Microbiology, parasitology & COVID-19

Gram negative bacteria

E. coli

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Last staff update: 5 October 2020

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PubMed Search: Escherichia coli [title]

Christopher S. Hale, M.D.
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Cite this page: Hale C. E. coli. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/microbiologyescherichiacoli.html. Accessed June 1st, 2023.
Definition / general
  • Gram stain: negative
  • Morphology: bacilli
  • Facultative anaerobe
  • Normal component of bowel microflora
  • Glucose fermenting, oxidase negative, nitrate reducer
  • Motile
  • Urinary tract infections
  • Bacteremia
  • Meningitis
  • O157 : H7 strain associated with Hemolytic Uremic Syndrome (TTP / HUS) from contaminated beef

  • Diarrhea-producing strains:
    • Shiga Toxin producing E. coli (STEC)
    • Enterohemorrhagic E. coli (EHEC)
    • Enterotoxin producing E. coli (EPEC)
    • Enteroinvasive E. coli (EIEC)
    • Enteropathogenic E. coli (EPEC)
    • Enteroaggregative E. coli (EAEC)
  • Culture conditions:
    • 37, MacConkey agar (selective for gram negative bacteria)

  • Gram negative
  • IMViC (Indole, Methyl Red, Voges-Proskauer, Citrate) pattern: (+), (+), (-), (-)
  • Non - O157 strains ferment lactose on MacConkey agar, O157 serotypes lose ability to ferment sorbitol
  • No selective culture medium exists for non - O157 strains; test for Shiga toxin using EIA (enzyme immunoassay) or use chromogenic agar
  • Acid/Acid, gas - producer pattern on Triple Sugar Iron (TSI) slant test
  • Urinary tract infections traditionally treated with:
    • Fluoroquinolones
    • Cephalosporins
    • Trimethoprimsulfamethoxazole

  • Resistance to fluoroquinolones and cephalosporins emerging in extraintestinal E. coli (Expert Rev Anti Infect Ther 2012;10:1165)
  • Bacteremia often treated with empirical combination antibiotic regimen directed against gram negative bacteria (i.e., B - lactam plus aminoglycoside or fluoroquinolone) (Antimicrob Agents Chemother 2010;54:1742)
  • Plasmid - mediated AmpC B - lactamases (e.g., CMY), extended - spectrum B - lactamases (e.g., CTX - M), and carbapenemases seen increasingly (Front Microbiol 2012;3:9)
Gross description
  • White
Molecular / cytogenetics description
Differential diagnosis
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