Changes

*Member of ''Enterobacteriacae'' family of Gram-negative bacilli

*Member of ''Enterobacteriacae'' family of Gram-negative bacilli

*Facultative anaerobe

*'''Facultative anaerobe'''

*One of predominant bacterial species in colonic flora

*One of predominant bacterial species in colonic flora

*Colonisation of intestinal tract from environmental sources shortly after birth

*Colonisation of intestinal tract from environmental sources shortly after birth

*Usually motile with flagella and fimbriae

*Usually motile with flagella and fimbriae

*Oxidase negative (do not possess cytochrome C oxidase)

*'''Oxidase negative''' (do not possess cytochrome C oxidase)

*Grow on MacConkey agar (in presence of bile salts), producing pink colonies

*Grow on '''MacConkey agar''' (in presence of bile salts), producing pink colonies

*Haemolytic activity on blood agar characteristic of certain strains

*'''Haemolytic activity'' on blood agar characteristic of certain strains

*Lactose fermenter

*'''Lactose fermenter'''

*Reduce nitrates to nitrites and ferment glucose to produce acid and gas

*Reduce nitrates to nitrites and ferment glucose to produce acid and gas

*Possess a lipopolysaccharide (O) antigen, a flagellate (H) antigen, polysaccharide capsule (K) antigens and fimbrial (F) antigens

*Possess a lipopolysaccharide ('''O''') antigen, a flagellate ('''H''') antigen, polysaccharide capsule ('''K''') antigens and fimbrial ('''F''') antigens

*Epidemiological typing of ''E. coli'' uses antigen combinations, eg. O125:K12:H42

*Epidemiological typing of ''E. coli'' uses antigen combinations, eg. O125:K12:H42

===Pathogenesis===

===Pathogenesis===

*Virulence factors include capsules, endotoxin, enterotoxins and colonisation factors

*<u>Virulence factors</u> include capsules, endotoxin, enterotoxins and colonisation factors

*Capsular polysaccharides produced by some strains prevent phagocytosis and interfere with complement

*Capsular polysaccharides produced by some strains prevent phagocytosis and interfere with complement

*Endotoxin is a lipolysaccharide component of the cell wall of Gram-negative bacteria, composed of lipid A, a core polysaccharide and various side chains

*Endotoxin is a lipolysaccharide component of the cell wall of Gram-negative bacteria, composed of lipid A, a core polysaccharide and various side chains

*Endotoxin is realeased when bacteria die, and causes endothelial damage leading to disseminated intravascular coagulation and endotoxic shock; it is also a pyrogen

*'''Endotoxin''' is realeased when bacteria die, and causes endothelial damage leading to '''disseminated intravascular coagulation''' and e'''ndotoxic shock'''; it is also a '''pyrogen'''

*Enterotoxins, verotoxins and cytotoxic necrotising factors produced by many pathogenic ''E. coli''; these produce cell damage at their site of action

*Enterotoxins, verotoxins and cytotoxic necrotising factors produced by many pathogenic ''E. coli''; these produce cell damage at their site of action

*Alpha-haemolysin may increase iron availability for invading organisms

*'''Alpha-haemolysin''' may increase iron availability for invading organisms

*Siderophores are made by certain pathogenic strains, and are responsible for iron aquisition; they include aerobactin and enterobactin

*'''Siderophores''' are made by certain pathogenic strains, and are responsible for iron aquisition; they include aerobactin and enterobactin