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
- 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).
- If the organism produces gas during carbohydrate fermentation, gas bubbles or cracks in the agar may be observed.
- The medium contains sodium thiosulfate and ferric ammonium citrate, which react with H₂S to produce a black precipitate.
- 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
- Inoculate the KIA slant with a pure bacterial culture:
- Streak the slant surface.
- Stab the butt with the needle.
- Incubate at 35–37°C for 18–24 hours.
Interpretation of Results
- 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).
- Gas Production:
- Presence of bubbles or cracks indicates gas production.
- 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.