Dehydrated culture media
Lysine Iron Agar
For studies of the decarboxylation of lysine for the rapid differentiation of Salmonella arizonae.
- Cat. No.
- LC-1044
- Category
- Dehydrated culture media
- Format
- 500 g
- Storage
- 2 to 25 °C
- Minimum guaranteed shelf life
- 15 months
- Also available
- Ready-to-use medium, 1 format (LC-4007)
Lysine Iron Agar is used for the rapid differentiation of Enterobacteriaceae, especially Salmonella arizonae, on the basis of lysine decarboxylation and deamination, and H₂S production. This medium is very useful for the rapid differentiation of Salmonella arizonae from Citrobacter and Proteus spp.
Key features
Applications
Differentiation of enterobacteria and Salmonella arizonae.
Industry
Food.
Preparation
33 g in one liter of distilled water; boil for one minute, sterilize in autoclave at 121 °C for 12 minutes.
Principles and uses
The strains that rapidly ferment the lactose produce a large quantity of acid, changing the original purple color of the medium to yellow. Some strains of S. arizonae can rapidly ferment lactose and form colonies that are colorless or pink to red on media such as MacConkey Agar (LC-1052) or Desoxycholate Agar (LC-1020). Lysine Iron Agar is especially formulated to avoid this confusion.
Gelatin peptone and Yeast extract provide the nutrient sources for growth: nitrogen, vitamins, minerals and amino acids.
One reaction is the degradation of the fermentable carbohydrate Dextrose, with the production of acid, manifested in the color change from red to yellow. Sodium thiosulfate provides Sulphur and Ferric ammonium citrate is the indicator for H₂S production under alkaline conditions. The bacteria that decarboxylate the L-Lysine to cadaverine, such as Salmonella arizonae, are identified by the presence of a purple-red color due to the elevation of the pH. Bromocresol purple is the pH indicator. Bacteriological agar is the solidifying agent.
Technical specifications
| Solubility | Without residues |
|---|---|
| Appearance | Fine powder |
| Color of the dehydrated medium | Beige |
| Color of the prepared medium | Purple |
| Final pH (25 °C) | 6.7 ± 0.2 |
| Amount per litre | 33 g |
| Storage | 2 to 25 °C |
Formula
| Ingredient | g/L |
|---|---|
| Bacteriological agar | 13.5 |
| Bromocresol purple | 0.02 |
| Dextrose | 1 |
| Ferric ammonium citrate | 0.5 |
| Gelatin peptone | 5 |
| L-Lysine | 10 |
| Sodium thiosulfate | 0.04 |
| Yeast extract | 3 |
Typical formula in g/L, adjusted and/or supplemented as required to meet performance criteria.
Preparation and use
Preparation
Suspend 33 grams of the medium in one liter of distilled water. Mix well and dissolve by heating with frequent agitation. Boil for one minute until complete dissolution. Dispense into tubes and sterilize in autoclave at 121 °C for 12 minutes. Allow to cool in a slanted position.
Instructions for use
Inoculate and incubate at 35 ± 2 °C for 18-48 hours.
Cultures rapidly producing lysine decarboxylase cause an alkaline reaction (purple colour) throughout the medium. Those organisms that do not decarboxylate lysine produce an alkaline slant and an acid butt (yellow colour). Proteus and Providencia produce a characteristic orange-red color on the slant while the butt is yellow from the production of acid from the deamination of lysine.
Quality control
Microbiological test
Incubation conditions: 35 ± 2 °C / 18-48 h.
| Microorganism | Specification | Characteristic reaction |
|---|---|---|
| Shigella flexneriATCC 12022 | Good growth | Red-purple slant, yellow butt, H₂S (-) |
| Salmonella arizonaeATCC 13314 | Good growth | Red-purple slant, red-purple butt, H₂S (+) |
| Salmonella typhimuriumATCC 14028 | Good growth | Red-purple slant, red-purple butt, H₂S (+) |
| Escherichia coliATCC 25922 | Good growth | Red-purple slant, red-purple butt, H₂S (-) |
| Proteus mirabilisATCC 25933 | Good growth | Deep red slant, yellow butt, H₂S (-) |
| Citrobacter freundiiATCC 8090 | Good growth | Red-purple slant, yellow butt, H₂S (+) |
Bibliography
- Edwards and Fite Applied Microbiol. 9:478, 1961.
- Edwards and Ewing. Identification of Enterobacteriaceae. Burgess Publishing Co. Minneapolis, Minn., 1962.
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