Kligleir iron agar test microbiology

The Kligler Iron Agar (KIA) test is a biochemical test used to identify bacteria based on their ability to ferment glucose and lactose and to produce hydrogen sulfide (H₂S).

It is particularly useful for distinguishing among members of the family Enterobacteriaceae. Here’s an overview:


Principle of Kligleir iron agar test

  1. Carbohydrate Fermentation:
    • The medium contains glucose and lactose as fermentable carbohydrates.
    • Phenol red is used as a pH indicator:
      • Yellow: Acid production (fermentation).
      • Red: Alkaline conditions (no fermentation).
  2. If the organism produces gas during carbohydrate fermentation, gas bubbles or cracks in the agar may be observed.
  3. The medium contains sodium thiosulfate and ferric ammonium citrate, which react with H₂S to produce a black precipitate.
  4. Aerobic and Anaerobic Zones:
    • The slant portion represents aerobic conditions.
    • The butt portion represents anaerobic conditions.

Preparation of KIA Medium

Media Contains peptone, glucose (0.1%), lactose (1%), ferric ammonium citrate, sodium thiosulfate, phenol red, and agar.

Kligleir iron agar test Procedure

  1. Inoculate the KIA slant with a pure bacterial culture:
    • Streak the slant surface.
    • Stab the butt with the needle.
  2. Incubate at 35–37°C for 18–24 hours.

Interpretation of Results

  1. Slant/Butt Color Changes:
    • Red/Red (K/K): No fermentation (alkaline slant and butt).
    • Red/Yellow (K/A): Glucose fermentation only (alkaline slant, acid butt).
    • Yellow/Yellow (A/A): Both glucose and lactose fermentation (acid slant and butt).
  2. Gas Production:
    • Presence of bubbles or cracks indicates gas production.
  3. H₂S Production:
    • Black precipitate in the butt indicates hydrogen sulfide production.

Applications

  • Commonly used for distinguishing Escherichia coli, Salmonella spp., Shigella spp., and Klebsiella spp.
  • Particularly useful for identifying potential enteric pathogens.

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