Wk 3 - Symposium 3 (Clinical): GI Infections Flashcards
(41 cards)
What are the two classifications of gastro-intestinal/intra-abdominal infections?
- Intra-luminal: Usually due to ingestion of a exogenous pathogen (non-commensal) e.g. Infective gastro-enteritis
- Extra-luminal: Usually due to introduction / spillage of endogenous normal gut commensal flora into extra-luminal site. e.g. Intestinal perforation – peritonitis, Intra-abdominal abscesses, Blocked biliary tree: cholangiitis, liver abscesses
List some of the GI tract’s defences against infection.
- Mouth and oesophagus: flow of liquids, saliva, lysozyme, normal flora
- Stomach: acidic pH
- Small intestine: Flow of gut contents, peristalsis, mucus, bile, IgA, lymphoid tissue (Peyer’s patches), shedding and replacement of epithelium, normal flora
- Large intestine: Normal flora, peristalsis, shedding and replication of epithelium, mucus
Describe the different pathogenetic mechanisms of enteric bacteria.
Most GI pathogens clinically manifest in a very similar way…
- Diarrhoea (watery of blood)
- Vomiting
- Abdominal pain and tenderness
- with or w/o fever
How is diarrhoea classified?
- Community-acquired: Presenting with diarrhoea in community or within first 72hrs of admission
- Hospital (nosocomial)-acquired: Presenting with diarrhoea >72hrs after admission to hospital
Diarrhoea can be ____ or ____.
Diarrhoea can be secretory or inflammatory.
How does a child with infantile diarrhoea present clinically?
- Listless, irritable child. Poor feeding
- Watery stool (no blood)
- Failure to thrive
- May progress to severe dehydration
What agents usually cause infantile diarrhoea?
- Viruses: Rotavirus, Adenovirus
- Bacteria: Enteropathogenic Escherichia coli (EPEC) [destroy microvilli]
How does a patient with travellers diarrhoea present clinically?
- Watery diarrhoea, malaise
- 5-15d after arrival in foreign country
- Self-limits in 1-5d
- 20-50% have illness >5d
What pathogens usually cause travellers diarrhoea?
- Minority be due to agents such as cholera, salmonella, shigella, amoebas but most >50% are due to:
- Enterotoxigenic Escherichia coli (ETEC) strains
- Heat-labile and heat-stable toxins.
What is cholera?
- Vibrio cholerae
- Curved Gram negative rod. Salt-tolerant.
- Toxin mediated illness- A/B subunit toxin binds to enterocyte and causes irreversible activation of adenyl cyclase » inhibition of Na+ and Cl- uptake » excretion of H20 » DIARRHOEA+++
List the two strains of cholera that cause disease.
O1 and O139 strains toxigenic and cause disease
How does a person with cholera present clinically?
- Abrupt onset of profuse watery diarrhoea (rice water stool). Fever unusual.
- Dehydration kills: can lose up to 1 litre fluid/hr.
What is Cryptosporidium?
- Protozoan - a microscopic parasite that causes the diarrheal disease cryptosporidiosis. Both the parasite and the disease are commonly known as “Crypto.”
- Faecal-oral. Ingestion of 1-5 oocysts enough.
- Oocysts highly resistant to disinfectants
- Waterborne > person to person
- Worldwide (including UK)
What are the main toxins causing community-acquired secretory diarrhoea?
- Staphylococcus aureus
- Bacillus cereus
- Clostridium perfringens
- Algal food poisoning (dinoflagellates): shellfish
What is the most common cause of inflammatory diarrhoea (in the UK)?
Campylobacter jejuni
Curved (seagull shaped) Gram-negative rods
Commonest bacterial gastro-enteritis in UK
What is one post-infectious complication of campylobacter?
Guillian-Barre Syndrome
What are the two different types of salmonella infections?
-
Non-typhoidal / “food poisoning”
- Worldwide, incl UK
- Rare systemic infection
- Antibiotic treatment sometimes required
-
Typhoidal / enteric fevers
- Tropical, imported infections
- Always involve systemic infection
- Antibiotic treatment always required
In typhoid (enteric fever caused by salmonella typhi and paratyphie), patients are more likely to present with ____ than ___ (diarrhoea/constipation).
In typhoid (enteric fever caused by salmonella typhi and paratyphie), patients are more likely to present with constipation than diarrhoea.
What is the most common strain of VTEC E.coli?
E. coli O157 most common VTEC strain.
In E.coli infections, antibiotics may…
Antibiotics may worsen the situation –> result in increase toxin release
The most common cause of hospital-acquired diarrhoea is…
Clostridium difficile
Describe the pathophysiology of Clostridium difficile infection (CDI).
1) Broad-spectrum antibiotic administration
2) Abolition of “colonisation resistance”
3) Ingestion of C.difficile spores from the environment (may be endogenous in some patients)
4) Spore germination in GI tract
5) Growth and proliferation of C.difficile bacilli
6) Toxin production. Trigger for this unknown- ?stress response/ nutrient depletion or cell-cell signalling (quorum sensing)
7) Toxin binding to colonic mucosa- resulting inflammation can range from mild to severe (colitis)
8) Diarrhoea results in massive spore release into environment
_____ precipitate Clostridium difficile infections.
Antibiotics precipitate Clostridium difficile infections.
