Bacterial and Viral Infections of the GI tract Flashcards
How can GI pathogens damage the body?
- Local inflammation
- Ulceration / perforation of mucosal epithelium
- Disruption of normal gut microbiota
- Pharmacological action of bacterial toxins
- Invasion into blood or lymphatics
What can happen as a result of a ruptured / perforated ulcer?
- May result in leaking of food and gastric juices to the peritoneal or abdominal cavities
- Treatment requires surgery
What can happen to the villi as a resultof E. coli invasion?
Vilous atrophy
What are the stools like of someone affected by EPEC and cholera?
Watery
What bacterial infections can cause bloody stools?
Campylobacter and Shigella
Give some examples of bacterial diarrhoeal pathogens?
- Vibrio cholerae
- Escherichia coli
- Campylobacter jejuni
- Salmonella spp.
- Shigella spp
- Listeria monocytogenes
What are the features of V. cholerae?
- Gram negative
- Comma-shaped rod
- Flagellated
- Charecterised by epidemics and pandemics
- Human-only pathogen
- Flourishes in communities with no clean drinking water / sewage disposal
How can V. cholerae be desifered?
Based on O antigens
- O1: Associated with early pandemics
- Non-O1: 0139 associated with recent outbreaks
What are the 2 types of V. Cholerae vaccines?
- Parenteral vaccine: low protective efficiency
- Oral vaccine: effective and suitable for travellers
How infective is V. Cholera and how does it infect humans?
- Only infective in large doses
- Many organisms killed in stomach
- Colonisation of SI involving flagellar motion, mucinase, attachement to specific receptors
How do the V. cholerae cause diarrhoea?
- Produces multicomponent toxin - CTx
- Causes a massive increase of cAMP opening CFTR
- Opening CFTR causes Cl- to move out of cell
- Causes loss of fluid and electrolytes without damage to enterocytes
Describe the Cholera Toxin (CTx)
- Oligomeric complex of 6 protein subunits
1 copy of A subunit (enzymatic)
5 copies of B subunit (receptor binding)
How much fluid is lost as a result of cholera infection and what does this result in if untreated?
- 1 litre / hour
- Electrolyte imbalance leading to dehydration, metabolic acidosis and hypokalemia
- Hypovolemic shock
What is the mortality rate of cholera infection?
- 40 - 60%
- <1% mortality if given fluid / electrolytes (ORT)
How would you describe stool from a patient with cholera?
Rice Water stool - completely fluid, no blood, mucous can be present
Describe the features of E. coli?
- Gram negative
- Bacilus
- Member of normal GI microbiota
- Can be resistant to acid
- Some strains possess virulence factors enabing them to cause disease
What are the types of E. coli causing GI infections?
- EPEC - enteropathogenic
- ETEC - enterotoxigenic
- VTEC/STEC - verocytotoxin-producing
- EHEC - enterohaemorrhagic
- EIEC - enteroinvasive
- EAEC - enteroaggregative
What E. coli strain is known for causing travellers diarrhoea
ETEC (occurs in 20 - 50% of travellers)
What E. coli infection has sporadic cases and outbreaks of infection in under 5’s?
EPEC
What strain of E.coli is a food-borne infection in areas of poor hygiene?
EIEC
What bacteria creates a pedestal formation?
E. coli
What is an endotoxin?
It is actually part of the bacteria
What is an exotoxin?
Secreted by the bacteria
What does the heat-labile (LT) toxin produced by E. coli cause an increase in?
cAMP and secretion
What does the heat-stable toxin (STa) produced by E. colicause an increase in?
cGMP and secretion
What bacteria is often found in undercooked chickens and the most common cause of diarrhoea in the UK?
Campylobacter jejuni
Desribe the features of C. jejuni?
- Gram negative
- Helical bacillus
- Large animal reservoir
- Causes food-associated diarrhoea
- Mucosal inflammation and fluid secretion
Describe the affect of C. jejuni infection on the SI from a histological point of view?
- Inflammation involves entire mucosa
- Vilous atrophy
- Necrotic debris in crypts
- Thickening of basement membrane
What are the features of Salmonella spp?
- Gram negative
- Bacilli
How many serotypes of Salmonella spp are there?
> 2000 serotypes
How is Salmonella spp transmitted?
- Consumption of raw / undercooked meat, contaminated eggs and milk
- Secondary spread can be human-human
- Ingestion of large numbers of Salmonella to cause infection
What are some important Salmonella species?
- S. typhi
- S. paratyphi
- S. enteritidis
How does salmonella cause diarrhoea?
- Large numbers of salmonella bacteria ingested
- Absorption to epithelial cells in terminal section of SI
- Penetration of cells and migration to lamina propria
- Multiplication in lymphoid follicles
- Inflammation response mediates release of prostaglandins
- Stimulation of cAMP
- Release of fluid and electrolytes causing diarrhoea
What cac S. typhus and S. paratyphus cause?
- Enteric fevers: typhoid and paratyphoid
- Systemic infections initiated in GI tract
- Restricted to humans
What cells do S. typhi and paratyphi bacteria multiply and transport themsleves in?
