Changes

*Enterotoxigenic ''E. coli'' (ETEC):

*Enterotoxigenic ''E. coli'' (ETEC):

**General:

**General:

** Contributes to [[Intestines - Catarrhal Enteritis#Undifferentiated Neonatal Calf Diarrhoea|undifferentiated neonatal calf diarrhoea]], a mixed viral enteritis in calves, also known as enteric colibacillosis

*** Contributes to [[Intestines - Catarrhal Enteritis#Undifferentiated Neonatal Calf Diarrhoea|undifferentiated neonatal calf diarrhoea]], a mixed viral enteritis in calves, also known as enteric colibacillosis

**Causes scours in pigs, calves and lambs

***Causes scours in pigs, calves and lambs

**'Traveller's diarrhoea' in humans

***'Traveller's diarrhoea' in humans

**Pathogenesis:

**Pathogenesis:

**Oral infection, intestinal colonisation and toxin production

***Oral infection, intestinal colonisation and toxin production

**Fimbrial antigen or colonisation factor antigens (CFAs)determine species specificity

***Fimbrial antigen or colonisation factor antigens (CFAs)determine species specificity

**Fimbrial adhesins allow bacteria to attach to mucosal surfacesin the small intestine and lower urinary tract; this prevents expulsion by peristalsis and flushing of urine

***Fimbrial adhesins allow bacteria to attach to mucosal surfacesin the small intestine and lower urinary tract; this prevents expulsion by peristalsis and flushing of urine

**K88 (F4) is associated with adhesion to the small intestinal mucosa of pigs

***K88 (F4) is associated with adhesion to the small intestinal mucosa of pigs

**K99 (F5) associated with adhesion in pigs and cattle (these fimbrial adhesins were originally thought to be capsular (K) antigens)

***K99 (F5) associated with adhesion in pigs and cattle (these fimbrial adhesins were originally thought to be capsular (K) antigens)

**The fimbrae are encoded by plasmids

***The fimbrae are encoded by plasmids

**These strains carry a plasmid which encodes an enterotoxin

***These strains carry a plasmid which encodes an enterotoxin

**Two types of enterotoxin: heat-labile (LT) and heat-stable (ST) toxins

***Two types of enterotoxin: heat-labile (LT) and heat-stable (ST) toxins

**The plasmids which produce these toxins are responsible for the pathogenicity of these strains

***The plasmids which produce these toxins are responsible for the pathogenicity of these strains

**LT is an oligometric toxin composed of an enzymatically-active A subunit (30KDa; 2 fragments - A1 and A2) and 5 identical B subunits (12KDa) forming the binding portion (B oligomer)

***LT is an oligometric toxin composed of an enzymatically-active A subunit (30KDa; 2 fragments - A1 and A2) and 5 identical B subunits (12KDa) forming the binding portion (B oligomer)

**It attaches to the brush border of the epithelial cells of the small intestine

***It attaches to the brush border of the epithelial cells of the small intestine

**LT causes ADP-ribosylation of the stimulatory subunit of guanine nucleotide binding proteins of the adenylate cyclase complex in eukaryotic cell membranes

***LT causes ADP-ribosylation of the stimulatory subunit of guanine nucleotide binding proteins of the adenylate cyclase complex in eukaryotic cell membranes

**This causes irreversible activation of adenylate cyclase in target cells

***This causes irreversible activation of adenylate cyclase in target cells

**This raises the cAMP level and causes hypersecretion of water and chloride ions into the lumen of the small intestine and inhibits reabsorption of sodium

***This raises the cAMP level and causes hypersecretion of water and chloride ions into the lumen of the small intestine and inhibits reabsorption of sodium

**Clinical signs:

**Clinical signs:

**The gut becomes distended with fluid and a [[Intestines - diarrhoea#Secretory Diarrhoeas|secretory diarrhoea]] which lasts several days results

***The gut becomes distended with fluid and a [[Intestines - diarrhoea#Secretory Diarrhoeas|secretory diarrhoea]] which lasts several days results

**Watery diarrhoea, dehydration, acidosis, death

***Watery diarrhoea, dehydration, acidosis, death

**Immunuty:

**Immunuty:

**LT is antigenic

***LT is antigenic

**Immunity is developed via production of antibody to LT protein and fimbrial antigen

***Immunity is developed via production of antibody to LT protein and fimbrial antigen

**Parenteral vaccination of pigs and cattle protects offspring from scours via antibody production in the colostrum (passive immunity)

***Parenteral vaccination of pigs and cattle protects offspring from scours via antibody production in the colostrum (passive immunity)

**ST is not immunogenic; it is small, with only 19 amino acids

***ST is not immunogenic; it is small, with only 19 amino acids

**ST activates guanylate cyclase in enteric epithelial cells, stimulating fluid secretion

***ST activates guanylate cyclase in enteric epithelial cells, stimulating fluid secretion

*Enteropathogenic ''E. coli'' (EPEC):

*Enteropathogenic ''E. coli'' (EPEC):

**Possess ''E. coli'' adherence factor plasmid

**Possess ''E. coli'' adherence factor plasmid