PATHOGENESIS - Gastrointestinal Bacteria

Question 1

List the diseases that can be caused by Salmonella

Answer 1

Gastroenteritis
Systemic infection

Question 2

(T/F) Salmonella are not invasive pathogens

Answer 2

FALSE

Question 3

Describe the pathogenesis of Salmonella which cause gastroenteritis

Answer 3

Salmonella cross the gut mucosal surface and penetrate the lamina propria. For Salmonella which cause enteritis, there is a major influx of neutrophils and a marked inflammatory response. This destroys the architecture of the gut wall and causes diarrhoea

Question 4

Describe the pathogenesis of Salmonella which cause systemic infection

Answer 4

Salmonella cross the gut mucosal surface and penetrate the lamina propria. For Salmonella which cause systemic infection, there is a major influx of macrophages. These Salmonella can infiltrate the macrophages and be transported to the lymph nodes, through the lymph, and into the bloodstream - causing septicaemia

Question 5

Why does Salmonella promote the host inflammatory response?

Answer 5

Salmonella promotes inflammation in order to combat the host normal gut flora which is resistant to the infection

Question 6

What are type III secretion systems (molecular syringes)?

Answer 6

Type III secretion systems are multi molecular structures with the ability to penetrate a cell, allowing bacteria to translocate effector proteins from the bacterial cytoplasm into the host cell. These effector proteins interfere with the host cell cytoskeleton leading to the host cell taking in the bacteria (also known as membrane ruffling)

Question 7

(T/F) Type III secretion systems are often a virulence factor associated with Gram negative bacteria

Answer 7

TRUE

Question 8

What does the Salmonella pathogenicity island 1 (SP1) encode for?

Answer 8

SP1 encodes for a type III secretion system which allows the bacteria to invade gut epithelial cells

Question 9

What does the Salmonella pathogenicity island 2 (SP2) encode for?

Answer 9

SP2 encodes for a type III secretion system which is essential for the bacteria to live and replicate within macrophages

Question 10

What is pathotyping?

Answer 10

Pathotyping is the categorising of groups of organisms within the same species that have the same pathogenicity for a specific host

Question 11

List the three virulence factors of Entertoxigenic E. coli (ETEC)

Answer 11

Heat labile enterotoxin (LT)
Heat stable enterotoxin (ST)
Fimbriae

Question 12

Describe the pathogenesis of ETEC

Answer 12

The fimbriae attach to the enterocytes of the gut and the ETEC inject enterotoxin causing a disruption in the electrolyte balance in the cell. As a consequence, the water balance in the gut is imbalanced causing non-inflammatory, watery diarrhoea

Question 13

List the virulence factors of Enteropathogenic E. coli (EPEC)

Answer 13

Pathogenicity island which encodes for a type III secretion system, intimin and particular fimbriae

Question 14

What are the two diseases caused by Enterohemorrhagic E.coli (EHEC) infection?

Answer 14

Haemorrhagic colitis
Haemolytic uraemic syndrome (HUS)

Question 15

List the virulence factors of Enterohaemorrhagic E. coli (EHEC)

Answer 15

• Pathogenicity island which encodes for a type III secretion system, intimin and fimbriae
• Shiga toxin

Question 16

What is the most virulent serotype of EHEC?

Answer 16

E. coli 0157:H7

Question 17

What encodes for the shiga toxin produced by EHEC?

Answer 17

Lysogenic bacteriophages encode for the shiga toxin

Question 18

Describe the pathogenesis of EHEC

Answer 18

EHEC produce shiga toxin which crosses the intestinal epithelial cells and is spread systemically through the bloodstream, binding to and invading endothelial cells. The shiga toxin is transported in a vesicle to the endoplasmic reticulum, causing a disruption in protein synthesis and killing the host cell. The damage to the endothelial cells triggers the coagulation cascade leading to the formation of microthrombi, causing distal ischaemic necrosis, platelet consumption and erythrocyte fragmentation

Question 19

What are the clinical signs of haemorragic colitis?

Answer 19

• Sudden onset of severe cramps and abdominal pain
• Bloody diarrhoea
• Nausea and vomiting
• Pyrexia

Question 20

What are the clinical signs of haemolytic uraemic syndrome (HUS)?

Answer 20

• Haemolytic anaemia
• Thrombocytopenia
• Renal failure

Question 21

Why does giving antibiotics to patients with haemolytic uraemic syndrome (HUS) often make the condition worse?

Answer 21

Antibiotics cause the lysogenic bacteriophages which are encoding for the shiga toxin to go into the lytic cycle, leading to the replication of more phage particles as well as lysis of the bacterial cell - causing the production and release of even more shiga toxin