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DEN303 - IHD > Pathogens of the Gastro-intestinal tract > Flashcards

Pathogens of the Gastro-intestinal tract Flashcards

1
Q

Gastroenteritis

A

Syndrome characterised by GI-symptoms including nausea, vomiting, diarrhoea and abdominal pain

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2
Q

Diarrhoea

A

Abnormal faecal discharge characterised by frequent and/or fluid stool. Associated with increased fluid and electrolyte loss- often disease of small intestine

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3
Q

Dysentery

A

Abnormal inflammation of GI-tract: often blood and pus in faeces and pain, fever, abdominal cramps- often disease of large intestine

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4
Q

Enterocolitis

A

Inflammation of mucosa of small and large intestine

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5
Q

Defences

A 
Mouth 
Oesophagus 
Stomach 
Small intestine 
Large intestine
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6
Q

Defences - MOUTH

A

Flow of liquids
Saliva
Lysozyme
Normal bacterial flora

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7
Q

Defences - oesophagus

A

Flow of liquids

Peristalsis

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8
Q

Defences - stomach

A

Acid pH

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9
Q

Defences - small intestine

A 
Flow of gut contents
Peristalsis 
Mucus - bile 
Secretory IgA
Lymphoid tissue (payer's patcheS) shedding and replacement of epithelium 
normal flora
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10
Q

Defences - LI

A

Normal flora
peristalsis
shedding and replication of epithelium
mucus

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11
Q

Food poisoning

A

Ingestion of toxins or poisons in food e.g bacterial or heavy metal
Bacteria grow and multiply in food
Cooking kills bacteria but toxin still active - intoxication

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12
Q

Food poisoning toxin sources

A

Staph aureus
Growth in food after human contamination
Products, cooked meats, prepacked sandwiches
50% of strains produce heat stable enterotoxins
Resistance to stomach acid and digestive enzymes - nasopharyngeal carriage
3-6hrs of severe vomiting - complete recovery

Botulism - clostridium botulinum
Heat stable toxin ingest din food, leads to flaccid paralysis and death covered in anaerobe lecture
infant most common

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13
Q

Bacillus cereus

A

Self limiting

Gram positive, spore former

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14
Q

The stomach

A

Gastric acid pH 1-2
Effective barrier to most infections
Many bacteria pass through before infecting lower GI

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15
Q

Helicobacter pylori - gastric ulcers

Infective cycle

Treatment

A

Produces urease
Protective cloud during transit to gastric mucin layer
Ammonia basis of breath test

Infection
Inflammation of gastric mucosa often asymptomatic
Produces ulcer - gastric inflammation may lead to duodenal or gastric ulcer
Severe complications can include perforated ulcer

Treatment now with proton-pump inhibitor PLUS metronidazole/ amoxicillin and Clarithromycin

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16
Q

Food associated infections

A

Mainly spread faeco-orally

Ingestion of contaminated food containing infectious dose of bacteria

17
Q

Diarrhoeal treatment

A

Fluid and electrolyte replacement is essential
Antibiotic treatment often not successful and may worsen problem as it wipes out competing organisms or stimulates toxin production

18
Q

Diarrhoeal disease - e. coli

A

Gram-negative motile rod
Major cause of diarrhoeal disease and gastroenteritis worldwide
Complications include HUS
Many genetically distinct disease causing strains
Some strains reside in normal commensal flora
Others infect urinary tract and cause meningitis
Diarrhoea: Ingested in food or via fecal-oral transmission route.
Genetic diversity dependent on plasmid, lysogenic phage and transposon encoded ‘pathogenicity islands’

19
Q

Lab detection of E coli

A

Lactose fermentation

20
Q

E.coli strains - EPEC

Features
Mechanism

A

Enteropathogenic
Bundle forming pili to attach
Type III secretion system injects proteins into host to manipulate cytoskeleton

Tir- translocated intimin receptor
Intimin - mediates intimate attachment to epithelial cells

Attaching and effacing lesion
Leads to watery diarrhoea

21
Q

ETEC

A

Enterotoxigenic E.coli - toxin producing
Attach via adhesive pili
Produce Heat stable ST and Labile enterotoxins that cause diarrhoea
Common cause of Delhi Belly

22
Q

EIEC - enteroinvasive

A

Invade and destroy epithelial cells

Bloody diarrhoea

23
Q

EHEC

A

Attachment similar to EPEC- pedestals
Produce Vero-toxin (Also called Shigella-like toxin)- STx
STx (verotoxin) is a potent diarrhoeal toxin (and has receptor on kidney cells) acts via damaging cells directly
EHEC infections also cause hemorrhagic colitis- Bloody diarrhoea- destruction of mucosa>bleeding> spread to kidneys

HUS- Haemolytic Urinary Syndrome

	- This may lead to kidney failure (15% cases)
	- O157:H7 strain most well known
24
Q

2011 outbreak: O104:H4

A
  • EHEC/EAEC strain: shiga-toxin, multi drug resistant, aggregative pili- Nasty!
    Spring/summer 2011
  • Outbreak focussed in Germany: 3,000 cases (857 HUS); 50 deaths
  • Possible source- Fenugreek seeds from Egypt; raw beansprouts implicated also, WHO advises NOT eating raw.
25
Q

Shigella

A

Shiga toxin producing (similar to EHEC)
Shigella dysenteriae
– bacillary dysentry, Bloody stools
Shigella sonnei and flexneri
milder forms
Low infectious dose 10-100 cells – sometimes ID50
Non-lactose fermenters (Maconkey agar, Hektoen enteric- green no H2S)
Common in poorer countries
Spread fecal-orally, often via water contamination

26
Q

Salmonella

A

Most common food associated pathogen in UK
Spread from food - mainly chicken and dairy
Invade M cells then spread to surrounding epithelium
Usually a severe but self limiting diarrhoea and enterocolitis

Salmonella enterica subsp. Cause uncomplicated diarrhoea
typhimurium
enteritidis

27
Q

S. typhi - typhoid (enteric) fever

A 
Cause of typhoid 
Infection initiates in the intestine 
Spreads systematically as is transported in macrophages around body 
Causes increasing fever over 2 weeks 
Complications -
28
Q

Campylobacter spp.

A

Number one cause of food poisoning
Jejuni variety most common
Acquired by ingestion of contaminated food
Major reservoir in chickens
Symptoms like shigellosis and salmonellosis
Ulceration

29
Q

Cholera

mechanism

A

Most common historical cause of GI disease
Caused by motile gram -ve comma shaped
8 worldwide pandemics

vibrio cholerae ingested
sensitive to stomach acid
colonisation of SI depends on motility, production of mucinase, attachment to specific receptors
toxin production
loss of fluid as toxin causes release of chloride ions into small intestine and water follows
massive diarrhoea
1-2 litres of fluid/hr
Rapid fluid and electrolytes replacement
rice water stool

30
Q

Prevention

A

Vaccines have been unsuccessful but several available with only temporary immunity gained-
WHO trialling 2 vaccines currently with protection 6m to 2y.

Best prevention method is improvement of water system and sanitation- but hard to get aid for that… especially in war-torn/ lawless regions

31
Q

Viral causes of GI-infections

A

Of the 3 million infants that die from gastroenteritis 20% are viral sources
Major problem in developing countries
Children may have 60 days of diarrhoea per year – major effect on growth and nutrition
Mainly oral-fecal
Very hard to identify non-bacterial cases
Not until 1972 were viruses isolated from faeces

DEN303 - IHD (58 decks)

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