Liofilchem® Azide Maltose Agar KF

Liofilchem AZIDE MALTOSE AGAR KF is a selective microbiological medium specifically designed for the isolation and enumeration of fecal streptococci in water and food samples. This medium is widely recognized for its use in environmental and food microbiology testing, following guidelines recommended by organizations such as APHA, FDA, and ICMSF. It is also compliant with modern microbiological practices for detecting microbial contamination in various sample types.

Composition:

The medium contains the following components (per liter):

• Peptospecial: 10.0 g (Source of nitrogen and amino acids to support microbial growth)
• Yeast Extract: 10.0 g (Provides vitamins, particularly B-group, essential for microbial metabolism)
• Sodium Chloride: 5.0 g (Maintains osmotic balance)
• Sodium Glycerophosphate: 10.0 g (Acts as a buffering agent)
• Maltose: 20.0 g (Fermentable carbohydrate for energy)
• Lactose: 1.0 g (Additional fermentable sugar)
• Sodium Azide: 0.4 g (Selective agent inhibiting Gram-negative bacteria and certain other microbial groups)
• Brom Cresol Purple: 0.015 g (pH indicator for metabolic activity)
• Agar: 20.0 g (Solidifying agent)
• Final pH: 7.2 ± 0.2 at 25°C

Key Features:

1. Selective Inhibition: Sodium azide inhibits Gram-negative bacteria and streptococci not belonging to Group D, while allowing the selective growth of fecal streptococci.
2. TTC Indicator: When supplemented with TTC (Triphenyltetrazolium Chloride), the medium enables the visualization of fecal streptococci colonies as pink to red due to the reduction of TTC to triphenylformazan.
3. Versatile Application: Suitable for both water quality testing and food safety by employing membrane filtration or pour plate methods.
4. Broad Use: Recommended for various sample types including waters, foodstuffs, and environmental monitoring.
5. Ease of Preparation: The medium does not require sterilization by autoclaving, simplifying preparation and ensuring pH stability.

Applications:

1. Water Testing:
   • Monitoring microbial contamination in drinking water, surface water, and wastewater.
   • Adheres to standard methods for water quality assessment, such as ISO 7899-2.
2. Food Safety:
   • Isolation and enumeration of fecal streptococci in food samples to ensure compliance with food safety regulations.
3. Environmental Microbiology:
   • Detection of fecal contamination in environmental samples to monitor public health risks.
4. Membrane Filtration:
   • Used as part of the membrane filtration method for the concentration of microorganisms from large sample volumes.
5. Pour Plate Enumeration:
   • Quantitative assessment of microbial load in various sample types through direct plating.

Preparation Instructions:

1. Preparation of Dehydrated Medium:
   • Suspend 76.4 g of powder in 990 ml of distilled or deionized water.
   • Heat to boiling (~5 minutes) while stirring to dissolve completely. DO NOT STERILIZE.
   • Cool the medium to 45-50°C.
   • Aseptically add 10 ml of TTC 1% Supplement (Catalog Code: 80300) and mix well.
   • Dispense into Petri dishes and allow to solidify.
2. Storage:
   • Store the dehydrated medium at 10-30°C in a tightly sealed container to prevent moisture absorption.
   • Prepared plates should be stored at 2-8°C, protected from light.

Testing Procedures:

Pour Plate Method:

1. Dilute the test sample appropriately.
2. Place a selected volume of the sample into a sterile Petri dish.
3. Pour 15 ml of prepared medium (cooled to 45-50°C) into the dish and mix thoroughly.
4. Allow the agar to solidify and incubate at 36 ± 1°C for 48 hours.
5. Count pink to red colonies under low magnification.

Membrane Filtration Method:

1. Filter the sample using a sterile membrane filter (0.45 µm pore size).
2. Place the membrane on the surface of solidified medium in a Petri dish.
3. Incubate at 36 ± 1°C for 48 hours.
4. Count red or pink colonies, using magnification if needed.

Quality Control:

• Dehydrated Medium:
  • Appearance: Free-flowing, homogeneous, light-greenish beige.
• Prepared Medium:
  • Appearance: Very slightly opalescent, light purple.
• Expected Results:
  • Enterococcus faecalis: Good growth with red-centered colonies.
  • Escherichia coli: No growth or minimal growth.
  • Enterobacter aerogenes: Minimal to no growth.

Performance Characteristics:

• Adheres to ISO 7899-2 standards for fecal streptococci enumeration in water.
• Reliable selective properties due to sodium azide and TTC, ensuring specificity for fecal streptococci.
• Compatible with a wide range of testing methods, providing flexibility for laboratory workflows.

Storage and Shelf Life:

• Dehydrated Medium: 4 years at 10-30°C in a dry environment.
• Prepared Plates: Store at 2-8°C and use within the labeled expiry date.

Limitations:

• Some strains of Streptococcus bovis and Streptococcus equinus may be inhibited by sodium azide.
• Overheating during preparation can lower pH and reduce medium productivity.

Safety Information:

• Sodium azide is harmful by inhalation or ingestion and can react with metals to form explosive compounds. Handle with caution and consult the SDS for detailed safety practices.

Presentation:

• Dehydrated Medium:
  • 500 g (Catalog Code: 610154)
  • 100 g (Catalog Code: 620154)
• TTC 1% Supplement:
  • 10 test tubes (Catalog Code: 80300)

References:

1. APHA (1985). Compendium of Methods for the Microbiological Examination of Foods.
2. ISO 7899-2. Water quality—Detection and enumeration of intestinal enterococci.
3. Slanetz, L.W., and Bartley, C.H. (1957). J. Bacteriol. 74: 591-595.