Ready-to-use media
XLD Agar (Xylose Lysine Desoxycholate Agar) ISO
Medium for isolation of enteropathogenic species, especially Shigella and Salmonella in food and animal feeding stuffs, according to ISO Standards.
- Cat. No.
- LC-847
- Category
- Ready-to-use media
- Format
- 20 plates, 90 mm
- ISO 17025 quality control
- Yes
- Storage
- 2 to 14 °C
- Minimum guaranteed shelf life
- 1 month
- Standards
- ISO 19250ISO 21567ISO 6579
- Also available
- Ready-to-use medium, 1 format (LC-930)
- Also available
- Dehydrated medium, 1 format (LC-1080)
- Also available
- Dehydrated medium, 1 format (LC-1274)
Xylose Lysine Deoxycholate Agar is a selective differential medium, suitable for the detection of pathogenic enterobacteria in food, especially Shigella. A modification in the original formulation of Taylor allows the medium to perform to the specifications of the ISO standards. Gram-positive microbiota are inhibited by the low amount of deoxycholate, whilst Shigella grows.
Key features
Applications
Detection and selective isolation of Salmonella.
Industry
Food, water.
Standards
ISO 19250, ISO 21567, ISO 6579.
Presentation
20 prepared plates, 90 mm, with 21 ± 2 mL.
Description and technique
Xylose, lactose or sucrose fermentation produces acidification of the medium, which is shown by the indicator surrounding the colonies turning yellow. This colour disappears after 24 hours, so readings must be carried out between 18 and 24 hours.
Sulfide production from thiosulfate is easily detected because colonies become darker, due to the ferric sulfide precipitate. Lysine decarboxylation to cadaverine may also be observed in the medium, since it produces alkalinization and consequently the indicator turns red.
All these reactions allow a good differentiation of Shigella, which, other than Edwardsiella and Proteus inconstans, are the only enterobacteria that do not ferment xylose and therefore show a negative fermentation reaction. Salmonella does ferment xylose, but it is consumed quickly and the medium becomes alkaline due to lysine decarboxylation, which may hide the reaction. The difference between Shigella and Salmonella is that the latter colonies become darker due to ferrous sulfide precipitates, which is also a common characteristic of Edwardsiella. Other types of enterobacteria do not suffer this phenomenon, since acid accumulation due to lactose and sucrose fermentation is so great that it prevents pH reversion by decarboxylation and even ferrous sulfide precipitate in the first 24 hours.
The typical colonial appearances of Enterobacteriaceae after 24 ± 3 h of incubation at 37 °C appear in the quality control.
Presentation
| Presentation | 20 prepared plates, 90 mm |
|---|---|
| Filling | 21 ± 2 mL |
| Packaging | 1 box with 2 cellophane bags with 10 plates/bag. |
Composition
| Ingredient | g/L |
|---|---|
| Xylose | 3.750 |
| L-Lysine | 5.000 |
| Lactose | 7.500 |
| Sucrose | 7.500 |
| Sodium chloride | 5.000 |
| Yeast extract | 3.000 |
| Phenol red | 0.080 |
| Sodium deoxycholate | 1.000 |
| Sodium thiosulfate | 6.800 |
| Ammonium ferric citrate | 0.800 |
| Agar | 15.000 |
Quality control
Physical/chemical control
| Color | Red |
|---|---|
| pH | 7.4 ± 0.2 at 25 °C |
Microbiological control
Spiral spreading: practical range 100 ± 20 CFU; min. 50 CFU (productivity) / 10⁴-10⁶ CFU (selectivity).
Microbiological control according to ISO 11133:2014/Amd 1:2018.
Aerobiosis. Incubation at 37 ± 1 °C, reading after 24 ± 3 h.
| Microorganism | Growth |
|---|---|
| Enterococcus faecalisATCC 29212, WDCM 00087 | Inhibited |
| Salmonella typhimuriumATCC 14028, WDCM 00031 | Good - culture medium and red colonies, black center (H₂S +) |
| Salmonella entericaATCC 13076, WDCM 00030 | Good - culture medium and red colonies, black center (H₂S +) |
| Escherichia coliATCC 25922, WDCM 00013 | Partial inhibition |
Sterility control
Incubation 48 hours at 30-35 °C and 48 hours at 20-25 °C: NO GROWTH.
Check at 7 days after incubation in same conditions.
Bibliography
- ATLAS, R.M., L.C. PARK (1993) Handbook of Microbiological Media for the examination of Food. CRC Press Inc. Boca Raton.
- DOWNES, F.P. & K. ITO (2001) Compendium of Methods for the Microbiological Examination of Foods. 4th ed. APHA. Washington DC. USA.
- HORWITZ, W. (2000) Official Methods of Analysis of the AOAC International. 17th ed. Gaithersburg. MD. USA.
- ICMSF (1978) Microorganisms in Foods 1. University of Toronto Press.
- ISO Standard 6579-1 (2017) Microbiology of food chain - Horizontal method for the detection, enumeration and serotyping of Salmonella - Part 1: Detection of Salmonella spp.
- ISO 11133:2014/Amd 1:2018. Microbiology of food, animal feed and water. Preparation, production, storage and performance testing of culture media.
- ISO 21567 Standard (2004) Microbiology of food and animal feeding stuffs - Horizontal method for the detection of Shigella spp.
- PASCUAL ANDERSON, Mª R. (1992) Microbiología Alimentaria. Díaz de Santos, S.A. Madrid.
- TAYLOR, W.J. (1965) Isolation of Shigella. I. Xylose Lysine Agars: New media for isolation of enteric pathogens. Am. J. Clin. Path 44:471-475.
- US FDA (Food and Drug Administration) (1998) Bacteriological Analytical Manual 8th ed. AOAC International. Gaithersburg. MD. USA.
What you receive
The product
Shipped under controlled temperature when the product requires it.
Lot certificate
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Tracked shipment
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Frequently asked questions
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