E. Coli

• Pathotypes of diarrheagenic E. coli

  • Enterotoxigenic E. coli (ETEC)
  • Enteropathogenic E. Coli (EPEC)
  • Enteroinvasive E. coli (EIEC)
  • Enterohemorrhagic E. coli (EHEC)
  • Enteroaggregative E. coli (EAEC or EAggEC)
• Enterotoxigenic E. coli (ETEC)

  • Watery, non-inflammatory diarrhea
  • Non-bloody
  • Non-mucoid
  • Accompanied by mild abdominal cramps; usually without vomiting or fever
  • Resembling cholera
• Enteropathogenic E. Coli (EPEC)

  • Watery diarrhea
  • With mucus
  • Without gross blood
  • Also characterized by low-grade fever, malaise, and vomiting
• Enteroinvasive E. coli (EIEC)


  • Watery diarrhea
  • With fever and abdominal pain
  • Some patients present with dysentery, with very little stool
  • Much blood and mucus
  • Closely resembling shigellosis
• Enterohemorrhagic E. coli (EHEC)

  • E. coli O157:H7 — the most common involved serotype
  • Associated with epidemic and sporadic diarrhea
  • Developed countries
  • Reservoir- cattle or cow's
  • Transmission- Bovine fecal contamination
  • Source- ground beef, hamburgers, apple cider, bean sprouts and spinach
• Enteroaggregative E. coli (EAEC or EAggEC)


  • Watery, persistent diarrhea occurring more than 14 days in duration
  • With low grade fever and little or no vomiting
  • White blood cells and red blood cells are typically absent from the stool
• Weanling diarrhea


  • Among children in tropical and subtropical climates
  • Developing countries
  • When they are being weaned off nursing and start to take food and drinks other than mother's milk
• Traveler's diarrhea


  • Montezuma's revenge, Delhi belly, or turista
  • When a person eats food, or drinks water contaminated with ETEC, esp. during travel to developing countries, to an area with poor public hygiene, inadequate sanitation, or reduced availability of sources of potable water
• Infantile diarrhea


  • Usually less than 2 years of age
  • Diarrheal outbreaks occurring in hospital nurseries and daycare center
  • Cases in adults are rarely seen
• Hemorrhagic colitis


  • Watery diarrhea that progresses to bloody diarrhea
  • Stool does not contain leukocytes
  • Patients typically have little or no fever
  • Abdominal pain is common
• Hemolytic Uremic Syndrome (HUS)


  • Thrombotic disease of kidney microvasculature in which the endothelial cell is primary site of damage
  • Defined by triad of feature: Microangiopathic hemolytic anemia, Thrombocytopenia, Acute renal failure
  • Associated with diarrhea in persons of all ages in developing countries
  • Occurs predominantly in infants
  • Is increasingly recognized as a cause of traveler's diarrhea
• Pili (fimbriae)


  Facilitate attachment to the intestinal epithelium by binding to specific carbohydrate receptors on the intestinal microvilli
• Heat-labile toxin (LT)


  • Similar in structure and action to cholera toxin (choleragen) from Vibrio cholerae
  • An A/B toxin composed of A subunit and 5 identical B subunits arranged in a ring
  • A moiety: Enzymatic active portion, Activates cellular adenylate cyclase, causing an increase in the conversion of adenosine triphosphate cyclic adenosine monophosphate (cAMP)
  • B moiety: Binding portion, binds strongly to the epithelial cells of the small intestine, Facilitates the entry of A subunit into the cell
• Heat-stable toxin (ST)


  • Stimulates guanylate cyclase, causing increased production of cyclic guanosine monophosphate (cGMP)
  • Intracellular accumulation inhibits intestinal fluid uptake, resulting in hypersecretion
• Most persons living in endemic regions are resistant to the ETEC disease because they have developed antibodies that neutralize toxin, which plays havoc with travelers to these areas
• Bundle-forming pili (BFP)


  • Encoded by a plasmid, EPEC adherence factor EAF
  • Fimbriae produced by EPEC strains which tend to aggregate and form bundles
  • Mediate initial, non-intimate adherence of the bacteria with the surface of the enterocytes
• Locus of enterocyte effacement (LEE)


  • Encoded by chromosomal locus
  • Promotes intimate or tight adherence of the bacteria to the enterocytes
  • Extensive rearrangement of host cell *actin occurs in the vicinity of the adherent bacteria resulting in the formation of a cup-like pedestal structure under the bacteria, indenting the cell membrane and causing effacement, i.e.,localized destruction, of the microvilli
  • This causes the loss of the absorptive capacity of mucosal cells, thus diarrhea occurs
• Invasion of intestinal epithelial cells

