9.1 GI Infections Flashcards
What sort of toxins can the gut be exposed to?
- Chemical
- Bacteria
- Viruses
- Protozoa
- Nematodes (Roundworms)
- Cestodes (Tapeworms)
- Trematodes (Flukes)
What are commensal bacteria?
Make up part of the normal gut flora, have a role in protecting the gut against pathogenic bacteria, viruses and protozoa
What are GI protective mechanisms?
- Sight, smell, memory
- Saliva (bacteriostatic secretions)
- Gastric acid (acidic environment)
- Small intestinal secretions (Bile)
- Colonic mucus (protects from commensal bacteria)
- Anaerobic environment (small bowel, colon)
How does the amount of commensal bacteria change along the gut?
More bacteria present the further along length of gut.
Why is the stomach described as a microaeriophilic environment?
Decreased partial pressure of oxygen but not an anaerobic environment
Describe the environment of the colon
Anaerobic environment
Large gut micro biome
What are the benefits of the micro biome?
- Harmful bacteria cannot compete for nutrients (outcompeted by gut microbiome) and cannot multiply and colonise
- Microbiome produces antimicrobial substances
- Helps to develop newborn’s immune system
- Produce certain nutrients (Vit K)
Poor microbiota diversity increases risk of :
Obesity
Inflammatory bowel disease
Poor response to chemotherapy
Poor response to insulin
What do bacteria in the colon produce?
SCFA (acetate, propionate, butyrate)
What is the function of butyrate?
energy source for colonocytes
helps regulate gut environment
What is the function of acetate?
Involved in cholesterol metabolism
What is the function of propionate?
Helps regulate satiety
How might fibre intake influence our health?
High fibre diet = binds bile salts, more bile excreted, more cholesterol used to produce new bile salt, lower levels of cholesterol. Influences composition of gut microbiota (probiotic)
What is a probiotic?
A substance that encourages the growth of our gut micro biome by introducing live bacteria and yeasts delivered in food.
How do sweeteners affect our micro biome?
Disrupt diversity of microbiota
What influence does a gluten free diet have on people without gluten insensitivity/coeliacs disease?
Negative effect as lowers number of key species of gut microbiota
Help tighten tight junctions, reducing leaky gut, cant absorb some larger nutrient molecules
How do proton pump inhibitors influence the gut microbiome?
Stop acid production, stopping our innate protection. Increases risk of GI infections and disrupting the microbiota
Why is consuming antibiotics within meat harmful?
Disrupts gut microbiome, linked to obesity
What are prebiotics?
Essentially food for the existing microbiota (accessible carbs and fibres - indigestible for us)
What is a faecal microbiota transplant?
Take faeces from healthy donors and give to patients with poor gut health.
How is pseudomembraneous colitis treated?
Faecal enemas
What infection commonly causes pseudomembraneous colitis?
Clostridium difficile
What are the possible routes of transmission of faecal microbiota transplant?
- NG/duodenal tubes (unappealing for most patients)- Can be done under anaesthetic
- Upper GI endoscopy
- Colonoscopy
- Transplant can be put in Caecum (allowed to move throughout colon) - Distributed throughout length of colon
What are successful uses of faecal microbiota transplant?
Pseudomembraneous colitis
Clostridium difficile
IBD
Crohn’s disease
Why is a faecal microbiota transplant preferable to antibiotic treatment of clostridium difficile?
Up to 90% resulting of diarrhoea following FMT (30% in vancomycin treatment)
No negative side effects
No antibiotic resistance
What criteria makes someone a suitable donor for faecal microbiota transplant?
10-25 year olds
Donors have not used antibiotics, laxatives or diet pills in last 3 months
Do not have GI disease
Completely screened (inflammatory markers, Hepatitis, HIV)
How is a stool sample processed for FMT?
From a suitable donor
Fresh stool to transplantation or storage ( 1 hour)
Stool centrifuged filtered and diluted
What gram negative rod bacteria can infect the gut?
