Bacteria affecting the GIT

Question 1

Define Gastroenteritis

Answer 1

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

Question 2

Define 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

Define 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

Define Enterocolitis

Answer 4

Inflammation of mucosa of small and large intestine

Question 5

Defences of the mouth?

Answer 5

Flow of liquids
saliva
lysozyme
normal bacterial flora

Question 6

Defences of the oesophagus?

Answer 6

flow of liquids

peristalsis

Question 7

Defences of the stomach?

Answer 7

Gastric Acid pH 1-2

Question 8

Defences of the small intestine?

Answer 8

flow of gut contents
peristalsis
mucus, bile
secretory IgA
lymphoid tissue
shedding and removal of epi

Question 9

Defences of the large intestine?

Answer 9

Normal flora
peristalsis
shedding and replication of epi
mucus

Question 10

What is food poisoning?

Answer 10

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

Question 11

Staphylococcus aureus in food poisoning?

Answer 11

Growth in food after human contamination> mainly dairy, cooked meats
50% of strains produce heat stable enterotoxins - resistant to stomach acid and digestive enzymes
3-6hrs of severe vomiting
Complete recovery

Question 12

Botulism: Clostridium botulinum in food poisoning?

Answer 12

Heat stable toxin ingested in food, leads to flaccid paralysis and death
Infant botulism most common

Question 13

What is bacillus cereus in?

Answer 13

Fried rice - gram positive, heat resistant spore former

Question 14

What bacteria infects the lower GIT?

Answer 14

Ones that resist the low pH of the stomach

Question 15

What causes gastric ulcers?

Answer 15

Helicobacter pylori

Question 16

How is helicobacter pylori resistant to stomach acid?

Answer 16

Produces urease - turns urea to ammonia and co2
= Protective cloud during transit to gastric mucin layer
Ammonia basis of breath test

Question 17

How to treat diarrhoea?

Answer 17

Fluid and electrolyte replacement

Antibiotic treatment often not successful and may worsen problem

Question 18

Why may antibiotic treatment worsen diarrhoea?

Answer 18

They wipe out competing organisms or stimulates toxin production

Question 19

Diarrhoea - E.coli features?

Answer 19

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 20

How to detect E.coli?

Answer 20

Lactose fermentation - MacConkey agar

PCR/antigen tests for serotypes

Question 21

EPEC features?

Answer 21

Bundle-forming pili important in attachment
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 22

How does ETEC work?

Answer 22

Attach via adhesive pili

Produce Heat Stable (ST) and Labile (LT) enterotoxins (cholera like) that cause diarrhoea

Question 23

What does ETEC commonly cause?

Answer 23

Travellers diarrhoea OR Delhi Belly! (No blood) (cholera like in some cases)

Question 24

What does EIEC do? What does it cause?

Answer 24

Invade and destroy epithelial cells

Causes bloody diarrhoea

Question 25

EHEC features?

Answer 25

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 26

Shigella features?

Answer 26

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 27

Salmonella features?

Answer 27

Historically most common food-associated pathogen in UK- FORMER NO.1 CAUSE IN UK Spread from food- mainly chicken and dairy products, but also person to person 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 28

Lab detection of salmonella?

Answer 28

MacConkey agar | Non-lactose fermenter

Question 29

S.typhi features?

Answer 29

Cause of typhoid fever Infection initiates in the intestine Spreads systemically- transported in macrophages around body seed many organs before further spread causes increasing fever over 14 days >> GI symptoms Pre-antibiotics 12-16% died Complications: GI lesions and haemorrhage toxaemia- endocarditis Meningitis Vi antigen vaccine recommended for travel 1 – 3 % become carriers >> gall-bladder

Question 30

What is the number 1 cause of food poisoning in the UK?

Answer 30

Campylobacter spp.

Question 31

Campylobacter spp. features? (also known as helicobacter pylori)

Answer 31

Gram-negative micro-aerophiles Campylobacter jejuni most common Acquired by ingestion of contaminated food Major reservoir in Chickens> 75% of all we buy have colonisation Symptoms like Shigellosis and Salmonellosis: - ulceration (jejunum), diarrhoea up to 10 movements per day… - longer lasting illness- up to 3 weeks! - complications: Guillame Barre and reactive arthiritis

Question 32

What is the number 1 cause of food poisoning worldwide?

Answer 32

Cholera

Question 33

What causes cholera?

Answer 33

Caused by motile Gram-negative comma-shaped bacterium

Question 34

Cholera prevalence?

Answer 34

Estimated 1.3-4 million cholera cases and 21000–140 000 deaths due to cholera every year- mainly developing countries

Question 35

How does the cholera toxin work regarding water flow?

Answer 35

ADP-ribosylation of G-protein signalling pathways causes increased secretion of Chloride ions This prevents influx of Sodium ions into cells Results in rapid loss of water from tissue- massive diarrhoea = rapid fluid loss of 1-3 litres per hour

Question 36

How to treat cholera?

Answer 36

Rapid fluid and electolyte replacement required or dehydration and death result

Question 37

Symptoms of cholera when severely dehydrated?

Answer 37

``` Unconscious, floppy Sunken and dry eyes Absent tears V dry mouth and tongue Drinks poorly or cannot drink Skin pinch - goes back very slowly ```

Question 38

How to prevent cholera?

Answer 38

Unsuccessful vaccine | Improve water system and sanitation

Question 39

Where are viral causes of GI infections most likely? How are they spread?

Answer 39

Developing countries | Mainly oral-fecal spread

Question 40

Rotavirus features?

Answer 40

``` Wheel-like viral particle Diarrhoea caused by tissue damage in small intestine Dehydration main risk Very low-infectious dose Very contagious V resistant to celaining products ```

Question 41

Winter virus features?

Answer 41

Norovirus (Norwalk viruses) - not cultivated Chills, headache, fever, nausea, vomiting, v-low infectious doses (10). recovery in 24 – 48 hours Common in hospital settings …. Hard to clean away

Question 42

How is the cholera toxin produced?

Answer 42

Vibrio cholerae ingested Large doses needed to cause disease unless on antibiotics and acholorhydric Sensitive to stomach acid Small intestine colonisation depends on: motility, production of mucinase attachment to specific receptors Toxin production Massive loss of fluid and electrolytes