Negative and Positive

• Sugar Fermentation


  Positive: Pinkish-red (acidic)

  Negative: Yellow to colorless (alkaline)
• Mineral Oil


  Closed for anaerobic environment
• Sugar Fermentation


  Fermentative: Closed oxidative & there is change in color

  Oxidative: Opened test tube fermentative & there is change in color in the no mineral oil
• Indole Production


  Positive: Red ring

  Negative: Yellow Ring
• Methyl Red (MR Test)


  MR +:Bright red color

  MR -: Yellow color
• Voges-Proskauer (VP) Test


  Positive: Pink color in 2-5mins, Crimson red in 30mins

  Negative: Remains yellow or colorless for 30mins
• Citrate Utilization


  • Simmons' Citrate Medium
  • Koser's Citrate Medium
• Simmons' Citrate Medium


  Positive: Blue color and streak of growth

  Negative: Original green color and no growth
• Koser's Citrate Medium


  Positive: Turbidity

  Negative: No turbidity
• Nitrate Reduction Test


  Positive: Red color

  Negative: No color development
• Urease Test


  Positive: Purple-pink

  Negative: Pale yellow
• Catalase Production


  Positive: Immediate bubbling

  Negative: No bubbling
• Oxidase Test Methods


  • Plate Method
  • Dry Filter Paper Method
  • Wet Filter Paper Method
• Oxidase Test


  Positive: Deep purple within 10sec

  Negative: No reaction
• Phenylalanine Deaminase Test


  Positive: Green

  Negative: No color change
• Hydrogen Sulfide Production


  Positive: Black

  Negative: No color change
• Potassium Cyanide Test


  Positive: Turbidity due to growth

  Negative: Clear, no growth
• Triple Sugar Iron (TSI) Agar

  Red color (alkaline): no fermentation

  Yellow (acidic): fermentation of carbohydrate

  Bubbles in the butt: gas is produced during fermentation of carbohydrate

  Blackening of the medium: H2S (Hydrogen Sulfide) production
• TSI Agar


  • Red/Red: No fermentation of glucose, lactose or sucrose
  • Red/Yellow: Glucose fermented; lactose or sucrose not fermented
  • Red/Yellow/H2S: Glucose fermented; lactose not fermented, H2S produced
  • Yellow/Yellow: Glucose and lactose/sucrose fermented