- Salmonella
- Campylobacter
- Shigella
- Enterotoxigenic E-coli
What gram positive bacterium can infect the gut?
Clostridium difficile
What are the symptoms of a GI infection with salmonella?
Nausea, vomiting and diarrhoea (mostly non-bloody), fever, abdominal cramping
What is the main transmission route of salmonella?
Spread by ingesting food and water contaminated by salmonella bacteria
How long does it take to become symptomatic after being infected with salmonella?
48 hours
Describe the infective process of salmonella
Ingested salmonella bacteria must travel through stomach to small intestine
Enter small intestinal cells by endocytosis
Pass through to submucosa and taken up by macrophages
Carried to reticuloendothelial system
Multiply intracellularly, causing lymphoid hyperplasia and hypertrophy
Salmonella reenter bowel via the liver and gallbladder
How is salmonella usually treated?
In healthy individual usually self-limiting (2/3 days)
Fluid resuscitation
What is campylobacter?
A spiral or s shaped gram negative organism. Mainly microaerophilic
What is the route of transmission of campylobacter?
Falcon-oral route
From ingestion of poultry faeces ( lots of campylobacter in poultry GI tract )
How long does it take to be symptomatic with a campylobacter infection?
Longer incubation period (1-7 days)
What are symptoms of an infection of campylobacter?
Fever, abdominal cramping, perfuse diarrhoea (can be bloody)
How does campylobacter cause its effects?
Must pass through the stomach to infect the small intestine
Release cytotoxin similar to cholera
What is the treatment for campylobacter infection?
- Fluid/electrolyte replacement
- Consider antibiotics if bloody diarrhoea
Generally self limiting and lasts days to week
Where does campylobacter colonise to cause bloody diarrhoea?
The colon
Who does shigella infection commonly affect?
Commonly affects young children under 5 years of age
What is a dysentery?
Any of several inflammatory disorders of the intestines, especially of the colon, characterised by abdominal pain, fever and severe diarrhoea often with blood and mucus in the stool.
How does shigella spread?
Only needs small dose to infect
- ingesting infected food/water
- person to person (sometime flies)
Describe the pathology of shigella?
Ingested shigellae invade large intestine colonocytes via endocytosis
Escape from endocytic vesssels
Replicate intracellularly
Invades neighbouring cells
Mucosal abscess forms as the cells in the colon die
What are symptoms of shigella?
Bloody diarrhoea with mucus and abdominal cramping
How long does a shigella infection last?
Resolves in a week
What is enterotoxigenic e-coli?
A gram negative rod bacterium that is a commensal of the colon but can also be a pathogen
How does enterotoxigenic e-coli spread?
Spread by faecal oral route in contaminated water
What is a common cause of travellers diarrhoea?
Enterotoxigenic e-coli
What is the pathology of the enterotoxigenic e-coli?
Invades small intestine and adheres to the enterocytes.
Produces enterotoxins
Cause hypersecretion of chloride ions from enterocytes
Sodium ions follow into gut lumen
Water move into gut lumen
What are enterotoxins?
Proteins produced by bacteria that is toxic to enterocyte
What is the main symptom of entertoxigenic e-coli infection?
Perfuse diarrhoea
Which infections of the GI produce bloody diarrhoea and why?
Shigella and campylobacter as involve infection of the large intestine.
Which GI infections cause watery diarrhoea?
Enterotoxigenic e-coli
Salmonella
What is haemolytic uraemic syndrome?
Triad of anaemia, thrombocytopenia and AKI
Which GI infection can cause haemolytic uraemic syndrome?
Shigella
Campylobacter
Why are antibiotics only prescribed in serious cases of GI infection?
Antibiotic resistance
How does duration of infection vary in GI infections?
Enterotoxigenic e-coli
Salmonella (days)
shigella (week)
Campylobacter (weeks)
Which gram negative rod is most likely to cause bloody diarrhoea?
Shigella
What is clostridium difficile?
