ISO 21528-2-2017 (2018) PDF

Full title and description

ISO 21528-2:2017 — Microbiology of the food chain — Horizontal method for the detection and enumeration of Enterobacteriaceae — Part 2: Colony‑count technique. This international standard specifies a colony‑count (plate) method for enumerating Enterobacteriaceae in food, animal feed and related environmental samples.

Abstract

Specifies a horizontal colony‑count technique to enumerate Enterobacteriaceae in products intended for human consumption and animal feed and in environmental samples from primary production, food production and food handling. The method is intended where the expected count is greater than about 100 colony‑forming units per gram or millilitre; for lower expected counts ISO 21528‑1 (MPN technique) is generally used. The published text was corrected in mid‑2018.

General information

• Status: Published (International Standard).
• Publication date: Edition 2 published June 2017; corrected version issued July 2018 (corrections to the published text).
• Publisher: International Organization for Standardization (ISO).
• ICS / categories: 07.100.30 — Food microbiology.
• Edition / version: Edition 2 (2017).
• Number of pages: 15 pages (official ISO publication).

Scope

Defines a colony‑count plating procedure (horizontal method) for the detection and enumeration of Enterobacteriaceae in food and feed products and in environmental samples related to food production and handling. The technique is intended for samples where counts are expected to exceed approximately 100 cfu per g or mL; for lower counts the MPN procedure in ISO 21528‑1 is recommended.

Key topics and requirements

• Scope and intended use: enumeration of Enterobacteriaceae in foods, feeds and environmental samples when higher counts are expected.
• Colony‑count (plate) technique: preparation of test portions, serial dilution, inoculation onto appropriate selective/differential agar, incubation and colony counting.
• Decision criteria: guidance on count ranges for reliable enumeration (plate count ranges and when to use MPN instead).
• Quality and procedural controls: requirements for laboratory practice to ensure reliable results (sample handling, dilution accuracy, incubation conditions and result expression).
• Relationship to ISO 21528‑1: complementary method for low counts (MPN).

Typical use and users

Used by food and feed microbiology laboratories, quality assurance/control teams in food production, regulatory and inspection laboratories, and public‑health testing facilities for routine enumeration of Enterobacteriaceae in product and environmental monitoring programs. The standard provides a harmonized method for comparability of results between laboratories.

Related standards

Closely related to ISO 21528‑1 (Microbiology of the food chain — Horizontal method — Part 1: MPN technique for low counts). ISO 21528‑2 (2017) replaces ISO 21528‑2:2004; national and regional adoptions exist (for example EN ISO 21528‑2:2017 / adoptions in various member bodies).

Keywords

Enterobacteriaceae, colony count, plate count, enumeration, food microbiology, horizontal method, CFU, ISO 21528, MPN (ISO 21528‑1), food safety.

FAQ

Q: What is this standard?

A: An ISO international standard specifying a colony‑count method for the detection and enumeration of Enterobacteriaceae in food, feed and related environmental samples (ISO 21528‑2:2017, Edition 2).

Q: What does it cover?

A: The standard covers sample preparation, serial dilution, plating on suitable media, incubation and counting procedures for reliable enumeration where higher counts are expected (generally >100 cfu/g or mL). It clarifies when the MPN method (ISO 21528‑1) should be used instead.

Q: Who typically uses it?

A: Food and feed testing laboratories, quality assurance teams in the food industry, regulators and public‑health laboratories involved in microbiological monitoring and compliance.

Q: Is it current or superseded?

A: ISO 21528‑2:2017 (Edition 2) is the current published version; a corrected text was issued in July 2018. The standard was reviewed and confirmed (status 90.93) in 2025, so the 2017 edition remains the active ISO document as of its 2025 confirmation. (Check your national standards body for local adoption dates and any more recent amendments.)

Q: Is it part of a series?

A: Yes — it is Part 2 of ISO 21528 (series) dealing with Enterobacteriaceae; Part 1 (ISO 21528‑1) covers the MPN technique for lower counts. National/regional adoptions may be published as EN ISO or identical national publications.

Q: What are the key keywords?

A: Enterobacteriaceae; colony‑count; plate method; enumeration; food microbiology; CFU; ISO 21528; horizontal method; MPN (for related Part 1).