MI: GI infections Pt.2

Question 1

What type of bacteria are Salmonellae?

Answer 1

• Gram-negatives, Non-lactose fermenting,
• Produce hydrogen suphide (form black colonies)
• Grows on TSI agar, XLD agar and selenite F broth

Question 2

Which antigens are found on Salmonellae?

Answer 2

• 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

Question 3

List 2 main species of Salmonella.

Answer 3

• Salmonella typhi
• Salmonella enterica

Question 4

What are 2 important serotypes of S. enterica?

Answer 4

• Salmonella enterica serotype Enteritidis
• Salmonella enterica serotype Typhimurium

Question 5

How is Salmonella Enteritidis transmitted?

Answer 5

Via infected poultry, eggs, meat

Question 6

Describe the presentation of Salmonella Enteritidis.

Answer 6

Causes enterocolitis - self-limiting diarrhoea that is non-bloody

• Bacteraemia is rare
• Usually no treatment required

Question 7

How is Salmonella typhi transmitted?

Answer 7

• Transmitted only by humans (faeco-oral)
• Multiplies in Peyer’s patches and spreads via the endoreticular system

Question 8

Describe the presentation of Salmonella typhi.

Answer 8

Causes typhoid fever with constipation
(rose coloured spots)

Question 9

Which subset of patients are at increased risk of Salmonella bacteraemia?

Answer 9

Sickle cell patients

Question 10

How is Salmonella typhi treated?

Answer 10

Ceftriaxone

Question 11

What are some key microbiological features of Shigella?
(stains etc)

Answer 11

• Gram negative
• Non-lactose fermenter
• Does NOT produce hydrogen suphide
• Non-motile

Question 12

Which antigens are seen on Shigella?

Answer 12

LPS O antigens

Polysaccharide (groups A-D) used to identify species

Question 13

List some types of Shigella.

Answer 13

• Shigella sonnei
• Shigella dysenteriae
• Shigella flexneri (MSM)

Question 14

What is the most effective bacterial enteric pathogen and why?

Answer 14

Shigella - it has the lowest infective dose (50)

NOTE: Shigella has no animal reservoir and no carriers state

Question 15

How does Shigella infection manifest? How do you treat it?

Answer 15

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

Question 16

What are the microbiological features of Vibrio Cholerae?

Answer 16

• Gram-negative
• Comma-shaped
• Late lactose-fermenters
• Oxidase-positive

Question 17

What are the different groups of Vibrio cholerae?

Answer 17

• O1 - causes epidemics
• Non-O1 - sporadic, non-pathogens

Question 18

How is Vibrio cholerae transmitted?

Answer 18

Contamination of water and food from human faeces

Question 19

What type of GI disturbance does Vibrio cholerae cause and how do you treat it?

Answer 19

• Produces massive watery (secretory) diarrhoea without inflammatory cells
• Treat by replacing the water and electrolytes lost

Question 20

Name and describe the key features of other types of Vibrio.
How is it treated?

Answer 20

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