  • Lysis of the phagosomal vacuole
  • Movement through the cytoplasm
  • Ultimately spreading to adjacent epithelial cells
• EIEC strains are characteristically nonmotile and lactose-negative (like Shigella); in contrast to other strains of E. coli which are motile and ferment lactose
• Attaching-and-effacing histopathology


  By binding tightly to cells and produce the same A/E phenomenon seen with EPEC strains
• Cytotoxins


  • Called Shiga toxins (previously called the shiga-like toxins)
  • Identical to the Shiga toxin (Stx) produced by Shigella dysenteriae type I
  • 2 types: Stx1 and Stx2
  • A single EHEC strain may express Stx1 only, Stx2 only, or both toxins or even multiple variants of Stx2
  • Shiga toxins are also called verotoxins or vero cytotoxins, derived from the observation that these are cytotoxic for Vero cells (African Green monkey kidney cells)
• Aggregative adherence fimbriae (AAF)


  • Flexible, bundle-forming fimbrial structures
  • Facilitate initial colonization
• Mucus biofilm


  • Enhanced mucus production traps bacteria in biofilm producing the characteristic layering of the bacteria described as a pile of stacked-brick configuration
  • Promotes persistent colonization and perhaps nutrient malabsorption
• Enteroaggregative ST-like toxin (EAST1)


  A cytotoxin which results in damage to intestinal cells
• Escherichia coli


  Common name: Colon bacillus
• Escherichia coli


  • Habitat: Normal flora in the large intestine; may colonize the vagina and urethra
  • Transmission: Acquired during birth and by fecal-oral route
• Urinary tract infection


  1. Commonly caused by E. coli, in approximately 90% of cases

  2. Results from endogenous spread of the bacteria from the large intestine as resident flora, and mechanically introduced into the urethra (e.g., careless personal hygiene, sexual intercourse, or catheterization)

  3. Colonization facilitates the ascent of bacteria from the urethra into the bladder causing cystitis

  4. Invading bacteria pass up the ureters to kidney, cause pyelonephritis
• Urinary tract infection


  • Occurs primarily in women, a finding attributed to 3 features: Short urethra, Proximity of the urethra to the anus, Colonization of the vagina by members of the fecal flora
• Signs and symptoms of urinary tract infection

  • Urinary frequency - urge to pass urine more often than usual
  • Dysuria - painful urination
  • Hematuria - the presence of blood in urine
  • Pyuria - presence of leukocytes, commonly referred to as pus, in urine
  • Flank pain - pain in one side of the body between the upper belly area (abdomen) and back associated with upper tract infection, a sign of kidney involvement
• None of these symptoms or signs is specific for E coli infection
• P pili (P fimbriae)


  • Primary virulence factor of E. coli to cause UTIs
  • Allow the bacteria to attach to the urinary epithelial mucosa and not be washed out with urine flow
  • Named for their ability to bind to and agglutinate human RBCs carrying the P blood group antigen
• Endotoxin


  • Resides in cell wall and consists of the lipid A of the LPS
  • Responsible for much of the morbidity and mortality resulting from infections associated with these bacteria
• Hemolysin


  • Cytolysin that creates pores in eukaryotic cell membranes
  • Inhibits phagocytosis and chemotaxis of certain white blood cells
• Aerobactin


  • A siderophore, .i.e., iron chelating agent, enabling E. coli to bind and transport iron for use by bacteria in iron-poor environments such as the urinary tract
• Capsular polysaccharide


  • The determinant of the K antigen
  • Is antiphagocytic and inhibits the opsonizing and lytic activities of complement because of the identity of the capsular polysaccharides and the host carbohydrates
• Neonatal meningitis and septicemia

  1. E. coli - a major cause of meningitis and septicemia and meningitis among newborns, along with Group B streptococci

  2. Acquired by newborns by vertical transmission from the birth canal just before or during delivery, when the mother's vagina is heavily colonized or infection may also result if contamination of the amniotic fluid occurs
• K1 antigen (capsular polysaccharide)

  • A polymer of sialic acid possessed by approximately 80% of E. coli from meningitis cases
  • Antiphagocytic and provides some resistance against the usual sensitivity of E. coli to complement-mediated lysis
  • Cross-reacts with the group B capsular polysaccharide - of Neisseria meningitidis
  • Does not stimulate antibody production antibodies because of its similarity to host sialic acid polymers
• S fimbriae


  • Bind to vascular endothelium and epithelial lining of brain tissue
• Siderophore


  • Allows the bacteria to chelate iron
• E. coli is an important cause of extraintestinal infections, mostly nosocomial i.e., in hospitalized patients whose normal defense mechanisms have been breached. These include wound infections, and pneumonia