with blood & pus (as penetrated natural barrier). As well as pain, fever and abdominal cramps
44
What is enterocolitis?
Inflammation involving mucosa of small and large intestine e.g. Crohn’s Disease
45
What is the impact of diarrhoeal diseases?
Many deaths a year (2 million) | Especially under 5’s (undergo multiple episodes a year) -> massive global health burdens (it is preventable)
46
What are the main causes of diarrhoeal diseases?
Infectious mciroorganisms e.g. - Bacteria - Viruses - Parasites - protozoal and worms
47
How are diarrhoeal diseases spread?
infectious micro organisms shed in faeces and spread to new host (faecal-oral route)
48
What are the characteristic patterns of gut infections?
Acute watery diarrhoea Dysentery = Acute / chronic diarrhoea + blood + pus Poor Fat absorption = chronic diarrhoea / malabsorption Infective proctitis : ano-rectal STIs
49
Which pathogen is responsible for travellers diarrhoea?
normally e. Coli
50
Explain how food poisoning occurs
Diarrhoea from eating food containing toxins or bacteria in food that grow inside us and produce toxins
51
Which patients are classed as immunocompromised hosts?
- AIDS patietnts - immunosuppressed - elderly or very young
52
What causes antibiotic related diarrhoea?
altered normal flora
53
What damage is caused by an infection of the GI tract?
Pharmacological - action of bacterial toxins local or distant to site of infection e.g. cholera Local inflammation - in response to superficial microbial invasion e. g. Shigella dysentery or Campylobacter food-poisoning Deep invasion - to blood and lymphatics and dissemination of the organism to other body sites – enteric fevers e.g. Typhoid fever or Hepatitis A Perforation/ulceration - of mucosal epithelium peritonitis; intra-abdominal abscess (e.g. Entamoeba)
54
What are the different mechanisms of diarrhoea?
Bacterial Toxins Adherence Penetration + invasion
55
Describe how bacterial toxins cause diarrhoea?
- Enterotoxins are toxins that affect the gut - Exotoxins effect fluid/electrolyte transport by increasing / decreasing cAMP - Cytotoxins direct cell damage
56
How does pathogen adherence cause diarrhoea?
e.g. E. coli EPEC enteropathogenic adhere to cells below and damage epithelium
57
Explain how invasion and penetration by pathogens can lead to diarrhoeal disease
Disruption of tissue architecture and function - enteroinvasive Inflammation
58
What is the function of villus in the gut?
Main function is absorption
59
What is the role of crypts in the gut?
Mainly secretion
60
What are heat stable toxins?
Toxins that are not destroyed even when heated. If consumed, effects will prevail
61
What are heat liable toxins?
Heat-liable toxins are inactivated through cooking
62
Outline the mechanism of action of toxins in the villi causing diarrhoeal diseases
Affect electrolyte channels in the enterocytes by: Heat labile toxin stimulate AC, causing cAMP to disregulate protein kinase → changes Cl- channel causing electrolyte imbalance and thus fluid balance Similar with GC
63
Explain how mucosal injury can lead to diarrhoea
Virus / bacteria can penetrate into villi resulting in villous atrophy. There’s no absorptive capacity = anti-absorptive diarrhoea (malabsorption)
64
Why does damage to gut mucosal surface cause diarrhoea?
=> immediately get crypt hyperplasia to try replace villus; crypt tries to regenerate villus. At this time you get lots of secretion, so combination of atrophy and then high secretion = anti-absorptive diarrhoea, eventually recovering (takes up to 3 days)
65
What viruses cause gut disorders?
- Astrovirus (star) - Calicivirus (Star of David) - Rotavirus (wheel) - Poliovirus (featureless) - Norwalk SRSVs) Norovirus (ill defined lace-like appearance)
66
Which properties of intestnal physiology are affected by the microbiome?
- Energy balance regulation + pathophysiology of obesity - Modulates digestion + absorption - ↑ energy harvesting - Microbiome influenced by diet, antibiotics, surgery + genes - Microbiome contributes to host metabolism + energy homeostasis beyond nutritional processing e.g. endocrine function and inflammatory signals

Gastrointestinal (18 decks)

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