Difference between revisions of "Escherichia coli"

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<big><center>[[Enterobacteriaceae|'''BACK TO ENTEROBACTERIACEAE''']]</center></big>
 
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<big><center>[[Bacteria|'''BACK TO BACTERIA''']]</center></big>
===''Eschericia coli'' (''E. coli'') overview===
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<big><center>[[Infectious agents and parasites|'''BACK TO INFECTIOUS AGENTS AND PARASITES''']]</center></big>
[[File:Ecoli.jpg|200px|right]]
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* Enterotoxigenic ''E.coli'' contributes to [[Intestines - Catarrhal Enteritis#Undifferentiated Neonatal Calf Diarrhoea|undifferentiated neonatal calf diarrhoea]], a mixed viral enteritis in calves.
*Member of ''Enterobacteriacae'' family of Gram-negative bacilli
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* [[Intestines - Catarrhal Enteritis#Colibacillosis|Colibacillosis]].
*'''Facultative anaerobe'''
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* [[Intestines - Inflammatory Bowel Disease And Related Conditions#Histiocytic Ulcerative Colitis|Histiocytic ulcerative colitis]] in the dog and cat.
*One of predominant bacterial species in colonic flora
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* Causes [[Intestines - diarrhoea#Secretory Diarrhoeas|secretory diarrhoea]]
*Colonisation of intestinal tract from environmental sources shortly after birth
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* Causes [[Peritoneal cavity - inflammatory#In dogs|peritonitis in dogs]] and [[Peritoneal cavity - inflammatory#In pigs|peritonitis in pigs]]
*Abundant in the environment
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* In [[Bones - inflammatory#Osteomyelitis|osteomyelitis]]
*Most strains have low virulence
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*In neonatal [[Joints - inflammatory#Infectious arthritis|polyarthritis]] of calves
*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 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
 
 
 
 
 
===Pathogenesis===
 
 
 
*<u>Virulence factors</u> 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|'''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
 
*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:
 
**'''Urogenital tract infections'''
 
***Most common organism infecting urinary tract
 
***Ascending infections of urinary tract
 
***Causes pyometra in the dog and cat and [[Pyelonephritis|pyelonephritis]]
 
***Cystitis in the bitch
 
***Prostatitis in dogs via opportunistic infection
 
***Colonisation of mucosa aided by fimbriae
 
**'''Mastitis'''
 
***Opportunistic infection of mammary glands of sows and cows
 
***Endotoxaemia in the acute form often fatal
 
***Death within 24-48 hours during peracute disease
 
***Animals depressed with sunken eyes
 
**[[Colibacillosis|'''Colibacillosis''']]:
 
***Avian:
 
****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 [[:Category:Mycoplasmas|''mycoplasma'']] 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
 
**[[Oedema Disease|'''Oedema disease of pigs''']]:
 
 
 
**'''Watery mouth of lambs''':
 
***Affects lambs under three days old
 
***Lack of colostrum allows collonisation and overgrowth of ''E. coli'' in the small intestine
 
***Systemic invasion by ''E. coli''
 
***Absorption of endotoxin leads to death
 
***Severe depression, anorexia, salivation and abdominal distension
 
***Morbidity and mortality high
 
** [[Inflammatory Bowel Disease#Histiocytic Ulcerative Colitis|Histiocytic ulcerative colitis]] in the dog and cat.
 
** Causes [[Peritonitis - Cats and Dogs|peritonitis in dogs]] and [[Peritonitis#In pigs|peritonitis in pigs]]
 
**Found in [[Osteomyelitis|osteomyelitis]]
 
**Associated with neonatal [[Infectious Arthritis#In Cattle|polyarthritis of calves]]
 
**In [[Deep Pyoderma|deep pyoderma]]
 
**Found in [[Infectious Arthritis#In Horses|arthritis of horses]]
 
 
 
==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 [[Haemorrhage#Dysentery|dysentery]]
 
 
 
 
 
*'''Enterotoxigenic ''E. coli'' (ETEC)''':
 
**General:
 
*** Contributes to [[Calf Diarrhoea, Undifferentiated Neonatal|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 '''fimbriae 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'''
 
*****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
 
*****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 [[Diarrhoea#Secretory Diarrhoeas|secretory diarrhoea]] which lasts several days results
 
***Watery diarrhoea, dehydration, acidosis, death
 
**Immunity:
 
***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
 
 
 
 
 
*'''Enteropathogenic ''E. coli'' (EPEC)''':
 
**Attaching and effacing strains of ''E. coli''
 
**Attach to small intestinal epithelial cells and cause necrosis of enterocytes and stunting and fusion of villi
 
**Possess ''E. coli'' adherence factor plasmid
 
**An adhesin, intimin is required for attachment to enterocytes
 
**Secrete signalling proteins that activate a tyrosine kinase, causing rearrangement of cytoskeletal proteins and effacement of microvilli
 
**Intracellular calcium levels increase and production of protein kinase C causes loss of chloride ions and water from the intestinal epithelial cells
 
**Diarrhoea results
 
 
 
 
 
*'''Enteroinvasive ''E. coli''''':
 
**Cause colisepticaemia in calves during their first week of life; occasionally in lambs, piglets and puppies
 
**Infection via ingestion or umbilicus; inadequate colostrum increases susceptibility
 
**Invade epithelial cells of small intestine by inducing endocytosis
 
**Traverse gut wall to lamina propria and enter lymphatics
 
**Resistant to complement-mediated killing
 
**Bacteraemia or septicaemia and endotoxaemia
 
**Widespread petechial haemorrhages of organs and serosa
 
**Abscesses, pneumonia in long term
 
**Death occurs in absense of treatment
 
 
 
 
 
*'''Enterohaemorrhagic ''E. coli''''':
 
**Possibly carried by cattle
 
**Produce shiga-like toxin, a vero toxin
 
**Plasmid-coded fimbriae important for virulence
 
**Intimin produced allowing intimate attachment to intestinal epithelial cells
 
**Strains do not product LT or ST and are not enteroinvasive
 
**Attaching and effacing lesions, unrelated to toxin production
 
**[[Disseminated Intravascular Coagulation|Disseminated intravascular coagulation]] and thrombus formation
 
**''E. coli'' O157:H7 causes haemorrhagic collitis-haemolytic uraemic syndrome in humans
 
 
 
 
 
*'''Cytotoxin necrotising factor-producing ''E. coli'''''
 
**Infrequently cause diarrhoea in calves, pigs and humans
 
**Important virulence factors include toxin and fimbriae
 
 
 
==in cattle==
 
 
 
 
 
*Neonatal polyarthritis:
 
 
 
**[[Escherichia coli|'''''Coliforms''''']]
 
***Localises in joints and meninges in severe non-fatal neonatal colibacillosis
 
***May remain as chronic arthritis in larger joints
 
 
 
[[Category:Enterobacteriaceae]]
 
[[Category:To_Do_-_Bacteria]]
 

Revision as of 14:55, 5 October 2007