Vn
Dilution and enrichment buffer
Antibiotic disc dispenser
INTENDED USE
- TraceMedia™ XLD Agar is a culture medium used for the isolation of Salmonella and Shigella from pharmaceutical, food, and water samples.
PRINCIPLE
- TraceMedia™ XLD Agar was developed by Taylor to enhance the recovery of Salmonella and Shigella.
- Sodium desoxycholate is an inhibitory substance for Gram-positive bacteria.
- Xylose is fermented by most enteric pathogens, except Shigella, enabling the differentiation of Shigella from other bacterial species. After xylose is depleted, Salmonella decarboxylates lysine (via lysine decarboxylase) into cadaverine, raising the pH. Salmonella bacteria then appear similar to Shigella in an alkaline environment.
- The formed colonies appear red due to the presence of the pH indicator phenol red.
- The addition of lactose and sucrose to the medium allows enteric bacteria to decarboxylate lysine and produce excessive acid, causing the indicator to turn yellow, facilitating their differentiation.
- In the basic medium, H2S-producing substances reduce citrate, leading to the formation of black centers within colonies.
- XLD agar serves as both a selective and differential medium for Salmonella and Shigella. It contains yeast extract as a nutrient and vitamin source. Additionally, sodium deoxycholate is used as a selective agent, inhibiting Gram-positive bacteria. Xylose is incorporated into the medium as it is fermented by all enteric bacteria except Shigella, and this characteristic allows for the differentiation of Shigella species.
- Lysine is included to aid in distinguishing Salmonella from other non-pathogenic bacteria. In the absence of lysine, salmonellae will rapidly ferment xylose and cannot be differentiated from other species. After salmonellae deplete the supply of xylose, lysine is attacked via the enzyme lysine decarboxylase, leading to alkaline reversal, which precedes Shigella’s reaction.
- To prevent alkaline reversal by lysine-positive coliform bacteria, lactose and sucrose are added to produce an excess of acid. The breakdown of xylose, lactose, and sucrose into acid causes the phenol red indicator to turn from red to yellow. Bacteria that decarboxylate lysine to form cadaverine can be recognized by the presence of red color around the colony due to elevated pH. These reactions can occur simultaneously or sequentially, resulting in the pH indicator displaying various color morphologies or changing its color from yellow to red with extended incubation.
- To further enhance the differentiating capability of this formula, an H2S-indicator system, including sodium thiosulfate and ferric ammonium citrate, is included for the detection of hydrogen sulfide production, leading to the formation of colonies with black centers.
The relevant samples are directly inoculated onto the agar plates.
- If the agar plates have been refrigerated, allow them to warm up to room temperature before inoculating the samples.
- Inoculate the samples onto the agar plates.
- Incubate the plates in an aerobic condition at 35 – 37°C for 16 – 24 hours.
BacterLab checks the quality of each batch of products using standard ATCC strains:
| Microorganism Strain | Typical Colony Characteristics after 16-24 hours | Incubation result at 35-37°C |
| S. Flexneri ATCC 12022 | Good growth, red colonies with black centers | |
| E.coli ATCC 25922 | Good growth, yellow colonies |
Ingredients per 1 liter (Reference):
| Yeast extract | 3 g |
| L-Lysine | 5 g |
| Lactose | 7.5 g |
| Sucrose | 7.5 g |
| Xylose | 3.5 g |
| Sodium desoxycholate | 2.5 g |
| Sodium chloride | 5 g |
| Sodium thiosulfate | 6.8 g |
| Ferric ammonium citrate | 0.8 g |
| Phenol red | 80.0 mg |
| Bacteriological agar | 13.5 g |
| The pH of the complete medium at 25°C is 7.4 ± 0.2. | |
*Please note that this composition is for reference purposes. Additionally, Our company will prepare the components as required or according to the tender documents.
| Product name | Product code | Packing |
| TraceMedia™ XLD Agar | TM12422 | 10 plates/box |
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