Exercise 7

Cards (12)

  • Some distinct characteristics of family Enterobacteriaceae:
    • gram negative bacilli
    • facultative anaerobes
    • non-spore forming
    • possess fimbriae and flagella
    • pathogenic
    • antibiotic resistance
    • genetic plasticity
  • Different toxins produced by Enterobacters
    • hemolysin
    • cytotoxins
    • endotoxins
    • enterotoxins
    • siderophores
    • extracellular enzymes
    • antiphagocytic capsule
  • Citrate utilization
    • to differentiate GNB of Enterobacteriaceae
    • also called Simmon's citrate test
  • Simmon's citrate agar - contains citrate as main source of energy in the citrate utilization
  • Citrase - breaks down citrate into oxoloacetate and acetate, where oxoloacetate is further broken down to form pyruvate and carbon dioxide
  • Positive citrate test - shift in pH level and change in color
  • Methyl red test
    • detects the production of sufficient acid during fermentation of glucose
    • pH of an old culture is sustained below a value of about 4.5
  • In Enterobacters, glucose is converted to pyruvic acid and further metabolized to produce stable acid (lactic acid, acetic acid, formic acid)
  • Positive MR test - the color of methyl red changes from yellow to red
  • Voges - proskauer test
    • used to determine if an organism produces acetylmethyl carbinol from glucose fermentation
    • if present, it is converted into diacetyl in the presence of alpha napthol
  • The diacetyl and quanidine-containing compounds are then condensed to from a pinking red polymer.
  • K - Alkaline, red
    A - Acidic, yellow