Gram positive, anaerobic spore forming bacillus
How is clostridium difficile spread?
Minor component of GI tract
Faecal-oral route
Why is clostridium difficile easily spread?
As produce spores that are very hard to get rid of
What commonly causes a c-difficile infection?
Happens following antibiotic therapy (broad spectrum)
Antibiotics disrupt normal gut microbiota allowing c-diff to colonise gut
What happens when clostridium difficile colonises the gut?
Releases toxins A and B into the epithelial cells oft he colon
What is the function of the toxins released by clostridium difficile?
Toxin A = enterotoxins that results in excessive secretion and inflammation (causes diarrhoea)
Toxin B = cytotoxin (kills colonocytes)
How does a clostridium difficile infection present in patients?
- mostly asymptomatic
- varying degrees of diarrhoea (mild to terrible, usually non-bloody)
- abdominal cramping
What are rare complications of clostridium difficile?
Pseudomembraneous colitis Toxic megacolon (surgery needed)
What is toxic megacolon?
Massive dilation of the colon
Needs surgery to remove before perforation and causing peritonitis
What is pseudomembraneous colitis?
Inflammatory condition, characterised by elevated yellow plaques joining in the lumen of the colon to form a pseudomembrane
What is the treatment of clostridium difficile?
- Remove offending antibiotic
- Fluid resuscitation
- Metronidazole/Vancomycin - ABX to treat c-diff
- Probiotics
What are 2 viral causes of gastroenteritis?
Rotavirus
Norovirus
What are 3 parasitic causes of gastroenteritis?
Cryptosporidium
Giardiasis
Entamoeba
What is a common cause of gastroenteritis in under 5s?
Bacterial - shigella
Viral - rotavirus
Who is most commonly affected by rotavirus?
Children under 5
Adults reparable you affected as have immunity
How does rotavirus spread?
Small dose via faecal-oral route
What are the first symptoms of rotavirus?
Vomiting with a fever Diarrhoea follows (lasting up to a week)
Why does diarrhoea occur in rotavirus?
Chloride secretion, resulting in Na movement into lumen. Water follows.
SGLT1 disruption resulting in malabsorption, Mose sodium and glucose in the gut lumen exerting an osmotic pressure and drawing water out of colonocytes
Reduced brush border enzyme function, molecules aren’t broken down and absorbed. Stay in gut lumen and exert an osmotic pressure
What is the treatment of rotavirus?
Managing dehydration due to fluid loss
How is SGLT1 disrupted in rotavirus?
SGLT1 function reduced
Reduced movement of Na/glucose into enterocyte
Higher osmotic load in gut
Water moves into gut via osmosis
Why is there malabsorption in rotavirus?
As there is brush border dysfunction
What is the most common cause of non bacterial gastroenteritis?
Norovirus
What is Norwalk virus?
Norovirus
How contagious is norovirus?
Highly contagious, only requires small dose (18 particles) and resistant to cleaning
How is chloride secretion affected in rotavirus infection?
Rotavirus causes an increase in cAMP within the enterocyte
Stimulates opening of the CFTR channels
Chloride ions are released into the lumen of the gut
Why does rotavirus predominantly affect young people whilst norovirus affects any age?
Rotavirus - develop immunity, rare in adults
Norovirus - dont develop immunity due to huge number of strains, can affect people at any age
What structures are affected in a norovirus infection?
Enterocytes of the small intestine. Damages microvilli (brush border enzyme disruption)
How long does norovirus last?
1-4 days
What are the symptoms of norovirus?
Vomiting, watery diarrhoea, fever
- anion secretion
- vomiting due to delayed gastric emptying
What is the treatment for norovirus?
Oral rehydration therapy
What are the 3 Protozoa that can cause gastroenteritis?
Cryptosporidium
Giardiasis lamblia
Entamoeba
What type of Protozoa is cryptosporidium?
A sporozoan
- non-motile
What type of Protozoa is giardia lamblia?
