CHROMagar™ O157

For the Selective Isolation and Differentiation of Escherichia coli O157

CHROMagar™ O157 is a selective chromogenic culture medium designed for the isolation, detection, and differentiation of E. coli O157:H7 and O157:H- from food, clinical, and environmental samples. Colonies of E. coli O157 develop a distinctive mauve coloration, while non-O157 E. coli and other bacteria appear blue, colorless, or are inhibited, enabling rapid and accurate identification.

As a reliable alternative to Sorbitol MacConkey Agar (SMAC), CHROMagar™ O157 offers superior specificity and clarity, reducing false positives and simplifying colony interpretation in surveillance, food safety, and clinical microbiology applications.

🔹 Key Features & Benefits

• ✅ Rapid & Distinctive Color-Based Differentiation:

  Organism	Colony Appearance
  E. coli O157	Mauve
  Other bacteria	Blue, colorless, or inhibited

• ✅ Superior to SMAC:
  • Unlike Sorbitol MacConkey agar, which can give false positives (e.g., Proteus, E. hermannii), CHROMagar™ O157 allows clear, easy identification of E. coli O157.
  • Maintains stable colony color even with extended incubation.
• ✅ High Sensitivity:
  • E. coli O157 detection sensitivity: ~89%*
    (Bettelheim, 1998 – J. Appl. Microbiol. 85: 425–428)
• ✅ Flexible Format Options:
  • Available in powder for in-house preparation, allowing better cost control and adaptability in testing volume.

🔹 Intended Use

CHROMagar™ O157 is intended for:

• Selective isolation and presumptive identification of E. coli O157 from:
  • Food samples (e.g., ground beef, produce, dairy, fermented milk)
  • Animal feces and compost
  • Human stool samples
  • Environmental swabs and water
• Suitable for:
  • Food safety testing
  • Public health surveillance
  • Veterinary and agricultural microbiology
  • Environmental monitoring

⚠️ Not intended for clinical diagnosis or treatment guidance. Confirmatory testing (e.g., latex agglutination, PCR, MALDI-TOF) is recommended for suspect colonies.

🔹 Clinical & Food Safety Context

E. coli O157:H7 is the most well-known Shiga toxin-producing E. coli (STEC) serotype and can cause:

• Hemorrhagic colitis (bloody diarrhea)
• Hemolytic uremic syndrome (HUS)
• Severe foodborne illness outbreaks

The organism is zoonotic, often transmitted through:

• Undercooked meat, raw vegetables, unpasteurized milk
• Direct contact with animals or contaminated environments

📌 WHO estimates ~70,000 infections globally per year attributed to E. coli O157.

🔹 Test Procedure

1. Sample Preparation: As per ISO 16654 or validated lab protocol
2. Inoculation: Direct plating or after selective enrichment (e.g., mTSB)
3. Incubation:
   • Temperature: 35–37 °C
   • Time: 18–24 hours
   • Atmosphere: Aerobic
4. Interpretation:
   • Mauve colonies = Presumptive E. coli O157
   • Further confirmation required

🔹 Ordering Information

🔹 Storage & Shelf Life

• Storage: 2–8 °C, dry, protected from light
• Shelf Life: Up to 24 months from production
• Prepared Plates: Use within recommended timeframe (see IFU)

🔹 Scientific Publications

• USDA, 2016 – Enumeration of E. coli O157:H7 in compost and manure
• Parsons et al., 2016 – Characterization of Shiga toxin-producing E. coli
• Njage et al., 2012 – Detection of O157 and non-O157 STEC in camel milk
• Bettelheim, 1998 – Evaluation of CHROMagar™ O157 specificity and reliability

CHROMagar™ O157 provides a fast, specific, and user-friendly solution for the detection of E. coli O157:H7, a major foodborne pathogen. With clear visual differentiation, reduced false positives, and flexibility in preparation, this medium is an essential tool for food industry labs, public health institutions, and research settings focused on STEC surveillance and prevention.