10 Questions
What is the primary site of colonization of Enterotoxigenic E. coli in the bovine gastrointestinal tract?
Ileum
Which of the following virulence factors is responsible for the stimulation of a secretory response by intestinal crypt cells?
Enterotoxins
What is the primary factor that influences the expression of fimbriae in Enterotoxigenic E. coli?
pH
Which of the following statements is true about the susceptibility of calves to Enterotoxigenic E. coli?
Susceptibility is age-dependent according to the binding specificity of pili antigens to immature enterocytes
What is the recommended treatment for Enterotoxigenic E. coli diarrhea?
Oral electrolyte solutions containing acetate
What is the primary mechanism by which AEEC and STEC cause disease in calves?
By inducing cytotoxic damage to the intestinal mucosa
Which of the following E. coli serogroups are commonly associated with AEEC and STEC?
O5, O26, O118
What is the primary toxin produced by Shiga toxin–producing E. coli (STEC)?
Shiga toxin
What is the typical age range of calves affected by F5-positive ETEC?
4- to 12-week-old
What is the term used to describe AEEC that do not produce enterotoxins or Shiga toxin?
Enteropathogenic E. coli
Study Notes
Escherichia Coli (E. coli)
- E. coli are part of the normal flora of the bovine GI tract.
Pathogenic Strains of E. coli
- Possess virulence attributes that contribute to disease pathogenesis, including:
- Adhesins
- Enterotoxins
- Cytotoxins
- May be shed by adult cattle and transmitted to neonates through the fecal-oral route.
- Sick neonates can amplify environmental contamination through prolific fecal shedding.
Enterotoxigenic E. coli (ETEC)
- Possess two virulence factors:
- Fimbriae (pili)
- Enterotoxins
- F5 (K99) and/or F41 fimbriae mediate adherence.
- Thermolabile (LT) and thermostable (STa and STb) enterotoxins stimulate a secretory response in intestinal crypt cells.
- Expression of fimbriae is influenced by pH, with expression occurring at a pH of 6.5 or greater.
- The distal small intestine is the initial site of colonization, as the pH of intestinal fluid increases caudally, reaching the threshold at the ileum.
Characteristics of ETEC
- Bicarbonate-containing oral replacement fluids may favor the proliferation of ETEC, expression of the K99 antigen, and secretion of STa.
- Oral electrolyte solutions containing acetate are recommended for treatment of ETEC diarrhea.
- Most strains that cause diarrhea in neonatal calves produce STa heat-stable enterotoxin.
- The STa enterotoxin and F5 antigen are plasmid-mediated virulence factors.
- Susceptibility to ETEC is age-dependent, according to the binding specificity of pili antigens to immature enterocytes.
- Disease is typically observed in calves younger than 3 days of age, but concurrent infection with rotavirus may extend this window to 7-14 days of age.
- Intestinal cells of calves older than 2 days of age acquire natural resistance to F5 adhesion.
Attaching and Effacing E. coli (AEEC) and Shiga Toxin-Producing E. coli (STEC)
- AEEC and STEC cause diarrhea and dysentery in calves.
- Disease is mediated by cytotoxic damage to the intestinal mucosa.
- Lesions may be observed in the ileum, cecum, and descending colon.
- AEEC (verotoxin- or Hela toxin-producing) induce a mucohemorrhagic colitis, with petechial or ecchymotic hemorrhages in the wall of the colon and rectum.
- E. coli that carry this toxin often belong to O serogroups 5, 26, 111, 118, and 145.
- STEC serotypes associated with dysentery in calves include O5:H-, O26:H11, O111:H-, and O113:H21.
- Bovine STEC produce either STx1 or STx2, or both.
Learn about Escherichia Coli, its role in the bovine GI tract, and the characteristics of pathogenic strains, including enterotoxigenic E. coli. Understand the transmission and disease pathogenesis of E. coli.
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