Selenite Cystine Broth Base is a modified enrichment medium used for the selective isolation of Salmonella spp. from fecal samples, food products, and other materials. It is based on Leifson's formula, enhanced with the addition of L-cystine, which helps reduce the toxicity of selenite, making it more efficient for Salmonella isolation while limiting the growth of competing organisms.
Key Features
- Selective Enrichment:
- Designed to inhibit non-target organisms while promoting the growth of Salmonella.
- Meets the requirements of the AOAC, APHA, and USP for Salmonella detection.
- Enhanced Formula:
- The addition of L-cystine reduces selenite's toxicity to microorganisms, providing a balanced selective medium.
- Broad Applications:
- Suitable for testing feces, foodstuffs, dairy products, and environmental samples.
- Recommended for food safety and clinical diagnostic laboratories.
Typical Composition (g/L)
Component | Amount (g/L) | Function |
---|
Tryptone | 5.0 | Provides essential nitrogen for microbial growth. |
Lactose | 4.0 | Fermentable carbohydrate to stabilize pH. |
Disodium Phosphate | 10.0 | Buffer to maintain pH stability. |
L-Cystine | 0.01 | Reduces selenite toxicity and aids in microbial growth. |
pH | 7.0 ± 0.2 @ 25°C | Optimized for Salmonella enrichment. |
Preparation Instructions
- Sodium Biselenite Solution:
- Dissolve 4 g of sodium biselenite (LP0121) in 1 L of distilled water.
- Broth Base:
- Add 19 g of Selenite Cystine Broth Base to the sodium biselenite solution.
- Warm gently to dissolve and mix thoroughly.
- Sterilization:
- Sterilize in free-flowing steam for 15 minutes.
- DO NOT AUTOCLAVE, as selenite may degrade under high pressure and temperature.
Applications
- Clinical Microbiology:
- Enrichment of Salmonella spp. from fecal samples in diagnostic testing.
- Food Safety Testing:
- Detection of Salmonella spp. in food products, including dairy and processed foods.
- Environmental Testing:
- Recovery of Salmonella spp. from environmental samples like sewage and water.
Technique and Usage
- Sample Inoculation:
- Add 1-2 g of solid sample to 10-15 mL of the medium.
- For liquid samples, use double-strength broth and mix in a 1:1 ratio.
- Incubation:
- Incubate at 35-37°C for 12-24 hours.
- For some samples, incubation at 43°C may enhance selectivity.
- Subculture:
- Transfer to selective agar plates, such as MacConkey or XLD agar, for further isolation and identification.
Storage and Stability
- Dehydrated Medium:
- Store at 10-30°C in a sealed, dry container.
- Prepared Medium:
- Store at 2-8°C, protected from light.
- Use before the expiry date on the label.
Appearance
State | Description |
---|
Dehydrated Medium | Straw-colored, free-flowing powder. |
Prepared Medium | Light straw-colored solution. |
Quality Control
Control Type | Organism | Expected Results |
---|
Positive Control | Salmonella Typhimurium ATCC® 14028 | Good growth. |
Negative Control | Escherichia coli ATCC® 25922 | Inhibited or no growth. |
Precautions
- Toxicity of Sodium Biselenite:
- Handle with care; toxic by inhalation or ingestion.
- Follow safety protocols and use personal protective equipment.
- Prepared Medium Stability:
- Discard if red precipitate (reduced selenite) forms at the bottom.
- Incubation Guidelines:
- Do not incubate longer than 24 hours, as selenite's selective effect diminishes after 6-12 hours.
Advantages
- Improved Selectivity:
- L-cystine minimizes toxicity, improving recovery rates for Salmonella spp.
- Compliant with Standards:
- Approved by AOAC, APHA, and USP for Salmonella testing.
- Versatile Applications:
- Suitable for a variety of sample types and testing workflows.
Applications Summary
- Clinical Diagnostics: Enriches and isolates Salmonella spp. from patient samples.
- Food Safety: Detects Salmonella spp. contamination in food and dairy products.
- Environmental Testing: Monitors Salmonella spp. in water and other environmental samples.
Selenite Cystine Broth Base is a reliable and effective tool for laboratories focused on food safety, clinical diagnostics, and environmental microbiology. Let me know if you need further details or related resources!
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