Biochemical Activities of Microorganisms

• What are the three sugars used in TSI agar

  glucose

  sucrose

  lactose
• Triple Sugar Iron Agar

  • a differential medium used to determine carbohydrate fermentation and H2S production
  • prepared as a slant
• What pH indicator is used for TSI agar?

  phenol red
• Indicator for H2S production in TSI agar: black precipitate
• [TSI interpretation]

  Red/Yellow

  K/A

  glucose fermentation, peptone catabolized
• [TSI interpretation]

  Yellow/Yellow

  A/A

  glucose and lactose and/or sucrose fermentation
• [TSI interpretation]

  Red/Red

  K/K

  no fermentation

  peptone catabolized
• happens when all the glucose is consumed but the bacteria cannot utilize lactose and/or sucrose as energy source


  peptone catabolism
• Peptone catabolism causes the release of ammonia, making the pH more alkaline
• [TSI]

  Bacteria that can utilize peptones aerobically and anaerobically will make the tube (_/_)

  K/K
• [TSI]

  Bacteria that can only use peptones aerobically will make the tube (_/_)

  K/NC
• Sulfide Indole Motility Agar

  • used to test for indole production, motility, and H2S production
• [SIM]

  Indole test screens for the ability of an organism to degrade the amino acid tryptophan and produce indole
• [SIM]

  Production of indole reaction mechanism:

  tryptophan + water = indole + pyruvic acid + ammonia
• Positive for motility: reversed pine-tree projections

  Negative for motility: bacteria grow along the stab line only
• SIM agar is more sensitive than TSI in detecting H2S production.
• Indole production is indicated by the development of a purple-red color in the reagent layer of the medium.
• Nitrate reduction indicates a facilitation of anaerobic metabolism.