Liofilchem® Mannitol Salt Agar

Liofilchem® Mannitol Salt Agar (MSA) is a selective and differential microbiological medium designed for the isolation and enumeration of staphylococci, particularly pathogenic Staphylococcus aureus. Its high salt concentration and mannitol fermentation properties make it suitable for distinguishing mannitol-fermenting staphylococci from non-fermenting strains. The medium adheres to harmonized USP/EP/JP standards, making it suitable for pharmaceutical, clinical, and food microbiology applications.

Key Features

1. Selective and Differential Medium:
   • Contains 7.5% sodium chloride, which inhibits most organisms except staphylococci.
   • Differentiates mannitol-fermenting staphylococci (e.g., S. aureus) by a characteristic yellow zone around colonies.
2. Versatile Application:
   • Suitable for clinical samples, food testing, and non-sterile product testing.
   • Complies with harmonized USP/EP/JP methods for detecting S. aureus.
3. Reliable Results:
   • Produces yellow colonies with yellow zones for S. aureus, while coagulase-negative staphylococci form red or colorless colonies.
4. Long Shelf Life:
   • Dehydrated medium: 4 years.
   • Ready-to-use plates: 6 months.
5. Multiple Formats:
   • Available as dehydrated media, ready-to-use plates, and pre-prepared bottles for various laboratory needs.

Typical Formula

Applications

1. Clinical Microbiology:
   • Isolates pathogenic staphylococci from clinical specimens, including wound exudates and respiratory samples.
2. Food Safety Testing:
   • Detects and enumerates S. aureus in food samples and other materials of sanitary importance.
3. Pharmaceutical Microbiology:
   • Suitable for testing non-sterile pharmaceutical products as per harmonized methods.
4. Environmental Monitoring:
   • Used for isolating S. aureus from environmental samples in food and pharmaceutical industries.

Preparation Instructions

1. Dehydrated Medium:
   • Suspend 111 g of powder in 1 liter of distilled or deionized water.
   • Heat to boiling, shaking frequently until fully dissolved.
   • Sterilize in an autoclave at 121°C for 15 minutes.
2. Ready-to-Use Bottles:
   • Melt medium in a water bath at 100°C, with the cap partially loosened.
   • Mix well and distribute aseptically into sterile Petri dishes.

Test Procedure

1. Ensure the plates are free of visible moisture before use.
2. Inoculation:
   • Streak the specimen directly onto the agar surface or spread a sample from an enrichment culture.
3. Incubation:
   • Incubate plates aerobically at 35 ± 2°C for 24-48 hours.

Interpreting Results

• Staphylococcus aureus:
  • Yellow or white colonies surrounded by a yellow zone due to mannitol fermentation.
• Coagulase-Negative Staphylococci:
  • Small, colorless to red colonies without a color change in the medium.
• Other Bacteria:
  • Inhibited by the high salt concentration.

Suspected S. aureus colonies should be confirmed using additional identification tests, such as coagulase activity testing on Baird Parker RPF Agar.

Storage and Stability

• Dehydrated Medium: Store at 10-30°C in a dry, tightly closed container.
• Prepared Media: Store at 10-25°C, away from light.
• Avoid moisture or contamination during storage.

Quality Control

Advantages

1. High Specificity:
   • Selectively isolates staphylococci while inhibiting other organisms.
2. Ease of Interpretation:
   • Differentiates S. aureus from other staphylococcal species through color changes.
3. Broad Utility:
   • Suitable for a variety of sample types, including clinical, food, and environmental samples.
4. Customizable:
   • Available in multiple formats to meet specific laboratory requirements.

Available Formats

Liofilchem® Mannitol Salt Agar (MSA) is an essential medium for microbiologists seeking reliable isolation and differentiation of staphylococcal species, particularly S. aureus. Its high salt concentration and mannitol fermentation properties make it highly specific, while its compliance with USP/EP/JP standards ensures reliability across various applications. This versatile medium is available in formats suitable for both small and large-scale laboratory operations.