Liofilchem® Cetrimide Agar (copy)

Cetrimide Agar is a selective medium specifically designed for the isolation and differentiation of Pseudomonas aeruginosa. It is widely used in clinical, pharmaceutical, industrial, and environmental microbiology to detect and identify this pathogen. The medium supports selective growth by inhibiting unwanted microbial species and enhances the production of specific pigments, including pyocyanin and pyoverdin, characteristic of Pseudomonas aeruginosa. It complies with the harmonized standards of the European, United States, and Japanese Pharmacopoeias.

Key Features and Components

Composition (Per Liter):

• Pancreatic Digest of Gelatin (20.0 g): Provides essential amino acids, nitrogen, carbon, vitamins, and minerals.
• Magnesium Chloride (1.4 g): Stimulates pigment production.
• Dipotassium Sulfate (10.0 g): Promotes production of water-soluble pigments like pyocyanin and pyoverdin.
• Cetrimide (0.3 g): Acts as a selective agent with bactericidal properties against Gram-positive bacteria and some Gram-negative species.
• Agar (13.6 g): Solidifying agent.
• Glycerol (10.0 ml): Serves as a carbon source.
• Final pH: 7.2 ± 0.2 at 25°C.

Applications

1. Clinical Microbiology:
   • Used to isolate P. aeruginosa from clinical specimens, including wound exudates, respiratory secretions, and other pathological materials.
   • Serves as an aid in diagnosing infections caused by P. aeruginosa.
2. Pharmaceutical and Industrial Testing:
   • Follows harmonized pharmacopoeial standards for microbiological testing of non-sterile products.
   • Ensures quality control in pharmaceutical manufacturing by detecting contaminants.
3. Environmental and Food Microbiology:
   • Applied for the detection of P. aeruginosa in water, environmental samples, and food production areas.

Test Methodology

Preparation:

1. Dehydrated Medium:
   • Suspend 46.7 g of the powder in 990 ml of deionized/distilled water.
   • Add 10 ml of Glycerol Supplement (provided separately).
   • Heat to boiling until completely dissolved.
   • Sterilize by autoclaving at 121°C for 15 minutes.
   • Cool to 45-50°C and pour into Petri dishes.
2. Ready-to-Use Medium:
   • Melt pre-prepared bottles in a water bath at 100°C.
   • Ensure homogeneity by gently mixing.
   • Pour into sterile plates under aseptic conditions.

Inoculation and Incubation:

• Direct Streaking: Inoculate the specimen directly onto the agar surface.
• Subculture: Transfer from enrichment broths like Tryptic Soy Broth for samples requiring pre-enrichment.
• Incubation Conditions:
  • Incubate aerobically at 32.5 ± 2.5°C.
  • Duration: 18-72 hours (based on specimen type and microbial load).

Interpretation of Results

1. Positive for Pseudomonas aeruginosa:
   • Colonies exhibit a yellow-green to blue-green coloration.
   • Fluoresce under UV light due to the production of pigments such as pyocyanin and pyoverdin.
   • A positive oxidase reaction confirms the result.
2. Negative for Pseudomonas aeruginosa:
   • Absence of characteristic pigmentation.
   • Non-P. aeruginosa species (e.g., Klebsiella, Proteus) may grow but without the typical fluorescence or coloration.
3. Note: Some mucoid strains of P. aeruginosa may lack pigmentation or have a delayed oxidase reaction, requiring additional confirmatory tests.

Quality Control and Performance

Control Strains:

• Pseudomonas aeruginosa ATCC® 9027: Good growth; yellow-green to blue-green colonies.
• Escherichia coli ATCC® 8739: Inhibited growth.
• Staphylococcus aureus ATCC® 25923: Inhibited growth.

Expected Appearance:

• Dehydrated Medium: Free-flowing, homogeneous, light beige powder.
• Prepared Medium: Slightly opalescent, light amber with precipitates.

Shelf Life:

• Dehydrated Medium: 4 years.
• Prepared Plates: 6 months.

Advantages

1. Selective Growth: Cetrimide suppresses unwanted microbial species, allowing specific growth of P. aeruginosa.
2. Enhanced Detection: Stimulates pigment production for easier visual identification.
3. Pharmacopoeial Compliance: Meets USP, EP, and JP standards, ensuring global applicability.

Limitations

• False Negatives: Certain mucoid strains may not produce visible pigments, requiring further testing.
• Growth Requirements: Some P. aeruginosa strains may have unique substrate or temperature needs.
• Cross-Reactivity: Enteric organisms (e.g., Klebsiella) may slightly color the medium, though this is distinguishable from fluorescein.

Safety and Handling

1. Storage:
   • Dehydrated medium: Store at 10-30°C in a dry environment.
   • Prepared plates: Store at 10-25°C away from light.
2. Precautions:
   • Handle specimens as potentially infectious.
   • Dispose of waste as per institutional guidelines.

Ordering Information

• Dehydrated Media:
  • 100 g (Ref. 620041)
  • 500 g (Ref. 610041)
  • 5 kg (Ref. 6100415)
• Ready-to-Use Plates:
  • 90 mm plates (Ref. 10033)
• Glycerol Supplement:
  • 4 x 50 ml (Ref. 80021)

Liofilchem® Cetrimide Agar is a reliable and selective medium for isolating Pseudomonas aeruginosa in clinical, pharmaceutical, and industrial settings. Its compliance with global pharmacopoeial standards ensures its utility in diverse microbiological applications.