GI Infections Flashcards
What defences does the GI tract have against infection
Saliva - bacteriostatic secretions
Gastric acid
Small intestine secretions
Colonic mucus
Anaerobic environment
Flora in gut
What short chain fatty acids do bacteria in the colon produce
Butyrate - energy source for colonocytes. Helps regulate gut environment
Acetate - cholesterol metabolism
Propionate - regulates satiety
What substances are good for the microbiota of the gut and what substances are harmful for it
Good:
- Probiotics - stimulate growth of bacteria in get
- Prebiotics - used as food for microbiota
Harmful:
- Sweeteners - disrupt diversity of microbiota
- Gluten free diet in people without gluten sensivitiy or coeliac disease - decreases number of bacteria species
- Proton pump inhibitors
- Antibiotics
Name some bacterial infections of the GI tract
Salmonella
Campylobacter
Shigella
Enterotoxigenic E. coli
Clostridium difficile
Describe salmonella - what it is, what it does inside the patient and how it spreads
Salmonella is a gram -ve rod
Spread by ingesting contaminated food/water
Is self limiting
Inside gut salmonella gain access to enterocytes -> move to submucosa where the encounter macrophages
Macrophages transfer salmonella to RES where they multiply intracellulary causing lymphoid hypertrophy and hyperplasia
Then re-enter gut from liver/gallbladder
What symptoms do salmonella infections cause
Nausea
Vomiting
Diarrhoea - mostly non-bloody
Fever
Abdominal cramping
Describe camplyobacter, how it causes disease, how it spreads and what its treatment is
Campylobacter is a gram -ve rod - spiral shaped
Spread via faecal-oral route
Releases cytotoxin to cause disease
Treatment - fluids/electrolyte replacement and antibiotics if bloody diarrhoea
What are the symptoms of a camplyobacter infection
Fever
Abdominal cramping
Diarrhoea - can be bloody
Symptoms take a while to appear
Describe shigella, how it causes disease and how it is spread
Shigella is a gram -ve rod. Infection usually resolves within a week
Causes shigellosis - dysentery commonly affecting young children
Spread via infective stools
Shigella invades large intestine colonocytes -> multiplies intracellularly -> invades neighbouring cells
This kills colonocytes and forms abscesses in mucosa
What are the symptoms of a shigella infection
Bloody diarrhoea with mucus
Abdominal cramping
Describe enterotoxigenic E. coli, how it is spread, what symptoms it causes and how it causes disease
ETEC is a gram -ve rod that causes gastroenteritis with symptoms of watery diarrhoea
Spread via faecal-oral route
Common commensual of gut
Invades enterocytes -> produces enterotoxins which cause hypersecretion of Cl -> Na follows -> water follows
What is haemolytic uraemic syndrome and what bacterial infections of the gut can cause it
Haemolytic ureamic syndrome is condition affecting blood and blood vessels. Have destruction of platelets, anaemia and kidney failure due to damage to small vessels of the kidney
Shigella and camplyobacter can cause it
Describe C. diff, how it is spread, how it causes disease and what the treatment is
C. diff is a gram +ve anaerobic, spore forming, bacillus
Minor component of GI flora but can be transferred via faecal-oral route
Following antibiotic therapy, C. diff can colonise the gut and release toxins A and B
Toxin A causes excessive secretion and inflammation
Toxin B is a cytotoxin
Treatment - remove offending antibiotic, fluid resuscitation, metronidazole/vancomycin, probiotics
What are the symptoms of a C. diff infection
Can be asymptomatic
Diarrhoea
Abdominal cramping
What are the causes of viral gastroenteritis
Rotavirus
Norovirus
What are the symptoms of gastroenteritis caused by rotavirus and how are the symptoms caused
Common cause of gastroenteritits in under 5s
Symptoms: vomiting, diarrhoea and fever
Diarrhoea caused by chloride secretoin, SGLT1 disruption and brush border enzyme dysfuction
Treatment is to manage dehydration
Describe gastroenteritis caused by norovius and the symptoms that are seen
Norovirus is most common cause of non-bacterial gastroenteritis
Affects any age due to large number of strains
Infects small intestine and damages microvilli
Symptoms: vomiting, watery diarrhoea and fever
Causes anion secretion (diarrhoea) and delayed gastric emptying (vomiting)
Treatment is oral rehydration
Name some protozoal causes of diarrhoea
Cryptosporidium
Giardia
Entamoeba histolytica
Describe cryptosporidium, how it is transmitted, how it causes disease, the symptoms and treatment for it
Protozoa transmitted via faecal-oral route - can also survive and spread in water
Is caused by ingestion of oocyst containing the parasite which reproduces inside epithelial cells of distal small intestine -> oocysts excreted in faeces to continue cycle
Symptoms of watery diarrhoea (malabsorption and Cl secretion)
Self-limiting
Treatment: supportive but can give anti-parasitic treatment to at risk patients
Describe giardia, how it is spread, how it causes disease, what its treatment is and what symptoms it causes
Protozoal infection causing diarrhoea - common cause of persistant diarrhoea
Spread via faecal-oral route
Symptoms appear after 10+ days: diarrhoea, abdominal cramping
Cyst is ingested -> stomach acid/pancreatic enzymes release parasite -> it multiplies in small intestine - damaged proximal small intestine
Parasite forms a cyst in colon -> excreted to repeat cycle
Treatment - antibacterial and fluid rehydration
Describe entamoeba histolytica, how it is spread, how it causes disease, its symptoms and how it is treated
Protozoal infection with high prevalence in developing countries
Spread via faecal-oral route
Infection follows ingestion of cyst - excystation occurs in colon where trophozoites invade mucosa causing bloody diarrhoea and inflammatory changes
Symptoms: asymptomatic or bloody diarrhoea
May have liver abscess if infection spreads to liver
Treatment is antiprotozoal/metronidazole
What is travellers diarrhoea
Passing 3 or more loose/watery stools
Can have fever and/or abdominal pain
>14 days makes it unlikely to have bacterial cause
Prevention is good hand hygeine and food/water precautions
Which patients have increased risk of travellers diarrhoea
Patients visiting developing countries
Patients dietary exposure
Patients <6yrs
Patients on PPIs
Patients with blood group O
What is the treatment for traveller’s diarrhoea
Mild/moderate = <6stools/24hrs. Treatment is hydration and antidiarrhoeal agents
Severe = >6stools/24hrs. Treatment is IV fluids and antibiotics if appropriate
