🦠 Determination and microbial characterization of the population of viable microorganisms (bioburden) on or in a health care product, component, raw material or package — representative selection of products and portions (SIP), neutralization or removal of inhibitory substances, removal of microorganisms (with assessment of its efficiency), culture under conditions chosen for the expected microorganisms and enumeration, applying a bioburden correction factor; excluding viruses, prions and protozoa and monitoring of the manufacturing environment, PN-EN ISO 11737-1

Microbiology PN-EN ISO 11737-1

Overview

WHAT THE STANDARD COVERS. We read the text of the standard in two iTeh samples: SIST EN ISO 11737-1:2018 (English text) — title page and European foreword of EN ISO 11737-1:2018 and the beginning of the ISO text — and ISO 11737-1:2018 (French version) — from the title page through the contents, foreword, introduction and Clauses 1–5 to 6.1.4 (culturing of microorganisms) on page 7 inclusive. Outside the samples remain enumeration of microorganisms (6.1.5), microbial characterization (6.2), validation of the method (7: correction factor, method suitability), routine determination and data interpretation (8), maintenance of the method (9) and the annexes (including A — guidance, B — assessment of release of microbicidal substances, D — division of responsibilities between manufacturer and laboratory). We did not read amendment A1 (ISO 11737-1:2018/Amd 1:2021).

ACCORDING TO THE TEXT OF ISO 11737-1:2018 AND THE FOREWORD OF EN ISO 11737-1:2018. The standard was prepared by ISO/TC 198 “Sterilization of health care products” in collaboration with CEN/TC 204 “Sterilization of medical devices” (secretariat BSI), under a mandate from the European Commission and EFTA; EN ISO 11737-1:2018 superseded EN ISO 11737-1:2006 and adopts ISO without modification. The third edition replaces the second (ISO 11737-1:2006) as a technical revision and incorporates the technical corrigendum ISO 11737-1:2006/Cor.1:2007; main changes: the term bioburden spikes was introduced as a normal part of bioburden with example data; it was clarified that packaging is generally not tested unless it is an integral part of the product; more information on the most probable number (MPN) technique; clarification of ways to improve the limit of detection and correct use of data; the part on statistical methods was removed; a table of criteria for selecting methods to determine recovery efficiency was added, the use of the correction factor explained and the recovery efficiency value < 50 % mentioned for technical changes removed; more information on the method suitability test; rules for direct plate counting, estimated counts and counts outside the ideal range were added; a table clarifying typical responsibilities of manufacturer and laboratory was added; more emphasis on a risk-based approach, including the intended use of bioburden data. Introduction: a product is sterile when free of viable microorganisms; standards for validation and control of sterilization require adventitious microbial contamination of a product before sterilization to be minimized; inactivation of microorganisms is often described by an exponential relationship, so there is always a finite probability that a microorganism survives, and the sterility of a product population is defined as the probability of a viable microorganism being present; the efficacy of sterilization cannot be fully verified by product testing, so processes are validated (ISO 14937, ISO 11135, ISO 11137, ISO 17665, ISO 14160), and validation and control require knowledge of the microbiological challenge — the number, characteristics and properties of microorganisms; bioburden — the population of viable microorganisms on or in a product and/or sterile barrier system — is used in validation and revalidation of sterilization processes, routine monitoring of manufacturing processes, monitoring of raw materials, components and packaging, assessing the efficiency of cleaning processes and in the environmental monitoring programme; it is the sum of contributions from raw materials, component manufacture, assembly, the manufacturing environment, utilities (e.g. compressed air, water, lubricants), cleaning processes and packaging; bioburden cannot be counted exactly — it is estimated by a defined method, and because of the diversity of products no single method or single removal technique can be defined for all situations; the document gives requirements and, in annexes, guidance — other methods may be used if they are effective in achieving compliance. Scope (1): requirements and guidance for the enumeration and microbial characterization of the population of viable microorganisms on or in a health care product, component, raw material or package; according to the note the nature and extent of characterization depend on the intended use of the data; the document does not apply to the enumeration or identification of viruses, prions or protozoa (including agents of spongiform encephalopathies) or to microbiological monitoring of the manufacturing environment. References (2): ISO 10012, ISO 13485, ISO 15189, ISO/IEC 17025. Terms (3) include: bioburden; bioburden correction factor — a numerical value applied to a viable count to compensate for incomplete removal and/or failure to culture microorganisms; bioburden estimate — established by applying that factor; method suitability — evaluation of the test method to demonstrate its ability to allow microbial growth; bioburden spike — a value significantly higher than others in a data set; culture conditions — combination of growth medium and incubation (temperature, time); recovery efficiency — the ability of a technique to remove, collect and/or culture microorganisms from a product; SIP (sample item portion) — a defined portion of a health care product tested; sterile barrier system; health care products — medical devices (including in vitro diagnostics) and medicinal products (including biopharmaceuticals). General requirements (4): bioburden procedures shall be specified; documents and records are reviewed and approved by designated personnel and controlled according to ISO 13485, ISO 15189 or ISO/IEC 17025; records of all original observations, calculations and reports are kept with the identity of the personnel who sampled, prepared and tested; calculations and data transfers are subject to checks; responsibility and authority shall be specified and, with several organizations with separate management systems, divided (Annex D); calibration of equipment according to ISO 13485, ISO 15189, ISO/IEC 17025 or ISO 10012; methods for preparing and sterilizing test materials with quality testing; measurement uncertainty, precision and bias generally do not apply to bioburden methods, and such analysis may not be needed except in assessing overall laboratory competence; procedures for investigating out-of-specification results and for correction, corrective and preventive action. Selection of products (5): the product shall be representative of routine production, including materials and packaging; grouping products into families requires a documented rationale; the time between manufacture and determination shall be considered, as bioburden can change over time; the whole product (SIP = 1,0) or a portion (SIP < 1,0) may be used, which shall adequately represent the bioburden of the whole — with uniform distribution any portion, with non-uniform distribution portions proportionally representing each material or the portion presenting the greatest challenge to sterilization, and with unknown distribution portions proportionally representing the materials; SIP may be chosen by length, mass, volume or surface area. Methods (6.1): the method shall suit the intended use of the data and include neutralization of inhibitory substances (if necessary), removal of microorganisms (if appropriate), culture and enumeration; if the product may release substances adversely affecting detection, a system to neutralize or remove (or minimize) their effect is used and its effectiveness established (Annex B); with removal, its efficiency is assessed and recorded, considering at least the ability of the technique to remove microorganisms, possible types and locations of microorganisms, the effect of the technique on their viability and the physical and chemical nature of the product; with direct culture of the product, the efficiency of enumeration is assessed; culture conditions are chosen after considering the expected microorganisms and the nature of the product, and the rationale is documented.

