Infection 19 - E.Coli

Question 1

Describe the structure + properties of E.coli

What kind of infections can E.coli cause?

Answer 1

• Gram-negative bacilli, facultatively anaerobic, lactose-fermenting (goes red on MacConkey agar)
• Commensal in large bowel, protects us against salmonella
• UTI’s, intestinal tract infections, biliary tract infections, neonatal meningitis or sepsis (most common bloodstream infection)

Question 2

How are E.coli strains classified?

Answer 2

1) Serology - using surface antigens O (LPS), H (flagella), K (capsule) + F (fimbriae)
2) Genetic diversity - e.g.: whole genome sequencing or DNA hybridisation.

Question 3

What are the 6 strains of diarrhoaegenic E.coli?

Which 2 are common in children in the developing world?

Answer 3

1) Enterotoxigenic E.coli (ETEC)
2) Enteropathogenic E.coli (EPEC)
3) Enteroaggregative E.coli (EAEC)
4) Enterinvasive E.coli (EIEC)
5) Diffusively adherent E.coli (DAEC)
6) Shiga toxin-producing E.coli (STEC) - AKA VTEC or EHEC, which cause extra-intestinal disease

• EPEC + EIEC

Question 4

How can E.coli infections be prevented?

Answer 4

• Avoid food + water contaminated with bacteria

- E.g.: raw fruit + veg, uncooked meat + untreated water

Question 5

How do you treat E.coli?

Answer 5

• Clear liquids to replace electrolytes/prevent dehydration
• Avoid antibiotics unless UTI related
• Trimethoprim + nitrofurantoin for UTI related E.coli infections

Question 6

What is enterotoxigenic E.coli (ETEC) also known as?
What toxins produce the symptoms?
How do you treat?

Answer 6

• Travellers diarrhoea
• Heat stabile toxin + Heat labile toxin - stimulate linings of intestines to secrete extra fluid producing watery diarrhoea and abdominal cramping
• Lasts 3-4 days, don’t give AB’s as causes bacteria to produce more toxin.

Question 7

How does enteropathogenic E.coli (EPEC) cause diarrhoea?

Answer 7

• Type lll secretion machinery secretes TIR (translocated intimin receptors) into the enterocyte
• TIR attaches to cell membrane and acts as a receptor for intimin so bacterial cells can now attach.

Question 8

What are the symptoms of shiga toxin producing E.coli (STEC)?
How does it cause these symptoms?

Answer 8

• Haemolytic Uraemic Syndrome (HUS) - a triad of haemolytic anaemic, acute renal failure and thrombocytopenia
• Watery diarrhoea followed by bloody diarrhoea, but little to no fever
• Toxin binds to Gb3 on host cell surface, endocytosed and transported to endoplasmic reticulum. A1 part of toxin inactivates ribosomes, stopping PS and causing cell death.

Question 9

What does uropathogenic E.coli (UPEC) cause?

What its its virulence factors?

Answer 9

• UTI’s, or cystitis if migrating to the bladder (inflammation of the bladder) or pyelonephritis if migrating further to the kidney (kidney inflammation)
• Type 1 fimbriae have adhesive tips that bind to uroepithelium and cause invasion, LPS toxin + iron acquisition via siderophores