A flagellate
- move by rotating a whip like flagella
What type of Protozoa is entamoeba?
Amoeba
- move by extending cytoplasmic projections
How is cryptosporidium transmitted?
Faecal-oral route
Bodies of water infected by animal faeces
Who are commonly affected by cryptosporidium?
- People who swim regularly in pools with insufficient sanitation (certain strains of Cryptosporidium are chlorine-resistant)
- Child-care workers
- Parents of infected children
- People caring for other people with cryptosporidiosis
- Backpackers, hikers, and campers who drink unfiltered, untreated water
- Petting Farms and open farms with public access
- People, including swimmers, who swallow water from contaminated sources
- People handling infected cattle
- People exposed to human faeces
Describe the infective cycle of cryptosporidium
- Disease caused by ingestion of an oocyst (a cyst containing parasite)
- Reproduces in epithelial cells of distal small intestine
- Oocyst excreted in faces to continue cycle
What are the symptoms of cryptosporidium infection?
Watery diarrhoea
- Malabsorption (brush border enzymes affected)
- Chloride secretion
How is cryptosporidium infection treated?
Normally self limiting - supportive treatment with fluids
Occasionally anti-parasitic treatment in at risk groups (AIDS patients)
What are the symptoms of giardia lamblia infection?
Usually asymptomatic If symptomatic (appear after 10+ days incubation period) • Diarrhoea • Abdominal cramping • Can last up to 6 weeks Symptoms more common in children Common cause of persistent diarrhoea
How is giardia lamblia spread?
Faecal oral route. Water supplies often affected in developing countries.
- swimming
- eating uncooked contaminated food
- direct contact
- drinking contaminated water
- travelling to countries where giardiasis is common
Describe the life cycle of giardia lamblia
- Cyst is ingested
• Stomach acid/ pancreatic enzymes release parasite from cyst which then multiplies in small intestine- incubation 1-2 weeks
• Damages proximal small intestine causing symptoms (diarrhoea)
• Villous atrophy occurs - Parasite then goes back into cyst stage in colon, excreted to repeat the cycle
How do we treat giardia lamblia infection?
Antibiotics
Fluid rehydration therapy
What symptoms can occur post giardia lamblia infection?
Lactase deficiency resulting in lactose intolerance
Where is entamoeba histolytica commonly seen?
In developing countries
How does infection with entamoeba histolytica present?
Asymptomatic (80%)
If symptomatic = diarrhoea and very rarely liver abscesses
How is entamoeba histolytica transmitted?
Faecal-oral route (contaminated food or water)
Who does entamoeba histolytica commonly affect?
- travel to tropical places with poor sanitary conditions
- live in institutions with poos sanitary conditions
- men who have sex with men
Describe the infective cycle of entamoeba histolytica
- Ingestion of cyst
- Excystation occurs in colon where trophozoites invade mucosa
- Bloody diarrhoea and inflammatory changes occur (similar to IBD)
- Infection can also spread to liver (abscesses form)
- Cysts then pass out with faeces- infect others
What is the treatment of entamoeba histolytica?
- Anti-protozoals/metronidazole
* Severe colitis/toxic megacolon may require surgery
What is the most common cause of travellers diarrhoea?
Enterotoxic escherichia coli
What are the symptoms of travellers diarrhoea?
Passing 3 or more loose watery stools
May have fever and abdominal pain
What does symptoms of travellers diarrhoea for greater than 2 weeks suggest?
That the cause is not bacterial
What are the risk factors for getting travellers diarrhoea?
Place you are visiting Dietary exposure Less than 6 years old PPIs Blood group O
How do we prevent travellers diarrhoea?
Good hand hygiene
Food and water precautions
How do we treat travellers diarrhoea?
Mild/moderate (less than 6 stools/24 hrs)
• Hydration (oral rehydration solutions/ safe water)
• Antidiarrhoeal agents
Severe (more than 6 stools/24 hrs)
• IV fluids (potentially)
• Antibiotics (if appropriate)
