ISO 11731-2017 PDF

Full title and description

St ISO 11731-2017 — Water quality — Enumeration of Legionella. This International Standard specifies culture-based methods for the isolation and enumeration of Legionella spp. from water and water-related matrices (potable, industrial, waste and natural waters, biofilms, sediments and similar matrices), providing procedures for sample concentration, selective and non-selective plating, and confirmation of presumptive colonies.

Abstract

ISO 11731:2017 defines reference culture methods to detect and estimate numbers of culturable Legionella in environmental and potable water samples. It describes concentration techniques (for example membrane filtration), treatment options (heat and acid), plating on selective (e.g., GVPC) and non‑selective (BCYE) media, incubation and confirmation procedures, and highlights limitations (not all Legionella are culturable so some species will not be recovered by these methods).

General information

• Status: Published (current edition confirmed).
• Publication date: May 2017.
• Publisher: International Organization for Standardization (ISO).
• ICS / categories: 07.100.20 (Water quality).
• Edition / version: Edition 2 (ISO 11731:2017).
• Number of pages: 38 pages.

Scope

The standard applies to culture-based isolation and enumeration of Legionella spp. in water and water-related matrices. It presents procedures for direct plating and for concentration (e.g., membrane filtration), optional pretreatments (heat, acid), selection of agar media (non‑selective BCYE and selective media such as GVPC), incubation times/temperatures and subsequent confirmation of presumptive colonies. The document notes that some Legionella species are non‑culturable with current methods and therefore will not be detected by these procedures.

Key topics and requirements

• Sample handling and concentration (membrane filtration and elution) to increase detection sensitivity.
• Treatment options to reduce background flora — heat treatment and acid treatment procedures.
• Use of non‑selective BCYE agar and selective media (for example GVPC) for isolation and enumeration.
• Colony incubation periods (extended incubation up to 7–10 days) and counting of presumptive colonies.
• Confirmation of presumptive Legionella colonies (subculture on BCYE with/without L‑cysteine, serological or molecular confirmation as supplementary methods). Note: confirmation practice and combined confirmation approaches have been discussed in the literature because subculture alone can produce false positives.
• Quality assurance, reporting in CFU per unit volume, and laboratory competence requirements (laboratories performing Legionella culture are commonly expected to hold ISO/IEC 17025 accreditation or equivalent).
• Limitations and interpretation: only culturable Legionella are detected; results can vary by method combination and sample matrix, and combining complementary methods increases detection likelihood.

Typical use and users

Environmental and public health laboratories, hospital and healthcare facility water-safety teams, water utilities, cooling‑tower and building‑services contractors, accredited testing laboratories, consultants performing routine monitoring or outbreak investigations, and researchers validating or comparing Legionella detection methods. The standard is used for regulatory compliance, routine surveillance and investigative testing.

Related standards

Previous withdrawn editions include ISO 11731:1998 and related documents (for example earlier part ISO 11731‑2:2004). ISO 11731:2017 was prepared by ISO/TC 147/SC 4 (water microbiology). Related normative references and laboratory competence standards frequently used alongside ISO 11731 include ISO/IEC 17025 (laboratory accreditation) and other national/adopted variants such as EN/PN‑EN adoptions of ISO 11731:2017. Discussions on confirmation and laboratory practice also reference ISO 13843 (method validation/performance).

Keywords

Legionella, Legionella pneumophila, water quality, enumeration, culture method, BCYE, GVPC, membrane filtration, concentration, heat treatment, acid treatment, environmental monitoring, Legionnaires' disease.

FAQ

Q: What is this standard?

A: ISO 11731:2017 is an international standard that specifies culture methods for the isolation and enumeration of Legionella species from water and related matrices.

Q: What does it cover?

A: It covers sample concentration (e.g., membrane filtration), optional pretreatments (heat/acid), plating on selective and non‑selective media (BCYE, GVPC), incubation, colony counting and recommended confirmation procedures; it also describes method limitations.

Q: Who typically uses it?

A: Accredited environmental and public health laboratories, hospital water-safety teams, water utilities, cooling-tower operators, consultants and researchers involved in Legionella surveillance, compliance testing and outbreak investigations.

Q: Is it current or superseded?

A: The 2017 edition (Edition 2) is the current published edition (ISO 11731:2017); earlier editions, including ISO 11731:1998, have been withdrawn. The standard is subject to periodic review by ISO.

Q: Is it part of a series?

A: ISO 11731 has earlier and related parts/versions historically (for example ISO 11731:1998 and ISO 11731‑2:2004 which were superseded or withdrawn). National and regional bodies may publish adopted versions (e.g., EN/PNE standards) and companion documents on validation and laboratory practice are commonly used alongside it.

Q: What are the key keywords?

A: Legionella, Legionella pneumophila, enumeration, culture, membrane filtration, BCYE, GVPC, water monitoring, environmental microbiology.