L3-4. Infectious Causes of Gastroenteritis Flashcards
Why are children more susceptible to the effects of diarrhoea? What are the consequences of this?
They have smaller blood volumes and thus are more susceptible to changes and imbalances of electrolytes and fluids. The major problem is malabsorption and nutrient deficiencies caused by diarrhoea (including dehydration) which leads to higher susceptibility to infection.
What is the normal course of diarrhoea?
It is usually self-limited and most often presents as an acute disease that resolves in less than three weeks. The danger is the dehydration and electrolyte imbalances that ensue in diarrhoea
What is the difference between infection and intoxication in terms of diarrhoea? Give two examples of each.
Bacterial infection refers to ingestion of the pathogen in contaminated food or water leading to replication and colonisation in the gut and subsequent pathology.Eg. Salmonella and E.coliBacterial intoxication is the ingestion of bacterial toxins that contaminate the food or water leading to pathology. Eg. Staphylcoccus and Bacillus cereus
Describe the association between diarrhoea and malnutrition
This occurs in two major cateDescgorical causes:1. Increased loss of Energy: diarrhoea and vomiting and increased metabolic requirements2. Reduced intake of Energy: anorexia and malabsorption
Describe the flow of water through the gastrointestinal system in any one day
About 2 L is ingested in the food per day The body secretes approximately 8L worth of fluid into the gut tube per day through saliva, mucosal secretions, enzymes and acid secretions. At the same time water is being reabsorbed by the gastrointestinal tract. Most of it (5.5L) is absorbed in the small intestine, about 3L in the ileum and about 1.4L in the colon. 10 L into the lumen and 9.9L being reabsorbed.Thus humans defecate only about 100mL of fluid per day in the faeces
What are the four major mechanisms of diarrhoea?
- Secretory (caused by infection)2. Osmotic (caused by decreased production and content of plasma proteins)3. Motility (usually caused by drugs and alcohol)4. Exudative (due to mucosal damages such as Chron’s)
Describe the difference between small bowel and large bowel diarrhoea
Small BowelBecause the majority of water absorption occurs in the small intestine, the diarrhoea involved in small bowel pathology is often more profuse and watery. Fluid entering the bowel»_space; capacity to absorb itThus frequent, high volume, watery stoolsLarge BowelBy the time the stool reaches the large intestine, most water is already reabsorbed. Hence diarrhoea from the large intestinal pathology tends to be less fluid and smaller in volume. The stools tend to contain pus or blood
What is the difference between the causative organisms of diarrhoea between developing and developed countries?
Developing countries: bacterialDeveloped countries: viralthis is only a trend
What is non-specific gastro?What is the cause?Who is most affected?
A general inflammation of the small and large bowelsCaused by variety of bacteria, viruses and protozoaChildren are most affected with this
What is dysentry?Is it only caused by infection?What are the major causative organisms?
Dysentry is the presence of blood, pus and mucous in the diarrhoeaIt is usually caused by gastrointestinal infection but can also be a symptom of oestocolitis, cancer and othersThe major causative organisms are Enteroinvasive E.coli (EIEC) or Shigella and Protozoa including Entamoeba Histolytic and Tryptosporidia spp.
Foodborne diarrhoea is often associated with outbreaks. What are some causes of foodborne diarrhoea and give some features of each cause.
Enterohaemorrhagic E.coli (EHEC) - only a very low dose is required for infectionSalmonella: infects the gut epithelium and colonises leading to inflammation mediated damage and malabsorptionCampylobacter - present in birds (uncooked chicken)Bacilus cereus: toxin producing and found in rice, wheat, potatoesViral: Norvirus (very infectious) and Rotavirus (mainly children)Clostriduium perfringens: ingestion of spores which sporolate in the gut and release toxinsStaph Vibrio cholarea Ciguatoxin is a non-infectious form of intoxication found in fishSSCCC EBVV
Why do many people suffer from Traveller’s Diarrhoea?What are some major causes of it?
Because travelling to different global locations exposes people to microbes that they have never seen before: first exposure response. causes include Enterotoxigenic E.coli (ETEC) and other various viruses and protozoa
What is the major cause of psuedomembranous colitis?What organisms causes this? What is the pathogenesis?In what setting is this most commonly seen?
Pseudomembranous colitis is due to Antibiotic associated Diarrhoea. Antibiotics destroy commensal organisms leaving the resistant Clostridium difficile to colonise (opportunistic) and cause damagePseudomembranous colitis can also sometimes occur due to direct toxicity of the antimicrobial itselfIt is most commonly seen in hospital settings and is difficult to control as they are very resistant bacteria
What is haemorrhagic colitis? How is it different to dysentry?What is the major organism that causes haemorrhagic colitis? And how?
It is diarrhoea that has blood in itIt is different as it doesn’t have pus and mucous like dysentryEnterohaemorrhagic E.coli (EHEC) which produces Shiga like toxins. Shigella dysenterii also causes this (not any other Shigella).
What are the causes of cholera-like diarrhoea?
VibriocholeraEnterotoxigenic E.coli (ETEC)Production of very watery diarrhoea
What are the causes of Enteric fever diarrhoea?
This is only a component of the Enteric Fever (not the main pathology)- Salmonella Typhi and paratyphi ie. Thyphoid fever
What are the different types of E.coli?Give a small description of each and what kind of diarrhoea they produce
- Enterotoxigenic (ETEC): don’t invade but cause toxins that are heat labile and heat stable and produce toxins - traveller’s diarrhoea and cholera like diarrhoea. = WATERY2. Enteropathogenic (EPEC): adhere to the intestinal wall, without invasion and cause brush border damage disease = NON-SPECIFIC GASTRO3. Enteroinvasive (EIEC): adhere to and invade into the intestinal wall = DYSENTRY4. Enterohaemorrhagic (EHEC): adhere to and cause damage to the intestinal walls = BLOODY DIARRHOEA5. Enteroaggregative (EAEC): WATER DIARRHOEA
What two types of E.coli express the adhesion molecule intimin?
EPEC and EHEC
What are the three major types of invasion of the gut lining? Give an example of each type
- Invasion that is limited to the mucosa (move from cell to cell rather than deeper in): Shigella2. Invasion limited to the submucosa: Salmonella and Campylobacter3. Invasion systemically: Salmonella
Describe the two stage model of EPEC adherence:
- Initial sticking in close proximity to the epithelial lining (plasmid mediated)2. Chromosomally encoded release of toxins to adhere more tightly (form effacement for attachment)
Describe the adhesion process of EPEC in terms of its pathogenicity
Type 3 secretion (t3S) is used by the EPEC bacteria to insert toxins directly into the host epithelial cell to cause damage. This damage enables the EPEC to insert (along with the toxins) a receptor TirThis receptor is expressed on the host cell and it binds to Intimin on the EPEC outer membrane. This interaction enables adhesion of the bacteria
How is this adhesion process of Tir and Intimin encoded?
On a pathogenicity islandThis means that there is a collection of genes that play a role in virulence and that are NOT present in the non-pathogenic strains of the same species.
Is it easier for bacteria to colonise the small or large intestine?
Easier to colonise the large intestine because there is much less motility; a lower strength adhesion is required.
What are four major virulence determinants of gastrointestinal bacterium?
Adhesins (by fibriae or non-fibriated means)Invasive abilityExotoxins: cytotonic or cytotoxicAbility to resist killing by the host immune system
