Escherichia Coli

Question 1

Describe E.coli

Answer 1

• Gram negative bacteria
• Bacili (rods)
• Lactose fermenting
• Facultatively anaerobic
• Part of the large bowel microbiota

Question 2

What type of agar is used to detect E.coli and explain why it is used specifically

Answer 2

MacConkey agar

-has lactose and pH indicator (usually yellow but turns red)

Question 3

What are serological antigens of E.coli? (4)

Answer 3

K - capsule
O - LPS
F - fimbriae
H - flagella

Question 4

List a few conditions E.coli can cause

Answer 4

• Intestinal infections (diarrhoea)
• Toxin-mediated disease
• Extra-intestinal infections e.g. UTI, neonatal meningitis, blood stream infections

Question 5

What are the 6 pathotypes of E.coli causing diarrhoea?

Answer 5

• Enterotoxigenic E.Coli (ETEC)
• Enteropathogenic E.Coli (EPEC)
• Enteroaggregative E.Coli (EAEC)
• Enteroinvassice E.Coli (EIEC)
• Diffusely adherent E.Coli (DAEC)
• Shiga toxin-producing E.Coli (STEC)/ Enterohemorrhagic (EHEC)

Question 6

Which pathotype of E.Coli is the leading cause of traveler’s diarrhoea?

Answer 6

ETEC

Question 7

Describe the virulence factor of ETEC

Answer 7

Produce heat stable toxins and heat labile toxins

-stimulate lining of the intestine to secrete excessive fluid

Question 8

Which pathotype of E.Coli is the leading cause of diarrhoea in paediatrics?

Answer 8

EPEC (and EIEC)

Question 9

Describe how EPEC cause diarrhoea

Answer 9

Type 3 mediated secretion of bacterial proteins

• insertion of translocated intimin receptor
• EPEC produces intimin thus can bind
• other proteins causes a reorganisation in actin cytoskeleton forming a pedestal
• loss of microvilli

Question 10

Describe how STEC/EHEC cause haemorrhagic colitis (bloody diarrhoea)

Answer 10

1) Shiga toxin has alpha and beta subunits
2) B subunit binds to host cell = endocytosed
3) Transported to golgi and ER
4) On the way, A subunit is cleaved to A1 and A2
5) A1 inactivates ribosomes = inhibit protein synthesis = cell death

Question 11

What are extra-intestinal pathogenic E.Coli (ExPEC)?

Answer 11

Strais of E.Coli capable of causing disease outside intestinal tract

Question 12

What type of E.Coli causes UTI?

Answer 12

Uropathogenic E.Coli (UPEC)

Question 13

What are the two types of UTI?

Answer 13

Cystitis (lower UTI)

Pyelonephritis (upper UTI)

Question 14

What are the virulence factors of UPEC?

Answer 14

• Adhesins = helps invasion
• Toxins e.g. poreforming toxins
• Iron acquisition = produce their own iron-complexing proteins
• Immune invasion

Question 15

How is diarrhoea treated?

Answer 15

Oral rehydration (clear liquids)

Question 16

Antibiotics for UTI?

Answer 16

Trimethoprim or nitrofurantoin (cystitis)

Co-amoxiclav (pyelonephritis)

Question 17

Antibiotics for bloodstream infections?

Answer 17

Co-amoxiclav