Description
Listeria Chromogenic Medium: Rapid Detection of Listeria monocytogenes
In the food and medical industries, Listeria Chromogenic Medium plays a crucial role in the rapid detection of Listeria monocytogenes, a significant pathogen linked to foodborne illnesses. This innovative medium enables laboratories to identify Listeria strains efficiently, often within three days. When cultured, colonies of Listeria monocytogenes appear blue and are surrounded by an opaque ring, making them easily distinguishable from other organisms.
Key Features and Composition
The formulation of Listeria Chromogenic Medium includes essential ingredients that support optimal growth conditions. Below is a breakdown of the components for each 1-liter preparation:
| Ingredient | Quantity |
|---|---|
| Peptone | 70.0 g |
| Chromogenic Reagent | 1.0 g |
| Sodium Chloride | – |
| Lithium Chloride | – |
| Bacteriostatic Agents | – |
Peptone provides nitrogen and amino acids necessary for bacterial growth. The chromogenic reagent facilitates the color change indicative of Listeria monocytogenes. Moreover, sodium chloride maintains osmotic pressure, while lithium chloride inhibits unwanted Gram-negative bacteria.
The final pH is adjusted to 7.2 ± 0.2 at 25℃, ensuring ideal conditions for microbial activity.
Preparation and Usage
To prepare this medium, begin by suspending 14.2 g of the dehydrated powder in 180 ml of distilled water. Then, add the Listeria additive and bacteriostatic agents as specified. After autoclaving, allow the medium to cool to around 50℃ before pouring into sterile petri dishes with a thickness of about 5 mm. This thickness helps in observing the opaque ring.
Steps for Culturing
- Prepare your sample solution according to national standards, such as SN or FDA guidelines.
- Inoculate samples into Listeria enrichment broths or Half-Fraser broths at a mixing ratio of 1:10, incubating at 30℃ for 24 hours.
- Transfer one loop of the enrichment broth onto the Listeria Chromogenic Medium and incubate at 37℃ for 24-48 hours.
Quality Control and Performance
Quality control remains fundamental in laboratory settings. The dehydrated powder should be homogeneous and flowable, while the prepared medium appears as an opaque milky white solid. Testing with reference strains such as Listeria monocytogenes ATCC27853 confirms growth with characteristic blue colonies and opaque rings.
Sensitivity Testing
The following table summarizes the growth results for various strains:
| Strain | Appearance | Growth |
|---|---|---|
| Listeria monocytogenes | Blue colonies with opaque rings | +++ growth |
| Listeria innocua | Blue colonies with opaque rings | +++ growth |
| Listeria seeligeri | Blue colonies without opaque rings | +++ growth |
| Staphylococcus aureus | Yellow colonies | ++ growth |
| E. coli and Salmonella | No growth | – |
Storage Recommendations
For optimal results, store prepared plates at 2-8℃, away from direct light. Additionally, keep the dehydrated powder in a dark, dry place to maintain its effectiveness. Proper storage ensures the longevity and reliability of the medium.
Conclusion
In summary, Listeria Chromogenic Medium stands as an indispensable tool for laboratories focused on food safety and clinical diagnostics. Its rapid detection capabilities, combined with clear visual indicators, streamline the identification of Listeria monocytogenes. By investing in Listeria Chromogenic Medium, laboratories can enhance testing efficiency and accuracy in pathogen detection, thereby ensuring that food products are safe for consumption. Ultimately, this medium supports high safety standards and compliance with regulations in both commercial kitchens and clinical labs.
visit our [Chromogenic Medium Series] for more related products
Reviews
There are no reviews yet.