Pathogens of the Gastro-intestinal tract

Question 1

Gastroenteritis

Answer 1

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

Question 2

Diarrhoea

Answer 2

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

Question 3

Dysentery

Answer 3

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

Question 4

Enterocolitis

Answer 4

Inflammation of mucosa of small and large intestine

Question 5

Defences

Answer 5

Mouth 
Oesophagus 
Stomach 
Small intestine 
Large intestine

Question 6

Defences - MOUTH

Answer 6

Flow of liquids
Saliva
Lysozyme
Normal bacterial flora

Question 7

Defences - oesophagus

Answer 7

Flow of liquids

Peristalsis

Question 8

Defences - stomach

Answer 8

Acid pH

Question 9

Defences - small intestine

Answer 9

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

Question 10

Defences - LI

Answer 10

Normal flora
peristalsis
shedding and replication of epithelium
mucus

Question 11

Food poisoning

Answer 11

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

Question 12

Food poisoning toxin sources

Answer 12

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

Question 13

Bacillus cereus

Answer 13

Self limiting

Gram positive, spore former

Question 14

The stomach

Answer 14

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

Question 15

Helicobacter pylori - gastric ulcers

Infective cycle

Treatment

Answer 15

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

Question 16

Food associated infections

Answer 16

Mainly spread faeco-orally

Ingestion of contaminated food containing infectious dose of bacteria

Question 17

Diarrhoeal treatment

Answer 17

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

Question 18

Diarrhoeal disease - e. coli

Answer 18

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’

Question 19

Lab detection of E coli

Answer 19

Lactose fermentation

Question 20

E.coli strains - EPEC

Features
Mechanism

Answer 20

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

Question 21

ETEC

Answer 21

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

Question 22

EIEC - enteroinvasive

Answer 22

Invade and destroy epithelial cells

Bloody diarrhoea

Question 23

EHEC

Answer 23

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

Question 24

2011 outbreak: O104:H4

Answer 24

• 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.

Question 25

Shigella

Answer 25

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

Question 26

Salmonella

Answer 26

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

Question 27

S. typhi - typhoid (enteric) fever

Answer 27

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

Question 28

Campylobacter spp.

Answer 28

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

Question 29

Cholera mechanism

Answer 29

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

Question 30

Prevention

Answer 30

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

Question 31

Viral causes of GI-infections

Answer 31

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