Escherichia coli

Question 1

E.coli

Morphology

Answer 1

Gr- rods, non-sporeforming
O, K, H AGs & pili

Question 2

E. coli

Antigenic structure

Answer 2

LPS: O & Lipid A, K-capsule, H-flagella, pili

Question 3

E. coli

Diagnostic characteristics

Answer 3

Motile, Glu & lac fermenters, Nitrate reducer, catalase + and oxidase -

Question 4

E. coli

Media

Answer 4

Selective media:
MacConkey & levine –> Klgiler’s iron agar & motlity test

Question 5

UPEC - factors

Answer 5

Uropathogenic
- pili (adhesion)
- adhesins (adhesion)
- hemolysins (invasion)
- (K - for pyelonephritis causing strains) (evasion)

Question 6

EPEC - factors

Answer 6

Enteropathogenic
- T3 secreting system (intimin receptor insertion –> expressed on host –> bind intimin = strong adhesion)
- actin polymerization –> loss of microvilli –> lost absorption

Question 7

EPEC - demographic/symptoms

Answer 7

1. infants (devloping countries)
2. watery non-bloody diarrhea (occasional vomiting & fever)

Question 8

ETEC - factors

Answer 8

Enterotoxigenic
- Exotoxins
- colonization factors
* heat-labile (LT): B - bind enterocyte & A - activate –> cAMP –> intense hypersecretion H2O & Cl- + no Na+ reabsorption.
* heat-stable (ST): –> cGMP –> fluid secretion + no absorption

Question 9

ETEC - demographic/symptoms

Answer 9

1. Traveler’s & <5y/o children (developing countries)
2. watery non-bloody diarrhea (occasional vomiting & nausea)

Question 10

STEC - factors

Answer 10

• shiga-like toxin 1 (Stx-1): like Shigella dysenteriae type1
• shiga-like toxin 2 (Stx-2): bind Gb3 on host’s intestinal villi or renal endothelium –> A: ribosomal RNA –> no protein synthesis
  ==> hemolytic uremic syndrome

Question 11

STEC

Hemolytic uremic syndrome

Answer 11

• mostly in <10y/o children
  Stx2 –> renal endothelial cells –> no protein synthesis –> destroyes cell –> platelet activation –> thrombin activation –> microthrombi formation –> low renal filtration –> acute renal failure
  Increased: creatinine & urea in peripheral blood
  Decreased: GFR
  Thrombocytopenia & microangiopathic hemolytic anemia
• Decreased RBCs & Hgb in peripheral blood

Question 12

STEC - source/symptoms

Answer 12

1. undercooked ground beef, meat products, unpasteurized milk & juices
2. severe & bloody diarrhea, associated hemorrhagic colitis + hemolytic uremic syndrome

Question 13

EIEC - demographic/symptoms

Answer 13

Enteroinvasive - invades intestinal mucosa cells
1. travelers & children (developing countries)
2. watery diarrhea –> dysenteric form (more severe: fever + abdominal cramps + blood & leukocytes in feces)

Question 14

EAEC - factors

Answer 14

Enteroaggregative
- adhesion factors
- toxins (ex. shiga-like)
- hemolysin (invasion)

Question 15

EAEC - Characteristic/symptoms

Answer 15

1. autoagglutination/aggregation over epithelium in small intestine
2. chronic diarrhea & growth retardation (children), also acute diarrhea + fever, nausea, vomiting & abdominal pain

Question 16

Other E. coli caused complications

Answer 16

1. meningitis (mostly with K AG)
2. sepsis (newborns, lacking IgM ABs or secondary to UTIs/abdominal infections in elderly)
3. pneumonia, wound infections, endocarditis & catheter infections

Question 17

E. coli

immunity

Answer 17

ABs do not protect against recurrent infections

Question 18

E. coli

Prophylaxis (transmission)

Answer 18

Non-specific (fecal-oral transmission)

Question 19

E. coli

Therapy

Answer 19

Symptomatic (fluids, electrolytes etc)
Antibiotics (based on susceptability, UPEC can be resistant)