Ready-to-use media
XLD Agar EP/USP
Solid medium for the isolation of enteropathogenic species, especially Salmonella and Shigella, according to Pharmacopoeial Harmonised Method and ISO Standard.
- Cat. No.
- LC-794
- Category
- Ready-to-use media
- Format
- 20 plates, 90 mm
- Storage
- 15 to 25 °C
- Minimum guaranteed shelf life
- 1 month
- Standards
- European Pharmacopoeia
Xylose Lysine Deoxycholate Agar is a selective differential medium, suitable for the detection of pathogenic enterobacteria, especially Shigella. Gram-positive microbiota are inhibited by the low amount of deoxycholate, whilst Shigella grows.
Key features
Applications
Selective isolation of Salmonella and Shigella.
Industry
Clinical, final product quality control, food, pharmaceutical/veterinary.
Standards
European Pharmacopoeia.
Presentation
20 prepared plates, 90 mm, with 21 ± 2 mL.
Description and technique
Xylose, lactose or sucrose fermentation produces the acidification of the medium, and this is seen by the indicator turning yellow around the colonies. This colour disappears after 24 hours, so observations must be carried out between 18 and 24 hours.
Hydrogen 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. Edwardsiella and Proteus inconstans are the only enterobacteria other than Shigella which do not ferment xylose and therefore show a negative fermentation reaction. Salmonella ferments xylose, but it is consumed quickly and alkalinization of the medium due to lysine decarboxylation may mask the reaction. Salmonella colonies become darker due to ferrous sulfide precipitates, which is also a common property with Edwardsiella.
Other types of enterobacteria do not suffer this phenomenon, since acid accumulation due to lactose and sucrose fermentation is so high that it prevents pH reversion by decarboxylation and even ferrous sulfide precipitate in the first 24 hours.
In the quality control, typical colonial appearances on XLD medium after 18-48 hours of incubation at 30-35 °C are described.
Presentation
| Presentation | 20 prepared plates, 90 mm |
|---|---|
| Filling | 21 ± 2 mL |
| Packaging | 1 box with 2 packs of 10 plates/pack. Single BOPP film. With desiccant. Lateral labelling. |
Composition
| Ingredient | g/L |
|---|---|
| Xylose | 3.50 |
| L-Lysine HCl | 5.00 |
| Lactose | 7.50 |
| Sucrose | 7.50 |
| Sodium chloride | 5.00 |
| Yeast extract | 3.00 |
| Phenol red | 0.08 |
| Sodium deoxycholate | 2.50 |
| Sodium thiosulfate | 6.80 |
| Ammonium ferric citrate | 0.80 |
| Agar | 13.5 |
Quality control
Physical/chemical control
| Color | Red |
|---|---|
| pH | 7.4 ± 0.2 at 25 °C |
Microbiological control
According to USP and European Pharmacopoeia.
Inoculate with 10-100 CFU according to the harmonized Pharmacopoeias or with 100-1000 CFU for selectivity.
Analytical methodology according to ISO 11133:2014/Amd 1:2018; A2:2020.
Aerobiosis. Incubation at 30-35 °C. Reading at 18-24/48 h.
| Microorganism | Growth |
|---|---|
| Salmonella typhimuriumATCC 14028, WDCM 00031 | Good - culture medium and red colonies, black center (H₂S +) |
| Salmonella abonyNCTC 6017 | Good - culture medium and red colonies, black center (H₂S +) |
| Staphylococcus aureusATCC 6538, WDCM 00032 | Inhibited |
Sterility control
Incubation 48 h at 30-35 °C and 48 h 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.
- EUROPEAN PHARMACOPOEIA 11.0 (2023) 11th ed. § 2.6.13. Microbiological examination of non-sterile products: Test for specified microorganisms. Harmonised Method. EDQM. Council of Europe. Strasbourg.
- 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.
- 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. Rev. A. AOAC International. Gaithersburg, Md. USA.
- USP 33 - NF 28 (2011) <62> Microbiological examination of non-sterile products: Test for specified microorganisms. Harmonised Method. USP Corp. Inc. Rockville. MD. USA.
What you receive
The product
Shipped under controlled temperature when the product requires it.
Lot certificate
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