MI: GI infections Pt.2 Flashcards
What type of bacteria are Salmonellae?
- Gram-negatives, Non-lactose fermenting,
- Produce hydrogen suphide (form black colonies)
- Grows on TSI agar, XLD agar and selenite F broth
Which antigens are found on Salmonellae?
- LPS O antigen (groups A-I)
- Flagellar H antigen
- Capular Vi antigen (virulence, antiphagocytic)
NOTE: differences in these antigens help identify the serotypes of Salmonellae
List 2 main species of Salmonella.
- Salmonella typhi
- Salmonella enterica
What are 2 important serotypes of S. enterica?
- Salmonella enterica serotype Enteritidis
- Salmonella enterica serotype Typhimurium
How is Salmonella Enteritidis transmitted?
Via infected poultry, eggs, meat
Describe the presentation of Salmonella Enteritidis.
Causes enterocolitis - self-limiting diarrhoea that is non-bloody
- Bacteraemia is rare
- Usually no treatment required
How is Salmonella typhi transmitted?
- Transmitted only by humans (faeco-oral)
- Multiplies in Peyer’s patches and spreads via the endoreticular system
Describe the presentation of Salmonella typhi.
Causes typhoid fever with constipation
(rose coloured spots)
Which subset of patients are at increased risk of Salmonella bacteraemia?
Sickle cell patients
How is Salmonella typhi treated?
Ceftriaxone
What are some key microbiological features of Shigella?
(stains etc)
- Gram negative
- Non-lactose fermenter
- Does NOT produce hydrogen suphide
- Non-motile
Which antigens are seen on Shigella?
LPS O antigens
Polysaccharide (groups A-D) used to identify species
List some types of Shigella.
- Shigella sonnei
- Shigella dysenteriae
- Shigella flexneri (MSM)
What is the most effective bacterial enteric pathogen and why?
Shigella - it has the lowest infective dose (50)
NOTE: Shigella has no animal reservoir and no carriers state
How does Shigella infection manifest? How do you treat it?
Dysentry
- Severe diarrhoea with blood and mucus in the faeces
- Invades the cells of the distal ileum and colon
- Produces shiga toxin
Avoid antibiotics when treating, however use ciprofloxacin if required
What are the microbiological features of Vibrio Cholerae?
- Gram-negative
- Comma-shaped
- Late lactose-fermenters
- Oxidase-positive
What are the different groups of Vibrio cholerae?
- O1 - causes epidemics
- Non-O1 - sporadic, non-pathogens
How is Vibrio cholerae transmitted?
Contamination of water and food from human faeces
What type of GI disturbance does Vibrio cholerae cause and how do you treat it?
- Produces massive watery (secretory) diarrhoea without inflammatory cells
- Treat by replacing the water and electrolytes lost
Name and describe the key features of other types of Vibrio.
How is it treated?
Vibrio parahaemolyticus:
- Caused by ingestion of raw/undercooked seafood
- Causes self-limiting diarrhoea (3 days)
- Grows on salty agar
Vibrio vulnificus:
- Causes cellulitis in shellfish handlers
- Can cause fatal septicaemia with diarrhoea and vomiting in HIV patients
Treat both with doxycycline
