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Clinical food and microbiology > 9. GITI > Flashcards

9. GITI Flashcards

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1
Q

How is a gastrointestinal infection a food-associated (borne) infection?

A
  • ‘food’ acts as a vehicle for transmission
  • food-handlers contaminate ‘food’
  • then pathogen is consumed
  • Eg.. Salmonella, Campylobacter
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2
Q

How does GI infection cause food poisoning?

A
  • toxin present in food; gets consumed
  • Eg.. Staphylococcus aureus
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3
Q

How does GI infection cause Antibiotic-associated diarrhoea?

A
  • BS antibiotics disrupt normla gut flora
  • over-growth of pathogenic microorganism
  • Eg.. Clostridum difficile
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4
Q

What is Clostridium difficile?

A
  • bacillus difficilis; normal component of faecal flora of 70% newborn babies and 2-3% healthy adults
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5
Q

What are the characteristics of Clostridium difficile?

A
  • gram-positive rod
  • strictly anaerobic
  • spore forming microorganism
  • toxin producing
  • has >100 different genetic types
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6
Q

What are the risk factors for C.diff infection?

A
  • spores; persistent, transmissible, resistant to antimicrobials
  • hospitalisation; length of stay & age (65)
  • broad spectrum antibiotic use
  • hygiene/dirty environment
  • close proximity of patients
  • naso-gastric tubes
  • contaminated equipment
  • BP monitoring cuffs
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7
Q

What is the summary of the C.diff infection pathway?

A
  • susceptible patient ingests spores; resist stomach acid
  • favourable conditions for spore germination; pH6-6.8, bile salts, aa (aspartic acid, histidine)
  • vegetative cells; flagellated; metabolically active; produce potent toxins
  • vegetative cells produce spores in the colon; excreted in diarrhoea
  • spores can survive in clinical setting
  • infection cycle continues
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8
Q

How do C.diff spores germinate?

A
  • germination initiation; germinants include, sugar, aa, nutrients
  • loss of heat resistance and ions (K, H, Na) and Ca-DPA complex
  • partial rehydration of core
  • hydrolysis of cortex and degradation of SASPs
  • Rehydration of core and restoration of metabolic activity
  • sensitive to antimicrobials
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9
Q

What is a spore resistant to?

A

antimicrobials

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10
Q

What is a germinating cell sensitive to?

A

antimicrobials

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11
Q

How does C.diff adhere and multiply?

A
  • uses S-layer proteins (adhesins)
  • flagella
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12
Q

How does C.diff produce toxins?

A
  • genes located on PaLoc
  • Toxin A: enterotoxin
  • Toxin B: cytotoxin
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13
Q

What are the function of toxins produced by C.diff?

A
  • modification of Rho proteins
  • Stimulate cytokine production
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14
Q

What is the MOA for C.diff toxins A and B?

A
  1. Toxins A and B enter gut lumen and attach to surface of intestinal epithelial cells.
  2. toxins cause opening of tight junctions between cells, compromising integrity of barrier.
  3. The toxins target Rho proteins, which maintain the cytoskeleton. Toxins inactivate Rho proteins leading to disruption.
  4. Actin cytoskeleton is disrupted causing ‘cell rounding’.
  5. Damage stimulates production of IL-8, attracting immune cells; immune response activation
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15
Q

What are the clinical manifestation of C.diff?

A
  • asymptomatic
  • explosive diarrhoea
  • pseudomembranous colitis
  • fulminant colitis
  • death
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16
Q

What did the C.diff ribotype 027 cause in 2003?

A

2003: Canadian outbreak
7000 sufferers, 600 deaths
- higher levels of toxin A + B
- base pair depletion in toxin regulating gene
- resistant to ciprofloxacin/ moxifloxacin

17
Q

What did the C.diff ribotype 027 cause in the UK 2004?

A
  • Stoke Mandeville
    12 deaths, 300 infections
  • Royal Devon and Exeter
    13 deaths
  • Maidstone and Tunbridge Wells
    90 deaths, 1170 infections
18
Q

What is the PaLoc?

A
  • positive regulator gene controlling expression
  • encodes for protein porin associated with release of Toxin A/B from the cell
  • downstream negative regulatory gene controlling expression of tcdA and tcdB
19
Q

How can C.diff infection be spread?

A
  • close patient contact
  • filthy conditions:
    shower cubicles
    eating/drinking area
    faecal stained patient commodes
20
Q

What is the lab diagnosis of C.diff associated diarrhoea?

A
  • clinical sample; faeces
  • cat2 pathogen
  • non-culture techniques; toxin detection (cell lines/ EIA) and GDH detection (EIA)
  • culture; selective agar (CCFA)
  • typing; ribotyping; outbreaks
21
Q

How can a culture be used for lab diagnosis?

A
  • selective CCFA
    (cefoxitin, cycloserine, fructose)

identification of colonies
- ground-glass appearance
- odour of colonies

22
Q

Why is Ribotyping used?

A
  • genomic DNA encoding for 16S and 23S rRNA is a highly conserved region
  • genetic info coding for tRNA will vary less within bacteria of same strain than diff strain
  • it is highly discriminatory
23
Q

What is the basic principle of Ribotyping?

A
  • C.diff genomic DNA is digested with appropriate restriction endonucleases and separated by gel electrophoresis
  • specific universal oligonucleotide probes target conserved regions
  • it is visualised
  • band pattern compared to a database of established C.diff ribotypes
24
Q

What are antimicrobial treatment strategies for C.diff?

A
  1. discontinuation of precipitating antibiotic
  2. replacement fluid and electrolytes
  3. antibiotics for treating C.diff

oral vancomycin (250mg QDS; 10-14 days)
oral metronidazole (250mg QDS; 10-14 days)

25
Q

What are biotherapy treatment strategies for C.diff?

A

aim: to restore the gut microbiome
- probiotics
- faecal transplantation

26
Q

How can C.diff be prevented?
(1)

A
  • narrow spectrum antibiotics
27
Q

How can C.diff be prevented?
(2)

A

Prompt implementation of enteric precautions
-isolation of patient; cohort wards
- effective hand hygiene
- disposable equipment

28
Q

How can C.diff be prevented?
(3)

A

Elimination of spores from the environment
- spores resistant to common disinfectants
- hypochlorite/ superoxides
- soap/ detergent and scrubbing

Clinical food and microbiology (12 decks)

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