E.coli

PHYSIOLOGY & STRUCTURE:
  • Gram-negative, facultative anaerobic rods, Peritrichous flagella
  • Fermenter; oxidase negative
  • Non-pathogenic amoebae
  • Preferred bacteriological indicator of faecal contamination of water
  • Outer membrane makes the organisms susceptible to drying
  • Lipopolysaccharide consists of outer somatic O polysaccharide, core polysaccharide (common antigen), and lipid A (endotoxin)
  • E.coli gets attached to a surface with the help of lectin( P blood group antigen binding Microbial adhesion proteins)
VIRULENCE:
  • Endotoxin
  • Permeability barrier of outer membrane
  • Adhesins :e.g., colonization factor antigen, Dr adhesins,K-88 antigen , K-99 antigen
  • Exotoxins :e.g.,
  • Heat-stabile and
  • Heat-labile enterotoxins(c-AMP mediated);
  1. Shiga toxins STEC
  2. O157:H7 (common)is negative (clear colonies) on sorbitol MacConkey agar & MUG tests
  • non-O157 serotypes may be sorbitol positive
  • Invasive capacity
DISEASES:
  • Bacteremia , septicemia (within 2month)
  • Ascending cholangitis
  • Urinary tract infection (most common cause of bacterial UTIs & catheter induced UTI); limited to bladder (cystitis) or can spread to kidneys (Emphysematous pyelonephritis) or prostate (prostatitis)
  • Malakoplakia often associated with urinary tract infection by E.coli(shows characteristic polygonal granular cells ,Michaelis gutmann bodies, leukocytes and few RBCs )
  • Neonatal meningitis (usually with strains carrying the K1 capsular antigen)
  • Intraabdominal infections (associated with intestinal perforation)

Organism Site of Action Disease Pathogenesis
Enteropathogenic E. coli (EPEC) Small intestine Infant diarrhea in underdeve lopedcountries;
watery diarrhea andvomiting, nonbloody stools
Plasmid-mediatedadheres to the mucosa of upper small intestine and causes
disruption of the brush border microvilli ( adhesion to HEP-2 cells)histopathology with disruption ofnormal microvillus structureresulting in malabsorption anddiarrhea
Enterotoxigenic E. coli (ETEC) Small intestine Traveler's diarrhea;Transmitted by feco-oral route and through fomites: infant diarrheain developing countries;
waterydiarrhea, vomiting, cramps,nausea, low-grade fever
Plasmid-mediated, heat-stableand/or heat-labile enterotoxinsthat stimulate hypersecretion offluids and electrolytes
Enterohemorrhagic E. coli (EHEC) Large intestine Initial watery diarrhea, followed bygrossly bloody diarrhea i.e. hemorrhagic colitis(O157:H7 is the serotype) with abdominal cramps; little or nofever; may progress to hemolytic
uremic syndrome (HUS),
Mediated by cytotoxic Shigatoxins (Stx-1, Stx-2), which disruptprotein synthesis; A/E lesions withdestruction of intestinal microvillusresulting in decreased absorption,Also produces Verocytotoxin
Enteroinvasive E. coli (EIEC) Large intestine Disease in underdeve loped countries; fever, cramping, wate rydiarrhea; may progress todys ntery with scant, bloody
stools
Plasmid-mediated invasion anddestruction of epithelial cells liningcolon(shows Sereny test is positive)
Enteroaggregative E. coli (EAEC) Small intestine Infant diarrhea in unde rdeveloped countries; traveler's diarrhea;
persistent watery diarrhea with vomiting, dehydration, and low-grade fever
Plasmid-mediated aggregativeadherence of rods ("stackedbricks")
with shortening ofmicrovilli, mononuclear infiltration,and hemorrhage;
decreased fluidabsorption
DIAGNOSIS:
  • Organisms grow rapidly on most culture media(MacConkey Agar plate)
  • EMB agar—Selective AND Differential
  • E. coli forms blue-black colonies with a green metalic sheen. (due to lactose fermentation)
  • Methods for detection of ETEC enterotoxins

Assay LT ST
In vivo tests ±+ +?
Ligated rabbit deal loop
Read at 6 hours
Read at 18 hours
Infant rabbit bowel + +
Infant mouse intragastric
(4 hours)
- +
Adult rabbit skin
(vascular permeability)
+ ?
In vitro tests
Tissue culture tests
Rounding of Y1 mouse adrenal cells - -
Elongation of chinese hamster ovary
(CHO) cells
+ ?
Serological tests
ELISA + (ST-ELISA withmonocolonial antibody)
Passive agglutination tests, passive immune hemolysis,
precipitin (Eiken's) test
+ -
Genetic tests
DNA probes + +
TREATMENT, PREVENTION & CONTROL:
  • Antibiotic therapy is guided by in vitro susceptibility tests
  • Lactoferrin binds to iron and makes it unavailable for E.coli and acts a defence mechanism against infections
  • Appropriate infection-control practices are used to reduce the risk of nosocomial infections (e.g., restricting use of antibiotics, avoiding unnecessary use of urinary tract catheters)
  • Maintenance of high hygienic standards to reduce the risk of exposure to gastroenteritis strains
  • Proper cooking of beef products to reduce risk of EHEC infections
Exam Question
  • Malakoplakia often associated with urinary tract infection by E.coli(shows characteristic polygonal granular cells ,Michaelis gutmann bodies, leukocytes and few RBCs )
  • EC O157:H7, shiga toxin-producing strain of E. coli can be distinguished from other strains of E.coli by using Sorbitol on MacConkey agar
  • O 157:H7 serotype of E.coli is the causative agent of hemorrhagic colitis
  • E.coli is an aerobe and facultative anaerobe with peritrichate flagella
  • Enterotoxigenic E. coli (ETEC) are Transmitted by feco-oral route and through fomites
  • Entero-toxigenic E.coli (ETEC) is most commonly responsible for traveller’s diarrhea
  • Lactoferrin binds to iron and makes it unavailable for E.coli and acts a defence mechanism against infections
  • E.coli is most commonly responsible for ascending cholangitis
  • Enterohemorrhagic E. coli (EHEC) causes diahorrea hemolytic uremic syndrome (HUS),produces Verocytotoxin
  • Labile toxin of E.coli can be detected by there incubation into Ligated rabbit deal loop,Infant rabbit bowel,Adult rabbit skin (vascular permeability),Elongation of chinese
  • hamster ovary (CHO) cells
  • Heat labile E.coli toxin is mediated by c-AMP
  • E.coli gets attached to a surface with the help of lectin( P blood group antigen binding Microbial adhesion proteins)
  • Most common cause of UTI in young female is E.coli
  • vaccines against Adhesins :e.g., colonization factor antigen, Dr adhesins,K-88 antigen , K-99 antigen can preventattachment of diarrhoeagenic E.coli to the specific receptors in the gastro-intestinal tract.
  • The mechanism of action of Enteropathogenic E.coli is by Adherance to enterocytes
  • Non-pathogenic amoebae is E.coli
  • Most common cause of sepsis in India within 2 months is E.coli
  • The most common bacterial cause for diarrhea in children in India is E.coli
  • The common organism isolated in Emphysematous pyelonephritis is E.coli
  • E.coli is the Most common agent causing catheter induced urinary tract infection
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