Liofilchem® Chromatic™ E. coli O157

Liofilchem® Chromatic™ E. coli O157 is a selective chromogenic medium formulated for the isolation, differentiation, and presumptive identification of Escherichia coli O157, a pathogenic serotype associated with foodborne illness and hemorrhagic colitis.

This medium enables rapid detection of E. coli O157 colonies, which appear mauve to mauve-purple, distinguishing them from other non-O157 E. coli strains and Enterobacteriaceae.

It is designed for use in both clinical diagnostics and food safety testing, offering visual differentiation within 18–24 hours of aerobic incubation.

Key Features

• Chromogenic medium for selective isolation of E. coli O157.
• Distinct mauve-purple colony color for easy identification.
• Inhibits Gram-positive flora using sodium deoxycholate.
• Differentiates E. coli O157 from other E. coli and Enterobacteriaceae.
• Supports direct inoculation or use after enrichment.
• Rapid detection in 18–24 hours at 37°C.
• Suitable for clinical, food, and environmental microbiology laboratories.
• Compliant with international diagnostic and food safety testing standards.

Typical Formula (per litre)

Principle of the Method

• Peptones and extracts supply amino acids, nitrogen, and vitamins required for bacterial growth.
• Sodium chloride maintains osmotic equilibrium.
• Sodium deoxycholate selectively inhibits Gram-positive bacteria.
• Chromogenic mix provides enzyme-specific color reactions to distinguish E. coli O157 from other coliforms.
• Agar solidifies the medium for colony isolation and morphology evaluation.

Colonies of E. coli O157 appear mauve to mauve-purple, while non-O157 E. coli and Klebsiella form blue colonies.

Preparation

Dehydrated Medium

1. Suspend 49 g of powder in 1 L of distilled or deionized water.
2. Heat to boiling while stirring until completely dissolved.
3. Do not autoclave.
4. Cool to 45–50°C and pour into Petri dishes aseptically.

Medium in Bottles

1. Loosen the cap and melt in a water bath at 100°C until liquefied.
2. Tighten the cap, invert gently for uniformity, and cool to 45–50°C before pouring into Petri dishes.

Test Procedure

1. Inoculate by direct streaking or from pre-enriched samples.
2. Incubate aerobically at 37°C for 18–24 hours.
3. Examine colonies for characteristic mauve or mauve-purple coloration.

Interpretation of Results

Note: Some Salmonella spp. may produce false positives. Confirm suspected colonies using immunoserological or molecular methods (e.g., latex agglutination or PCR).

Quality Control

Incubation: 35 ± 2°C for 18–24 h (aerobic).

Appearance (Dehydrated): beige to faint pink, free-flowing powder.

Appearance (Prepared): slightly opalescent, light beige.

Storage and Stability

• Store dehydrated medium at 10–30°C in a dry, sealed container.
• Store plates and bottles at 2–8°C, protected from light.
• Shelf life:
  • Dehydrated medium – 2 years
  • Bottled medium – 1 year
  • Ready-to-use plates – 4 months

Safety and Handling

• For in vitro diagnostic use only.
• Use by qualified laboratory professionals under aseptic conditions.
• Handle biological materials per biosafety level 2 (BSL-2) practices.
• Consult the Safety Data Sheet (SDS) for safe handling instructions.
• Dispose of media and cultures following local and institutional biosafety regulations.

Ordering Information

Liofilchem® Chromatic™ E. coli O157 provides a rapid, reliable, and visually distinctive medium for isolating Escherichia coli O157 from clinical, food, and environmental samples. Its selective chromogenic formulation simplifies pathogen identification, ensuring consistent results for diagnostic laboratories, food safety agencies, and quality control testing following global public health standards.