Liofilchem® Bromocresol Purple Azide Broth, 500g

Liofilchem® Bromocresol Purple Azide Broth is a selective confirmation medium used in the bacteriological analysis of water for the detection and confirmation of enterococci following a preliminary test with Azide Dextrose Broth (ref. 610003).

This medium is designed in accordance with Hajna’s buffered azide glucose-glycerol formulation (1951) and provides a reliable means of confirming the presence of fecal streptococci (enterococci) through selective inhibition and distinct color change due to glucose fermentation.

Key Features

• Selective and confirmatory medium for enterococci in water and wastewater testing.
• Buffered system maintains optimal pH for enterococcal growth.
• Bromocresol purple indicator provides a clear visual endpoint — color change from purple to yellow indicates positive glucose fermentation.
• Sodium azide selectively inhibits Gram-negative bacteria and non-enterococcal flora.
• Compliant with international water microbiology methods (APHA, Hajna & Perry).
• Long shelf life (4 years) and consistent quality for routine laboratory use.

Principle of the Method

• Tryptone and yeast extract supply nitrogen, amino acids, vitamins, and minerals for bacterial growth.
• Glucose serves as a fermentable carbohydrate; acid production from fermentation causes the color shift.
• Sodium chloride maintains osmotic equilibrium.
• Potassium phosphate salts act as buffers to stabilize pH.
• Sodium azide inhibits Gram-negative and many non-enterococcal Gram-positive organisms.
• Bromocresol purple, a pH indicator, shifts from purple (neutral) to yellow (acidic) in the presence of active fermentation.
• The addition of glycerol (5 mL/L) enhances glucose fermentation by enterococci.

Typical Formula (per litre)

Preparation

1. Suspend 36 g of powder in 1 L of distilled or deionized water.
2. Add 5 mL of glycerol, mix carefully, and distribute into tubes or bottles.
3. Sterilize at 115°C for 15 minutes.
4. Cool to room temperature before inoculation.

Test Procedure

1. Transfer three loops from each positive Azide Dextrose Broth tube into Bromocresol Purple Azide Broth tubes.
2. Incubate at 36 ± 1°C for up to 48 hours.
3. Examine for turbidity and color change.

Interpretation of Results

Quality Control

Dehydrated medium: homogeneous beige powder

Prepared medium: clear, light purple

Storage and Stability

• Store dehydrated powder at 10–30°C, protected from humidity and light.
• Shelf Life: 4 years.
• Do not use if product shows contamination, discoloration, or clumping.

Safety and Handling

• Contains sodium azide, classified as harmful.
• For professional use only by trained laboratory personnel.
• Handle under standard microbiological safety conditions.
• Dispose of waste according to local regulations.

Ordering Information

Liofilchem® Bromocresol Purple Azide Broth is a reliable confirmatory medium for verifying the presence of enterococci in water samples after enrichment in Azide Dextrose Broth. Its selective formulation, coupled with a distinct colorimetric pH response, allows clear and accurate confirmation of fecal streptococci. This medium is widely used in environmental and water microbiology laboratories for quality control and public health testing in compliance with international standards.