Difference between revisions of "Escherichia coli"
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***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 | ||
| + | ***ST activates guanylate cyclase in enteric epithelial cells, stimulating fluid secretion | ||
**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 | ||
| Line 111: | Line 112: | ||
***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 | ||
| − | |||
*Enteropathogenic ''E. coli'' (EPEC): | *Enteropathogenic ''E. coli'' (EPEC): | ||
**Possess ''E. coli'' adherence factor plasmid | **Possess ''E. coli'' adherence factor plasmid | ||
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**Cause attching and effacing lesions in the gut, with necrosis of enterocytes and stunting and fusion of villi | **Cause attching and effacing lesions in the gut, with necrosis of enterocytes and stunting and fusion of villi | ||
*Enteroinvasive ''E. coli'': | *Enteroinvasive ''E. coli'': | ||
| + | **Bacteraemia and septicaemia | ||
**Dysentry-like strains | **Dysentry-like strains | ||
**Invade epithelial cells by inducing endocytosis | **Invade epithelial cells by inducing endocytosis | ||
Revision as of 20:01, 8 February 2008
- Histiocytic ulcerative colitis in the dog and cat.
- Causes peritonitis in dogs and peritonitis in pigs
- In osteomyelitis
- In neonatal polyarthritis of calves
- In arthritis of horses
Eschericia coli (E. coli) overview
- Member of Enterobacteriacae family of Gram-negative bacilli
- Facultative anaerobe
- One of predominant bacterial species in colonic flora
- Colonisation of intestinal tract from environmental sources shortly after birth
- Abundant in the environment
- Most strains have low virulence
- Found in many non-specific, endogenous infections, eg. wound infections, upper respiratory tract infections, infections of the urinary tract, mammary glands and uterus and septicaemia
- An enteropathogen, causing neonatal diarrhoea in young animals and enteric colibacillosis
- Enterotoxigenic E. coli is the most common cause of diarrhoea in calves, lambs and pigs
- Pathogenic strains possess virulence factors allowing colonisation of mucosal surfaces
E. coli characteristics
- Usually motile with flagella and fimbriae
- Oxidase negative (do not possess cytochrome C oxidase)
- Grow on MacConkey agar (in presence of bile salts), producing pink colonies
- Haemolytic activity on blood agar characteristic of certain strains
- Lactose fermenter
- Reduce nitrates to nitrites and ferment glucose to produce acid and gas
- Possess a lipolysaccharide (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
Pathogenesis
- Virulence factors include capsules, endotoxin, enterotoxins and colonisation factors
- 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 realeased when bacteria die, and causes endothelial damage leading to disseminated intravascular coagulation and endotoxic 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
- 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
Extra-intestinal infection
- Soft tissue infections in adult animals
- Most common organism infecting urinary tract
- Causes pyometra in the dog and cat and pyelonephritis
- Acute mastitis in lactating animals
- Pathogenesis:
- Produces an alpha-haemolysin which may be cytotoxic
- Iron aquisition system
- K antigens prevent phagocytosis or mimic host antigens and resist complement
- Fimbriae permit adhesion to mucosal surfaces
- May enter blood to cause septicaemia
- Clinical infections:
- Avian colibacillosis:
- Septicaemia in newly-hatched chickens
- Infection enters via faecal contamination of the egg surface or via the ovary of the hen
- Infection enters via the respiratory tract
- A bacteraemia develops
- Acute colisepticaemia, subacute fibrinopurulent serositis or chronic granulomatous disease of the viscera
- Occurs in older birds via inhalation of E. coli in dust; respiratory infection spreads to the blood to cause acute colisepticaemia
- Airsacculitis, pericarditis and perihepatitis during acute phase
- Often secondary to virus or mycoplamsa infection or environmental stress
- Colisepticaemia:
- Systemic disease in young calves, piglets, foals, lambs
- Penetration of intestinal mucosa and entrance into the blood
- Invasive strains survive the host defences
- Virulence related to adhesive properties, complement resistance and ability for iron aquisition
- Ammonia, dust, viral infections and temperature changes enhance likelihood of disease
- Avian colibacillosis:
Intestinal infection
- E. coli is part of the flora of the large intestine, but is not usually found in the small intestine
- Some strains possess fimbrae which attach the bacteria to the small intestinal epithelium of particular animal species
- E. coli may cause diarrhoea via attaching and effacing lesions, where bacteria adhere intimately to the enterocyte, and cause localised effacement of the brush border microvilli; the epithelial erosion causes dysentery
- Enterotoxigenic E. coli (ETEC):
- General:
- Contributes to undifferentiated neonatal calf diarrhoea, a mixed viral enteritis in calves, also known as enteric colibacillosis
- Causes scours in pigs, calves and lambs
- 'Traveller's diarrhoea' in humans
- Pathogenesis:
- Oral infection, intestinal colonisation and toxin production
- 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
- 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)
- The fimbrae are encoded by plasmids
- These strains carry a plasmid which encodes an enterotoxin
- 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
- 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
- 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 raises the cAMP level and causes hypersecretion of water and chloride ions into the lumen of the small intestine and inhibits reabsorption of sodium
- ST activates guanylate cyclase in enteric epithelial cells, stimulating fluid secretion
- Clinical signs:
- The gut becomes distended with fluid and a secretory diarrhoea which lasts several days results
- Watery diarrhoea, dehydration, acidosis, death
- Immunuty:
- LT is antigenic
- 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)
- ST is not immunogenic; it is small, with only 19 amino acids
- General:
- Enteropathogenic E. coli (EPEC):
- Possess E. coli adherence factor plasmid
- An adhesin, intimin is required for attachment to enterocytes
- Cause attching and effacing lesions in the gut, with necrosis of enterocytes and stunting and fusion of villi
- Enteroinvasive E. coli:
- Bacteraemia and septicaemia
- Dysentry-like strains
- Invade epithelial cells by inducing endocytosis
- Traverse gut wall to lamina propria
- Enterohaemorrhagic E. coli:
- Possibly carried by cattle
- Produce shiga-like toxin, a vero toxin
- Attaching and effacing lesions, unrelated to toxin production
- Disseminated intravascular coagulation and thrombus formation
- E. coli O157:H7 causes haemorrhagic collitis-haemolytic uraemic syndrome in humans
- Cytotoxin necrotising factor-producing E. coli
- Oedema disease of pigs:
- Acute, frequently fatal enterotoxaemia of weaned pigs
- Associated with particular haemolytic serotypes of E. coli
- Verotoxin (Shiga toxin II e) released in the small intestine and carried in the bloodstream
- Haemolysin production
- Subcutaneous and subserosal oedema
- Peracute disease affecting particulary healthy piglets
- Mortality rate 30%-90%
- Antimicrobial treatment effectic if administered in time
- Haemorrhagic gastroenteritis:
- Watery mouth of lambs:
- Lack of colostrum allows collonisation and overgrowth of E. coli in the small intestine
- Absorption of endotoxin leads to death