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Escherichia coli

March 12, 2013


Image Source: Keep Our Food Safe

General Characteristics:

  • common specimens are urine, stool, and cerebral spinal fluid
  • causes a wide range of infections
  • used as a fecal marker in water purification tests
  •  most strains are motile
  • most possess O, K, and H antigens
  • serotyping is helpful in identification of strains in outbreaks

Pathogenesis and Infectious Disease:

  • divided into categories based on:
    • virulence factors
    • clinical manifestation
    • epidemiology
    • different O and H serotypes
  • Nephropathogenic E. coli: NPEC

    • most common cause of UTIs in humans
    • originate from the large intestine
    • can be introduced by catheter placement
    • can attach to mucosa of urinary tract – pili allow them to attach and not be washed away by urine flow
  • Enterotoxigenic E. coli: ETEC
    • diarrhea of infants/adults in tropical/subtropical climates
    • in the US, #1 cause of diarrhea – “traveler’s diarrhea”
    • spread via consumption of contaminated food or water due to inadequate sanitation practices
    • high dose of organisms needed in immunocompetent host
    • release toxins (enterotoxigenic) – this is what causes disease
    • self-limiting disease causes watery diarrhea, cramps and sometimes nausea with no fever or vomitting
  • Enteroinvasive E. coliEIEC
    • produces dysentery with direct penetration, invasion, and destruction of the intestinal mucosa
    • very similar to disease produced by Shigella spp.
    • occurs in adults and children (developing countries)
    • transmission is person-to-person via fecal-oral route
    • fever, severe cramps, malaise, and watery diarrhea
    • use DNA probes to screen stool samples for EIEC
  • Enteropathogenic E. coli: EPEC
    • causes infantile diarrhea and diarrhea in outbreaks in hospital nurseries and daycares but rarely seen in adults
    • has adhesive property that allows organisms to stick to mucosa
    • disease presents as low-grade fever, malaise, vomiting, and diarrhea
    • stool typically contains large amounts of mucus, but apparent blood is absent
    • diagnosis usually based on physician concerns
  • Enterohemorrhagic E. coli: EHEC
    • most famous serotype: O157:H7 which is associated with hemorrhagic diarrhea, colitis, and hemolytic uremic syndrome (HUS)
    • watery diarrhea that progresses to bloody diarrhea with abdominal cramps, a low-grade fever or absence of fever
    • stool contains no leukocytes – different from Shigella spp. or EIEC infections
    • infection is potentially fatal – especially children and the elderly
    • processed and indercooked meats (hamburger), unpasteurized dairy products and apple cider, bean sprouts, and spinach have all been vectors
  • Enteroadherent (Enteroaggregative) E. coli: 
    • includes diffusely adherent (DAEC) and the enteroaggregative (EAEC) strains
    • DAEC is associated with diarrheal syndromes and UTIs
    • EAEC diarrhea : watery diarrhea, vomiting, dehydration, and occasionally abdominal pain
    • symptoms persist for 2 or more weeks
  • Extraintestinal Infections:
    • one of the most common causes of septicemia and meningitis among neonates – about 40%
    • newborn acquires infection in the birth canal or from infected amniotic fluid
    • also one of the significant organisms isolated in blood cultures from adults – urogenital tract or a GI source (surgical complications such as ruptured appendix)

Treatment and Prevention:

  • usually resistant to penicillins, erythromycin, clindamycin, vancomycin, and ampicillin

Test Results:

  • Lactose Fermentation (MAC) – positve (pink colonies)
  • HE – yellow colonies
  • XLD – yellow colonies
  • H2S production : negative
  • IMViC :   +/+/-/-
  • Urea : negative
  • TSI : A/A
  • Motility : positive
  • ONPG : postive
  • Lysine : positive
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