Liofilchem® Barnes Agar Base

Liofilchem® Barnes Agar Base is a selective basal medium specifically formulated for the isolation and presumptive identification of fecal streptococci. This medium is highly effective in differentiating various group D streptococci and supports selective growth while inhibiting other bacterial contaminants. The incorporation of Triphenyl-tetrazolium Chloride (TTC) enhances the visualization of colonies through color differentiation.

Composition:

The medium contains the following components (per liter):

• Tryptone: 10.0 g (Provides nitrogen, amino acids, and essential nutrients for bacterial growth)
• Yeast Extract: 10.0 g (Supplies B-group vitamins and other growth factors)
• Thallium Acetate: 1.0 g (Selective agent to inhibit Gram-positive bacteria, excluding group D streptococci)
• Dextrose Anhydrous: 10.0 g (Fermentable carbohydrate providing energy)
• Agar: 14.0 g (Solidifying agent)
• Final pH: 6.0 ± 0.2 at 25°C

Key Features:

1. Selective Properties: Thallium acetate ensures selective growth of fecal streptococci by inhibiting Gram-positive bacteria not belonging to group D.
2. Differentiation of Streptococci: The addition of TTC allows visualization of group D streptococci colonies with distinctive color patterns.
3. Broad Applications: Suitable for clinical, food, and environmental microbiology to isolate and identify fecal contamination.
4. Ease of Preparation: No complex preparation steps, ensuring easy and consistent use in the laboratory.

Applications:

• Clinical Microbiology:
  • Identification of group D streptococci in clinical samples for presumptive diagnosis.
• Food Safety:
  • Detection and quantification of fecal streptococci in food products, ensuring compliance with safety regulations.
• Environmental Testing:
  • Monitoring water quality and detecting fecal contamination in wastewater and surface water.

Preparation Instructions:

1. Rehydration:
   • Suspend 45.0 g of powder in 990 ml of distilled or deionized water.
   • Heat and gently agitate until the medium is completely dissolved.
2. Sterilization:
   • Autoclave at 118°C for 15 minutes.
3. Supplementation:
   • Cool the sterilized medium to 45-50°C.
   • Aseptically add 10 ml of TTC 1% supplement (Catalog Code: 80300) and mix thoroughly.
4. Dispensing:
   • Dispense the prepared medium into sterile Petri dishes.

Test Procedure:

1. Inoculation:
   • Apply the sample, either undiluted or diluted, directly to the surface of the prepared plates.
2. Incubation:
   • Incubate the plates at 36 ± 1°C for 24 hours in an aerobic atmosphere.
3. Observation:
   • Observe the colony morphology:
     • White or light pink colonies: Enterococcus faecium and Enterococcus bovis.
     • Dark red-centered colonies with a white ring: Enterococcus faecalis.
     • Uniformly red colonies: Streptococcus lactis and other group N species.

Results Interpretation:

• Examine colonies for growth and distinctive coloration patterns as described above.
• For confirmation, perform additional biochemical or serological tests to identify specific streptococci species.

Quality Control:

• Dehydrated Medium:
  • Appearance: Homogeneous, light beige powder.
• Prepared Medium:
  • Appearance: Clear, light amber.
• Expected Microbial Results:
  • Enterococcus faecalis ATCC 19433: Good growth with red colonies.
  • Escherichia coli ATCC 25922: Inhibited.
  • Streptococcus pyogenes ATCC 19615: Inhibited.
  • Staphylococcus aureus ATCC 25923: Inhibited.

Storage and Shelf Life:

• Dehydrated Medium:
  • Store at 10-30°C, away from light, in the original tightly sealed container.
  • Valid for 2 years from the date of manufacture.
• Prepared Medium:
  • Store at 2-8°C, protected from light.
  • Do not use the product beyond the expiry date or if there are signs of contamination or deterioration.

Performance and Limitations:

• Some strains of streptococci may require additional tests for definitive identification.
• Colony morphology can vary slightly between strains; use supplemental tests for confirmation.
• Overheating during preparation may reduce medium performance.

Safety Information:

• Designed for in vitro diagnostic use.
• Not classified as hazardous under current regulations.
• Operators must be trained in microbiological techniques.
• Follow local regulations for waste disposal.

Presentation:

• Dehydrated Medium:
  • 500 g (Catalog Code: 610156)

References:

1. Barnes, E. M. (1956). "Methods for the isolation of fecal streptococci from bacon factories." J. Appl. Bacteriol. 19:193-203.
2. Barnes, E. M. (1956). "Tetrazolium reduction as a means of differentiating Streptococcus faecalis from Streptococcus faecium." J. Gen. Microbiol. 14:57-68.
3. ICMSF. (1978). "Microorganisms in foods 1: Their significance and methods of enumeration." 2nd ed.