EN ISO 16649-3:2015 PDF

Overview

EN ISO 16649-3:2015 (Corrected version 2016-12-15) is a horizontal ISO/CEN standard for the microbiology of the food chain that specifies a liquid-medium detection and Most Probable Number (MPN) enumeration technique for β‑glucuronidase‑positive Escherichia coli using the chromogenic substrate 5‑bromo‑4‑chloro‑3‑indolyl‑β‑D‑glucuronide. The method includes incubation at (37 ± 1) °C followed by (44 ± 1) °C, and is intended for food, animal feed and environmental samples collected in food production and handling areas.

Key topics and technical requirements

• Scope: Applies to products intended for human consumption and animal feed, plus environmental sampling in food operations.
• Detection and enumeration: Uses a liquid enrichment technique with subculturing and MPN calculation to estimate cell numbers.
• Selective media and chromogenic detection: Relies on 5‑bromo‑4‑chloro‑3‑indolyl‑β‑D‑glucuronide for identifying β‑glucuronidase activity.
• Incubation regime: Sequential incubation at 37 ± 1 °C and then 44 ± 1 °C as part of detection/enumeration.
• Procedure format: Typical MPN approach involves inoculating multiple tubes (e.g., three or five tube series of double‑strength medium) and calculating MPN per test portion.
• Performance considerations: Method reports include precision information and guidance for interpreting results (see Clause 11).
• Limitations:
  • Susceptible to variability-results must be interpreted in context.
  • Not fully validated for all matrices (e.g., some milk and milk products). For milk, ISO 7251 is recommended.
  • Some pathogenic E. coli (e.g., β‑glucuronidase‑negative strains such as E. coli O157 and strains that do not grow at 44 °C) will not be detected by this method.

Applications and users

• Food microbiology and quality control laboratories performing E. coli enumeration for regulatory compliance, HACCP verification, shelf‑life studies, and product release testing.
• Environmental monitoring teams in food production, processing and handling facilities for hygiene verification.
• Feed producers and testing labs assessing contamination in animal feed.
• Contract testing laboratories and public health agencies that require a standardized MPN detection method for β‑glucuronidase‑positive E. coli.

Related standards

• ISO 16649-1 - Colony‑count technique at 44 °C using membranes and the same chromogenic substrate.
• ISO 16649-2 - Colony‑count technique at 44 °C using the chromogenic substrate.
• ISO 7251 - Recommended method for E. coli in milk and milk products (useful when ISO 16649-3 is not validated for a matrix).

Keywords: EN ISO 16649-3:2015, E. coli enumeration, beta‑glucuronidase, MPN technique, 5‑bromo‑4‑chloro‑3‑indolyl‑β‑D‑glucuronide, food microbiology, horizontal method, ISO 16649.