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BDS2; FHHD > M7: Bacteria affecting GIT > Flashcards

M7: Bacteria affecting GIT Flashcards

1. Give a simple account of the composition of normal gut flora 2. List the main types of GIT infections, including food poisoning, diarrhoea, enteric fever and cholera 3. Summarise the modes of transmission of such infections and the principle methods avaliable for their control 4. Outline the main features and pathogenic mechanisms of common GIT bacteria including Escherichia, Salmonella, Shigella, Vibrio, Campylobacter, Klebsiella, Proteus, Pseudomonas

1
Q

List ways in which the GIT limits exposure of the host immune system to the microbiota

A
  1. Via epithelial and mucus layer
  2. Biochemically via enzymes and antimicrobial proteins
  3. Immunologically via IgA and epithelia-associated immune cells
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2
Q

What is the normal gut flora function

A

To maintain gut homeostasis by

  • strengthening the gut integrity
  • shaping the intestinal epithelium
  • harvesting energy
  • protecting against pathogens
  • regulating host immunity
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3
Q

Bacteria affecting stomach and the stomach environment

A

Low pH, bile, inhibitory usually sterile environment

H. pylori can resist - causes gastritis

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4
Q

Small intestine commensal flora

A

Jejunun - Enterococci, lactobacilli

Ileum - Enterobacteriaceae, Bacteroides fragilis (gram -ve anaerobes)

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5
Q

Large intestine commensal flora

A

Strict anaerobes (obligate)

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6
Q

Why is the normal GI flora beneficial

A

Because it provides competition against potentially pathogenic species

Attenuates mucosal immune response to pathogen so it controls inflammation

It enhances integrity of the epithelial barrier by provided nutrients for colonic epithelium

Maintains the gut mucosa and metabolism of toxic compounds

Produces folate and vitamin K from dietary precursors

Produces luminal IgA

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7
Q

What causes diarrhoeal disease

A

It is a major cause of illness in developing countries and occurs due to socio-economic factors such as

  • lack of clean water
  • sewage disposal
  • food quility/balance
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8
Q

What are the two main mechanisms of diarrhoeal disease

A
  1. Invasive = bacterial invasion of tissues

2. Exotoxin = secretion in food of live bacteria

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9
Q

Bacteria involed in invasive diarrhoeal disease and what are the symptoms

A

Salmonella enteritis
Shigella dysenteriae - bacillary dysentery

Cramps in abdomen, pus and blood in stools

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10
Q

What is escherichia

A

Gram -ve rod, lactose fermenter

E. coli is the most common species

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11
Q

How does escherichia adhere to host cells

A

Via fimbriae on the cell surface and pili

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12
Q

What can E. coli cause

A
  • GI infections
  • UTIs
  • Septic infections (wounds, abscesses)
  • Neonatal meningitis
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13
Q

What protects E. coli from the host immune response

A 
O = somatic antigens
K = capsular antigens

Protect from complement activation and phagocytosis

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14
Q

What are the features of ENTEROPATHOGENIC E. coli

A
  • Attachment and effacing lesions of intestine
  • Acute enteritis of infants
  • Tropical countries
  • High mortality
  • Non-invasive
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15
Q

What are the features of ENTEROTOXIGENIC E. coli

A
  • Adhere to epithelium of small intestive
  • Toxin mediated causing fluid loss
  • Brief illness: vomiting, abdominal crapms, loose stools
  • Acute enteritis = traverlers diarrhoea
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16
Q

What are the fetures of ENTERO-INVASICE E. coli

A
  • Causes dysentery-like disease

- Invasive with bacteria entering epithelial cells of large intestine and multiplying here

17
Q

What are the features of VERO CYTOTOXIGENIC E. coli

A
  • Infection can lead to renal failure in severe cases
  • Toxins produce VT1/VT2
  • Severe outbreaks in paediatric and geriatric populations
  • Haemorrhagic colitis (bloody diarrhoea)
18
Q

Outline virulence mechanisms of E. coli

A

EPEC = adherence to epithelium via cytoskeletal rearrangement (calcium and electrolyte loss)

ETEC = toxin causing adenylate cyclase ribosylation and cAMP accumilation - leads to fluid secreteion

EIEC = epithelial cell invasion, destruction and spread

VTEC = Vero-toxin: inhibits ribosomal RNA and so stops protein synthesis

19
Q

What is salmonella

A

Gram -ve bacilli, inhabit animal intestines, non-lactose fermeters

O (somatic) and H (flagellar) antiges

20
Q

Outline pathogenesis of salmonella

A

Bacteria attach to epithelium of ileal mucosa

Invade and multiply in tissues

21
Q

Salmonella gatro-enteritis symptoms

A

Cramps, diarrhoea, fever, vomiting, severe dehydration, renal failure

22
Q

Where is the salmonella bacteria found

A

Poorly butchered meats
Eggs
Animals and human carriers

23
Q

What is shigella

A 
Gram -ve rods, non lactose fermeting 
- S. dysenteriae 
- S. flexneri
- S. boydi 
These cause bacillary dysentery and frequent passage of bloody mucopurulent stools
24
Q

How is shigella spread

A

Faecal-orally

Due to poor hygine

25
Q

What is klebsiella

A

Gram -ve, lactose fermenter, capsule and mucoid colonies present

There is an emergence of antibiotic resistance

26
Q

What can klebsiella cause

A

UTIs
Severe bronchopneumonia
Lung abscesses
Serious cause of hospital infection via surgical wounds

27
Q

What is proteus

A

Gram -ve, non lactose fermenter, motile

28
Q

What does proteus cause

A

UTIs in children
Wound infections
Infection in surgery

29
Q

How can GI bacteria from faeces be selectivelt isolated

A

MacConkey’s agar containing

  • bile salts (selective agent)
  • lactose (carbon source)
  • pH indicator

OR

Alternative selective medium = CLED

30
Q

What are vibrio species

A

Gram -ve rods, curved comma shaped, motile-polar flagellum

31
Q

What does vibro cholerae cause

A

Cholera

  • vomiting
  • cramps
  • rive water stools (perfuse watery diarrhoea)
  • electrolyte outflow into bowel
  • rapid dehydration
  • death in 12-24 hours
32
Q

How is V. cholerae spread

A

Contaminated water and foods

Common in overcrowding and poor hygiene areas

33
Q

What does V. parahaemolyticus cause

A

Explosive diarrhoea
Japan and Singapore (raw seafood)
Symptoms = after 3 days

34
Q

What is pseudomonas aeruginosa

A

Opportunistic pathogen

  • important in nosocomial infections
  • exogenous infections: wounds, eyes, burns
  • endogenous infections: immunocompromised patients
35
Q

What is campylobacter

A

Gram -ve, spherical rods

Common cause of infective diarrhoea in developed countries

Source = animals and birds

36
Q

Symptoms of campylobacter infection

A

C. jejuni
C. coli

Abdominal pain
Diarrhoea
Fever
Nausea

37
Q

What is helicobacter pylori

A

Gram -ve rod, colonises stomach in gastric mucosa causing gastritis, important in peptic ulceration and produces high amounts of urease

BDS2; FHHD (26 decks)

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