Felis ISSN 2398-2950

Escherichia coli

Introduction

Classification

Taxonomy

• Family: Enterobacteriaceae.
• Genus: Escherichia.

Classification of enteritis-causing E. coli strains

• Enterotoxigenic E. coli ( ETEC): have fimbrial adhesins, produce enterotoxin, cause neonatal colibacillosis.
• Enteropathogenic E. coli (EPEC): do not produce enterotoxins or Shiga-like toxins, cause enteritis/diarrhea and colisepticemia by other mechanisms.
• Attaching and effacing E. coli (AEEC): colonize small intestine, attach to target cells and kill them, Shiga-like toxins, isolated from calves and rabbits with enteric disease.

Etymology

• Escherichia: named after Theodor Escherich, who named the type species of the genus.

Active Forms

Clinical Effects

Epidemiology

Habitat

• Pathogenic and non-pathogenic strains of E. coli inhibit the lower gastrointestinal tract.
• Also abundant in the environment of animals.

Lifecycle

• Reproduces by binary fission, usually in the gastrointestinal tract of the host.
• Conjugation may occur with other bacteria to allow exchange of plasmids, which may bear toxin genes, and other transposable elements.

Transmission

• Fecal oral route.

Pathological effects

Predisposers

• Insufficient passive (colostral) immunity, ie neonates.
• Poor environmental hygiene   →   build-up of pathogenic strain   →   may overcome normal levels of passive immunity.
• Intensive farming methods   →   rapid transmission of pathogenic strains.
• Age - (less than 1 week old) because:
  • Normal flora not yet established.
  • Immature immune system.
  • Receptors for the adhesins of E. coli only present for first week of life (calves) and first 6 weeks of life (piglets).
• Stress factors, eg changed environment and diet in recently weaned pigs.
• Heavy grain diets - allowing massive colonization of enterotoxigenic, K88 and K99 strains ofE. coli.
• Recent change in feed and period of rapid growth, eg edema disease in pigs.

Virulence factors of pathogenic E. coli strains

• Capsular polysaccharide (K antigen).
• Endotoxin (Lipid A) associated with septicemia and the toxemia of coliform mastitis.
• Certain fimbriae are protein adhesins.
• Alpha and beta hemolysins.
• Siderophores.
• Heat-labile and heat-stable enterotoxins (LT enterotoxin is antigenically related to the cholera toxin).
• Verotoxin or Shiga-like toxins - inhibit protein synthesis in host cells. Important in edema disease and in neonatal calves and piglets.

Opportunistic infections

• E. coli strains, normally regarded as non-pathogenic can cause opportunistic infections, eg mastitis and metritis.

Other Host Effects

• Predominant facultative species in large intestine.

Diseases associated with E. coli

Dog and cat

• Neonatal colisepticemia.
• Pyometra  Pyometra.
• Urinary tract infection.

Pig

• Neonatal diarrhea.
• Colisepticemia.
• Piglet meningitis.
• Edema disease.
• Coliform mastitis.
• Mastitis-metritis-agalactia (MMA) syndrome.

Cattle

• White scour.
• Colisepticemia.
• Joint ill.
• Coliform mastitis.

Sheep

• Colibacillosis and colisepticemia.
• 'Watery mouth'.
• Coliform mastitis.

Poultry

• Omphalitis.
• Colisepticemia.
• Coligranuloma.

Other species

• Colibacillosis and colisepticemia.

Control

Control via animal

• Sound husbandry - the dam should be exposed to the local strains before parturition.
• Some vaccines are available.
• Maternal exposure to E. coli, either natural or artificial, allows for antibodies to be produced by the dam and secreted into the colostrum and milk.
• Commercially produced preparations containing monoclonal antibodies to adhesins can be given orally to the neonate.

Control via chemotherapies

• Most E. colis trains are sensitive to a wide range of antibiotics but resistance, often plasmid-mediated is frequently encountered.
• The use of antimicrobials to treat the diarrhea is controversial.

Vaccination

• Some are available.

Diagnosis