Dehydrated culture media
MAL Agar
Medium used for detection and isolation of Salmonella H₂S positive such as S. typhi and to distinguish positive and negative mannitol enterobacteria.
- Cat. No.
- LC-1573
- Category
- Dehydrated culture media
- Format
- 500 g
- Storage
- 2 to 25 °C
- Minimum guaranteed shelf life
- 15 months
MAL (mannitol-arabinose-lactose) Agar is a nutrition medium which is used for isolation and detection of H₂S-positive salmonella such as Salmonella typhi and to distinguish mannitol positive and negative species of the family Enterobacteriaceae.
Key features
Applications
Differentiation of enterobacteria.
Industry
Food, water.
Preparation
41.9 g in one liter of distilled water; boil for one minute, do not overheat, do not autoclave.
Principles and uses
MAL Agar was first introduced in the 1980s by Pataky, a biologist from Presov, the Slovak Republic. This medium improved and expanded conditions for the isolation and differentiation of enterobacteria that the widely used XLD Agar normally provides. This medium is relatively unknown internationally as it has not received broad coverage in professional publications.
MAL Agar is both a selective and differential medium using sodium deoxycholate as the selective agent and therefore inhibits Gram-positive microorganisms. The nutritional component of the medium is provided by yeast extract. Fermentable carbohydrates such as mannitol, D-arabinose and lactose are utilized by salmonella bacteria and when exhausted, they attack lysine through the enzyme lysine decarboxylase, with reversion to an alkaline pH which mimics the Shigella reaction. To prevent similar reversion by lysine positive coliforms, lactose and other carbohydrates were added to produce acid in excess. To increase the differentiating ability of the formulation, an H₂S indicator system, consisting of sodium thiosulfate and ferric ammonium citrate, is included for the visualization of the production of hydrogen sulfide, resulting in the formation of colonies with black centers. The nonpathogenic H₂S-producers do not decarboxylate lysine; therefore, the acid reaction produced by them prevents the blackening of the colonies after 18 to 24 h incubation. Phenol red is a pH change indicator. Characteristic of this medium is the combined biochemical results of mannitol positive, D-arabinose negative, lysine decarboxylase positive, H₂S positive and lactose positive/negative, which is typical for salmonellae but only anomalously found with other flora.
Technical specifications
| Solubility | Without residues |
|---|---|
| Appearance | Fine powder |
| Color of the dehydrated medium | Beige |
| Color of the prepared medium | Pinky-red |
| Final pH (25 °C) | 7.3 ± 0.2 |
| Amount per litre | 41.9 g |
| Storage | 2 to 25 °C |
Formula
| Ingredient | g/L |
|---|---|
| Bacteriological agar | 12.5 |
| D-arabinose | 1.5 |
| Ferric ammonium citrate | 0.8 |
| Lactose | 4 |
| L-Lysine | 5 |
| Mannitol | 4 |
| Phenol red | 0.1 |
| Sodium chloride | 5 |
| Sodium deoxycholate | 1.5 |
| Sodium thiosulfate | 4.5 |
| Yeast extract | 3 |
Typical formula in g/L, adjusted and/or supplemented as required to meet performance criteria.
Preparation and use
Preparation
Suspend 41.9 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. DO NOT OVERHEAT. DO NOT AUTOCLAVE. Dispense into appropriate containers.
Instructions for use
Inoculate and incubate at a temperature of 35 ± 2 °C for 18-24 hours.
Quality control
Microbiological test
Incubation conditions: 35 ± 2 °C / 18-24 h.
| Microorganism | Specification | Characteristic reaction |
|---|---|---|
| Salmonella enteritidisATCC 13076 | Good growth | Yellow, black centered colonies |
| Escherichia coliATCC 25922 | Partially inhibited | Yellow and opaque colonies |
| Proteus mirabilisATCC 25933 | Good growth | Translucent colonies without swarming |
Bibliography
- King, S. & Metzger. Appl. Microbiol. 16:577. 1968.
- King, S. & Metzger. Appl. Microbiol. 16:579, 1968.
- Isenberg, Kominos & Siegel. Appl. Microbiol. 18:656. 1969.
- Hoben, Aston & Peterson. Appl. Microbiol. 26:126. 1973.
- Polloch & Dalhgren. Appl. Microbiol. 27:197. 1974.
- Peloxv, Lavirotte & Pons. Microbia, Tomo I No. 1. 1975.
- Goo et al. Appl. Microbiol. 26:288, 1973.
What you receive
The product
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