Escherichia coli

Question 1

Common characteristics of E.coli, Klebsiella, Proteus (9)

Answer 1

Normal flora of intestinal tract (colon)
Enterobacteriacae
Grow on simple media, including enteric medium —> MacConkey agar
Gram-negative bacilli, Non-spore formers
Ferment glucose with or without gas production
Motile or Non-motile
Aerobe and Facultative anaerobe
Reduce nitrate to nitrite

Possess Somatic (O) antigen, Flagellar (H) antigen, Fimbrial (P, F, CS) antigens, or Capsular (K) antigens

Question 2

General Characteristics (5)

Answer 2

MOST ABUNDANT AEROBIC flora of COLON

Used as INDICATOR of FAECAL POLLUTION of water and food

Gram-negative, MOTILE bacilli

Grow on MACONKEY agar, producing NON-MUCOID, PINK colonies (due to LACTOSE-FERMENTATION)

FERMENT SUGAR producing ACID and GAS

Question 3

Antigens (4)

Answer 3

LPS (O) antigen

Flagellar (H) antigen

Capsular (K) antigen

Fimbrial antigens

Question 4

Diseases (2)

Answer 4

1- Intestinal (Diarrhea)

2- Extra-intestinal (UTI, Neonatal meningitis, Septic shock)

Question 5

Virulence Factors (3)

Answer 5

1- NEONATAL infection —> Capsular (K1, K5) antigens

2- UTI —> Type 1 and P fimbriae

3- EXTRA-INTESTINAL infections —> Hemolysin, Cytotoxin, Siderphores (iron-chelating)

Question 6

Pathotypes of Diarrheogenic E.coli (5)

Answer 6

Enterotoxigenic 
Enteroinvasive 
Enteropathogenic
Enterohaemorrhagic 
Enteroaggregative

Question 7

Enterotoxigenic E.coli (4)

Answer 7

Watery, cholera-like diarrhea

In children in developing countries

Traveller’s diarrhea

Heat-labile Enterotoxin —> Elevates cAMP
Heat-stable Enterotoxin —> Elevates cGMP

Question 8

Enteroinvasive E.coli (4)

Answer 8

Bacillary dysentery (stool with mucus, blood, pus)

All ages, more common in less developed countries

INVADING COLONIC MUCOSA

Closely related to Shigella

Question 9

Enteropathogenic E.coli (3)

Answer 9

Non-specific Gastroenteritis

Children up to 2 years in less developed countries

ATTACH to and DESTROY SMALL INTESTINAL EPITHELIAL CELLS (attaching and effacing lesion)

Question 10

Enterohaemorragic E.coli (8)

Answer 10

Bloody diarrhea and HUS
Children and elderly in INDUSTRIALIZED countries
Other names: Verocytotoxin-producing E.coli (VTEC) and Shiga toxin-producing E.coli (STEC)
Disease mediated by SHIGA TOXINS
Predominant serotype O157:H7
Reservoir of infection —> INTESTINAL TRACT of CATTLE and OTHER ANIMALS
Transmitted MAINLY through CONTAMINATED MEAT (under-cooked ground beef hamburger meat) —> “Hamburger E.coli”
Transmission also by CONTAMINATED SALADS and UNPASTEURIZED FRUIT JUICES (contamination by animal faeces or animal-faeces derived manure in field)

Question 11

Enteroaggregative E.coli (3)

Answer 11

PERSISTENT (>14 days) diarrhea and ACUTE diarrhea

Children in less developed countries, travellers, HIV/AIDS patients

ADHERENCE of BACTERIAL AGGREGATES to COLONIC MUCOSA