Overview
EN ISO 21528-2:2017 (ISO 21528-2:2017, corrected version 2018-06-01) is a horizontal standard for the microbiology of the food chain that specifies the colony-count technique for the detection and enumeration of Enterobacteriaceae. The method is intended for products intended for human consumption and animal feed, and for environmental samples from primary production, food production and food handling. Use this colony-count technique when expected counts are greater than 100 colony‑forming units (CFU) per gram or millilitre. For lower counts, the MPN technique in ISO 21528‑1 is generally recommended.
Key topics and technical requirements
- Scope and applicability: Foods, animal feeding stuffs and relevant environmental samples in the food chain.
- Principle: Prepare an initial suspension and decimal dilutions, plate appropriate dilutions, incubate, count colonies and perform confirmation tests on selected colonies.
- Sample preparation: Follows ISO 6887-series guidance for test portions, suspensions and dilutions.
- Culture media and reagents: Specified media/reagents are listed (see Annex A) and used for selective isolation and confirmation.
- Procedure steps:
- Preparation of initial suspension and decimal dilutions
- Inoculation and incubation of plates
- Colony counting and selection for confirmation
- Subculturing and biochemical confirmation (including oxidase reaction and fermentation tests)
- Calculation and expression of results
- Confirmation: The 2017 revision replaced glucose agar with glucose OF medium in the confirmation step.
- Performance characteristics: Method validation data, interlaboratory study results, repeatability and reproducibility limits are included (informative annex).
- Quality and safety: Laboratory competence, appropriate equipment and biosafety practices are required (tests must be done under skilled microbiologist supervision).
Applications and users
- Food and feed testing laboratories performing routine hygiene and quality control (QC).
- Regulatory agencies and inspection bodies verifying compliance with microbiological criteria.
- Primary producers and food manufacturers monitoring environmental contamination and product safety.
- Contract testing and third‑party labs offering Enterobacteriaceae enumeration services.
- Use cases: shelf‑life studies, process hygiene monitoring, environmental swabbing programs, raw material screening and product release testing.
Related standards
- ISO 21528‑1 - Most probable number (MPN) technique for Enterobacteriaceae (for counts
