Lysine Iron Agar was originally designed by Edwards and Fife for the examination of colonies which blackened bismuth sulfite agar. Both Arizona and Salmonella blacken bismuth sulfite; however, some strains of Arizona actively ferment lactose which in turn suppresses the production of H2S in triple sugar iron agar. Lysine Iron Agar was designed to eliminate this problem. The incorporation of lysine is important since most species of both Salmonella and Arizona produce lysine decarboxylase. The authors reported that organisms which produce lysine decarboxylase raise the pH of the medium. Lysine Iron Agar is useful in detecting members of the Proteus and Providencia groups as these organisms produce a distinct red slant over an alkaline butt. This medium is not intended to replace or be a substitute for triple sugar iron agar. Sodium thiosulfate is the source of hydrogen sulfide and the ferric salt is the indicator. The carbohydrate dextrose is incorporated in the medium in a 0.1% concentration. All Gram negative enteric bacilli uniformly ferment dextrose. Some enteric organisms are capable of producing gas from dextrose. Gas production is shown by bubbles or breaks in the medium. Lysine Iron Agar is a differential medium used to detect the production of hydrogen sulfide and lysine decarboxylase by the Enterobacteriaceae. (Alpha Biosciences # L12-113-500gm)
Use: Lysine Iron Agar is a differential medium used to detect the production of hydrogen sulfide and lysine decarboxylase by the Enterobacteriaceae
Description: Lysine Iron Agar was originally designed by Edwards and Fife for the examination of colonies which blackened bismuth sulfite agar. Both Arizona and Salmonella blacken bismuth sulfite; however, some strains of Arizona actively ferment lactose which in turn suppresses the production of H2S in triple sugar iron agar. Lysine Iron Agar was designed to eliminate this problem. The incorporation of lysine is important since most species of both Salmonella and Arizona produce lysine decarboxylase. The authors reported that organisms which produce lysine decarboxylase raise the pH of the medium. Lysine Iron Agar is useful in detecting members of the Proteus and Providencia groups as these organisms produce a distinct red slant over an alkaline butt. This medium is not intended to replace or be a substitute for triple sugar iron agar. Sodium thiosulfate is the source of hydrogen sulfide and the ferric salt is the indicator. The carbohydrate dextrose is incorporated in the medium in a 0.1% concentration. All Gram negative enteric bacilli uniformly ferment dextrose. Some enteric organisms are capable of producing gas from dextrose. Gas production is shown by bubbles or breaks in the medium.
Formula* per Liter:
- Pancreatic Digest of Gelatin..........10.0g
- Dextrose ........................................ 1.0g
- Yeast Extract .................................... 3.0g
- Sodium Thiosulfate ..................... 0.04g
- L-Lysine ............................................. 10g
- Ferric Ammonium Citrate ............. 0.5g
- Bromocresol Purple ...................... 0.02g
- Agar .............................................. 13.5g
Final pH: 6.7 ± 0.2 at 25.0°C
* Grams per liter may be adj. or formula supplemented to obtain desired performance
Preparation: Mix 33 grams of the medium in one Liter of purified water until evenly dispersed. Heat with repeated stirring and boil for one minute to dissolve completely. Distribute into test tubes and autoclave for 15 minutes at 121.0°C. After autoclaving, slant tubes to prepare deep butts.
Quality Control Specifications:
- The powder is homogeneous, free flowing and light reddish beige.
- Visually the prepared medium is clear to slightly hazy and reddish purple.
- Expected cultural response after 18-48 hours at 35.0°C.
Organism                                                                         Result (Slant/Butt/H2S)
Citrobacter freundii ATCC 8090Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â K/A/+
Escherichia coli ATCC 25922Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â K/K/-
Proteus mirabilis ATCC 12453Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â R/A/-
Salmonella typhimurium ATCC 14028Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â K/K/+
Key: K = Alkaline, A = Acid, R = Oxidative deamination
Storage: Store the sealed bottle containing the dehydrated medium at 2 to 30.0°C. Once opened and recapped, place the container in a low humidity environment at the same storage temperature. Protect it from moisture and light. The dehydrated medium should be discarded if it is not free flowing or if the color has changed from the original light reddish beige color.
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