GI Tract Infections Flashcards
(35 cards)
What are GI infections?
Gastrointestinal infections are viral, bacterial or parasiticinfections that cause gastroenteritis, an inflammation of thegastrointestinal tract involving both the stomach and the smallintestine
What is the GI tract?
Begins at the oral cavity, the mouth and ends at the anus.
- A diverse community of microorganisms comprise and define theintestinal microbiota.
- The intestinal microbiota contributes to maintaining stability andpreventing overgrowth or infection with pathogenic bacteria.
- Disruption of this stability results in susceptibility to infection.
- Ingestion of pathogens can cause many different infections
What is the bodies defence mechanism?
Mechanical movement (peristalsis) throughout GI tract.
● Mucus/bile – physical barrier preventing attachment to epithelial cells, mucuscontains IgA antibodies.
● Lysozyme – enzyme digests bacterial cell wall.
● Acid pH.
● Shedding and replacement of epithelium.
● Normal flora
Facts about GI infections?
17mil cases per year world
3-6 mil children die
>26 bil in developing world.
Symptoms of GI Infections
Diarrhea
Vomiting
fever
Loss of appetite
Headache
Blood/mucus in stool
Common causes of GI infection
Viral - norovirus/rotavirus
Bacterial - e.coli, salmonella, c.diff, helicobacters
Parasitic - giardiasis, cryptosporidiosis
Gastroenteritis meaning
a syndrome characterised by gastrointestinal symptoms including nausea, vomiting, diarrhea and abdominal discomfort
Dysentery meaning
an inflammatory disorder of the gastrointestinal tract often associated with blood and pus in the faeces and accompanied by symptoms of pain, fever, abdominal cramps; usually resulting from disease of the large intestine
Enterocolitis meaning
inflammation involving the mucosa of both the small and large intestine.
What is
Escherichia coli
Although E. coli is part of the normal flora, some strains can cause enteritis by a variety ofmechanisms.
❖ Can cause severe stomach cramps, bloody diarrhea and vomiting.
❖ There are four main types of enteropathogenic
E. coli, which cause enteritis.
Enteropathogenic E. coli (EPEC).
Enterotoxigenic E. coli (ETEC).
Enteroinvasive E. coli (EIEC).
Verocytotoxin-producing E. coli (VTEC)
What is Enterotoxigenic E. coli (ETEC)
Most important bacterial cause of diarrhea in children in developing countries.
- Most common cause of travellers’ diarrhea.
- It produces enterotoxins(heat stable-ST and heat labile-LT) which are similar to cholera toxins.
- Water contaminated by human or animal sewage may be important in spread
What is Enteroinvasive E. coli (EIEC)
Important cause of diarrhea in areas of poor hygiene.* Invasion of the intestinal mucosa, resulting in bloody diarrhoea.* Infections usually foodborne; no evidence of animal or environmental reservoir
What is Verotoxin-producing E. coli (VTEC)
Serotype 0157 most important EHEC in human infections.
- Causes two distinct conditions: haemorrhagic colitis due to the local action of the toxin on the gut or haemolytic uraemic syndrome in which the toxin causes haemolysis secondary to systemic microvascular angiopathy leading to renal failure.
- Food and unpasteurised milk important in spread
What is Enteropathogenic E. coli (EPEC)
EPEC strains belong to particular O serotypes.
* Cause direct damage to the intestinal wall and cause a diarrhoeal disease among infants, with bloody, mucous stools.
* Importance in adults not known
Pathogenesis of E. Coli
- The E coli strains associated with haemorrhagic colitis (i.e. VTEC), produce relatively large amounts of the bacteriophage-mediated Shiga-like toxin.
- Shiga toxin (Stxs) are a family of bacterial exotoxins responsible for bloody diarrheal disease that can progress to life-threatening systemic diseases, such as renal failure syndrome (HUS).
- The toxins activate innate immune cells, such as neutrophils or monocytes that act as “carrier” cells to deliver Stxs in the bloodstream and kidney.
- Toxins bind to GB3 receptors, globotriaosylceramide, which are present in renal tissue more than any other tissue
What is salmonella?
Salmonellae are the most common cause of food-associated diarrhea in many developed countries.
❖ All salmonellae except for S. typhi and S. paratyphi are found in animals as well as humans.
❖ Transmitted via contaminated food, especially poultry and dairy products.
❖ Can be transmitted from person to person.
❖ Salmonellosis ranges clinically from the common Salmonella gastroenteritis (diarrhea ,abdominal cramps & fever) to enteric fevers (including typhoid fever)
Pathogenesis of Enteric Fever - Typhoid
- Ingestion
- Pass through gastric acidity
- Small intestine (multiply)
- Mucosal penetration (minimal epithelial damage)
- Intestinal lymphatics
- Thoracic duct
- Bloodstream
- Spleen, liver, reticulo endothelial system
- Intracellular multiplication
- Reenter blood
- Re enter intestine through bile.
Complications of enteric fever - typhoid
Intestinal perforation and/or bleeding
● Hepatic or splenic abscesses
● Meningoencephalitis
● Nephritis, Arthritis or Osteomyelitis
Campylobacter
What is it?
Campylobacter species cause acute gastroenteritis with diarrhea, abdominal pain,fever, nausea, and vomiting.
❖ Poultry is the source of the majority of contamination.
❖ Pathogenesis and symptoms similar to salmonella.
❖ Incubation time and duration longer.
❖ The role of toxins in pathogenesis is unclear.
How is campylobacter classified?
The delay in recognising the pathogenesis of these organisms is due to theircultural requirements.
❖ Campylobacter pylori, now classified as Helicobacter pylori is an importantcause of gastritis and gastric ulcers.
❖ Campylobacter jejuni is also one of the most common species
What is Helicobacter pylori
The main cause of chronic gastritis. The infection usually remains in the stomach for decades. In a few patients, this may lead to ulcer and gastric carcinoma.
● H. pylori prevalence ranges between 85% and 95% in developing countries and between 30 and 50% in developed countries.
● How H. pylori is acquired and its route of transmission are unknown since humans are the only known reservoir of infection
Pathogenesis of Helicobacter
H. pylori pathogenesis is mediated by four steps:
● Survival in the acidic stomach
● Flagella-mediated motility colonisation of the gastric mucosa.
● Attachment to host cells by adhesins/receptors interaction.
● Tissue damage by toxin release including Cytotoxin-associated gene A (CagA), Vacuolating cytotoxin A (VacA).
What is Food-associated infection vs food poisoning:
Food-associated infection – food acts as a vehicle for the pathogen and provide conditions for multiplication.
● Food poisoning – consumption of food containing toxins.
● Toxins, may be chemical (e.g. heavy metals) or bacterial in origin.
● Bacteria multiply and produce toxins within contaminated food.
● Bacteria destroyed during cooking but toxins unaffected.
Food Poisoning
Common causes
● Enterotoxin of Staphylococcus aureus
● The heat-resistant spores of Bacillus cereus
● Spores of Clostridium botulinum cause infant botulism: rare but severe/Honey
● Listeria monocytogene