Macrophages
How long can S. typhi stay in the stools for in patients with Typhoid fever?
Several weeks after recovery
How often often can S. typhi become a chronic infection in the body?
1-3% of the time, more common in women and the elderly
Name a notifiable disease
Typhoid fever (S. typhi)
What are the spots called that present on those with typhoid fever?
Rose spots
What are the 2 types of Typhoid vaccines?
- Oral; live attenuated booster needed after 5 years -Parenteral; capsular polysaccharide booster after 2 years - 50 - 80% effective - Recommended for travellers to endemic areas
What is the shape of Shigella spp?
- Bacillus
What does shigella spp. cause?
Shigellosis (bacillary dysentary) spread via human to human
What are the 4 species of Shigella spp?
- S. dysenteriae: most serious
- S. flexneri: sever disease
- S. boydii: severe disease
- S. sonnei: mild infections
Describe the pathogenesis of Shigella infection?
- Attaches to mucosal epithelium of distal ileum and colon
- Causes inflammation and ulceration
- Rarely invasive
- Produces Shiga toxin (STx)
- Diarrhoe watery initially, later cacn contain blood and mucous
- Usually self-limiting
Describe the shape of L. monocytogenes
Coccobaccillus
What does L. monocytogenes cause?
Listeriosis usually presents as meningitis
How many organisms are needed to cause listeriosis?
< 1000
What populations are at risk of Listeiosis?
- Pregnant
- Immunosuppressed individuals
What causes listeriosis?
- L. monocytogenes
- Can be present in pate, soft cheese, unpasteurised milk, humus
Name 3 viruses which can cause diarrhoea
- Rotavirus
- Noravirus
- Enteric adenovirus
Desribe the structure of rotavirus
- ‘rota’ - wheel
- 11 seperate segments of double-stranded RNA
Who is affected by rotavirus?
- Many mammals
- Most common in children < 2 years old
How is Rotavirus transmitted?
- Faeco-oral, but may also be faeco-respiratory
- As few as 10 ingested particles can cause disease
- It is a seasonal occurance
Describe the pathogenesis of rotavirus infection?
- Incubation period of 1-2 days
- Replication of virus in SI epithelial cells at tips of villi
- Results in villous atrophy
- Damage caused to infected cells leaving immature cells with reduced absorptive capacity for sugar, water and electrolytes
- Onset of vomitting, diarrhoea lasting 4 - 7 days
How many rotavirus particles are released per gram of faeces?
Up to 10^10 - 10^11
What virus causes the majority of sickness and diarrhoea outbreaks worldwide?
Norovirus
What percentage of adults have had norovirus at some point in their lives?
60%
How is norovirus transmitted?
- Human only pathogen
- Transmission is faeco-oral, contaminated water / shellfish, fomites
- < 100 virons can cause infection
What percentage of community-acquired diarrhoeas in young children are caused by enteric adenovirus?
10%
What is antibiotic-associated diarrhoea?
- Does not involve ingestion of pathogen or toxin
- Can arise from disruption of gut microbiota following antibiotic therapy
What bateria can overgrow in the gut as a result of tetracycline antibiotic therapy?
Allows colonisation by Staphylococcus aureus and candida sp.
What antibiotic suppresses the gut microbiota and allows Clostridium difficile to multiply?
Clindamycin
C. dificile is now associated with resistance to what antibiotic?
Vancomycin
How does C. difficle survive harsh conditions?
the production of spores - produces an enterotoxin and cytotoxin
Desribe the structure of Helicobacter pylori?
- Gram negative
- Spiral
- Flagellated
- Microaerophilic
- > 80% infected individuals are asymptomatic
What diseases can H pylori cause?
- Duodenal ulcers
- Gastric ulcers
- GORD
- Non-ulcer dyspepsia
What are the key features of H pylori?
- Acid-inhibiting protein - survival in stomach
- Urease - neutralisation of acid pH
- Adhesins - ninding to gastric epithelium
- Cytotoxin - damage to gastric epithelium
- Flagellum - movement through gastric mucus layer
How is H pylori associated Gastritis treated?
- 1 week (7 days) triple therapy EITHER - PPI + clarithromycin + amoxycyillin OR - PPI + clarithromycin + Metronidazole
What is food poisoning?
Syndrome is restricted to diseases caused by toxins elaborated by contaminating bacteria in food before it is consumed
What are examples of toxins?
- Emetic toxins of Bacillus cereus
- Enterotoxin of Staphylococcus aureus
- Neurotoxin of Clostridium botulinum
What can Bacillus cereus be found in?
Rice
How does clostridium perfringens cause disease?
- Usually caused by type A strains from animal guts and soil
- Contamination of raw meat products
- Spores survives cooking and germination takes place
- Multiplication in large intestine, production of spore and enterotoxin
- Damage to intestinal epithelium
- Diarrhoea
What is Oral Rehydration Therapy?
- Involves the replacements of fluids and electrolytes lost during diarrheal illnes
- 90 - 95% of cases of acute diarrhoea can be successfully treated with an oral rehydration solution (ORS)
- ORS increases the resorption of fluids and salts into the intestinal wall
