PRAC: Gastroenteritis

Question 1

What are some outcomes of infections of the gastrointestinal tract?

Answer 1

Local:

• asymptomatic (Most)
• mild, self-limiting diarrhoea +/- vommiting
• life threatening loss of fluid

Question 2

What is the pathogenesis of infections of the GIT?

Answer 2

Pathogenesis is associated with the symptoms

• ingestion of the pathogen –> replication –> toxin production
• inflammatory response
• invasion

OR

Ingestion of the pre-formed toxin (ie. Bacillus cereus/ Staphylococcus aureus) –> vomiting (4-6 hours)

Question 3

What is the significance of the incubation period of infectious agents of the GIT?

Answer 3

• used to identify infectious agent as different aetiological microbes have differing incubation periods.
• difference between ingestion/infection and symptoms

Question 4

What is the significance of the infectious dose in GIT infections?

Answer 4

• It is the number of organisms that need to multiply to critical number to cause disease.
• it has serious implications for food handling as the number of bacteria/microbes can influence food poisoning.
• also depends upon the host environment
• -> cheese, chocolate etc. protect organisms
• -> antacids can decrease the acid in the stomach and decrease infectious dose

Question 5

What are some public health aspects of food-borne gastroenteritis?

Answer 5

• most gastroenteritis is transmitted via contaminated food or water, but can be person-to-person spread (ie. shigella) or from animal to human (zooonosis - EHEC)
• -> petting zoos are particularly bad for this
• food-associated diarrhoea is a public health issue and should always be investigated
• -> workers, food handling processes, food in question etc.

Question 6

What are some Lab investigations for the diagnosis of GIT infections

Answer 6

Investigate when the patient is seriously ill, has bloody diarrhoea, is hospitalised, is associated with a supended outbreak of gastro or is a returned traveller.

Faeces microscopy:

• -> gross appearance
• -> look for leucocytes +/- red blood cells
• -> cysts, trophozoites, eggs (ova) or even worms (parasites)

Faeces Culture:

• -> collect specimen from site of infection
• -> intermittent excretion (take three consecutive samples make need duodenal sampling for certain parasites–> done with a capsule and string that is partly swallowed and then brought back up)
• -> used on selective media as well as enrichment media

Question 7

What specific media is used to identify Salmonella?

Answer 7

Selenite Broth (Enrichment Media)
--> may create a brick red precipitate

Question 8

What does DCA select for?

Answer 8

• -> more selective than MAC and wipes out even E.Coli.
• -> It identifies Salmonella and Shigella
• -> pale pink or yellow colonies as they are lactose non-fermenters
• -> also allows us to identify if they make H2S gas (black dot)
• -> black centre is not shigella; may be salmonella

Question 9

What does MAC select for?

Answer 9

• -> lactose fermenters = pink
• -> Lactose nonfermenters = pale pink or yellow
• -> E.coli, salmonella, shigella etc.
• -> If E.Coli is suspected, then virulence tests are conducted

Question 10

What does CAMP select for?

Answer 10

• -> only Campylobacter Jejuni.
• -> it needs microaerophilic conditions (decreased O2 saturation; grown at 42 degrees–> because they are adapted to grow in the gut of chickens)

Question 11

What are some other tests to identify GIT infections?

Answer 11

• Other tests to detect virulence determinants
• -> ie/ PCR for specific genes of pathogenic bacteria (EHEC)
• Analysis of serum samples for antigens or antibodies
• -> ie/ investigation of infectious hepatitis