STATUS (as of 03.10.2026). The PKN search (term “PN-EN ISO 11737-1”, 03.10.2026) shows PN-EN ISO 11737-1:2018-03 in the Polish and English versions (“Introduces: EN ISO 11737-1:2018 [IDT], ISO 11737-1:2018 [IDT]”) and the amendment PN-EN ISO 11737-1:2018-03/A1:2021-11 in the Polish and English versions (“Introduces: EN ISO 11737-1:2018/A1:2021 [IDT], ISO 11737-1:2018/Amd 1:2021 [IDT]”), without a withdrawal note, and the withdrawn PN-EN ISO 11737-1:2007 (Polish version) and PN-EN ISO 11737-1:2006 (English version). In the iTeh catalogue (read on 03.10.2026) ISO 11737-1:2018 has the status “Published”, stage 90.92 (standard to be revised) since 02.01.2024, amended by ISO 11737-1:2018/Amd 1:2021.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database, load up to 17.09.2026, read on 03.10.2026). The number 11737-1 appears in 5 records at 5 laboratories: AB 774, AB 1531, AB 1575, AB 1629, AB 1763. In the current PCA documents (read on 03.10.2026, issues from 05.08.2025 to 31.08.2026) the number appears in 5 items — one at each laboratory; the PDF scope file of AB 1629 (issue No. 11) contains the five-page scope twice (10 pages, each marker from 1/5 to 5/5 twice), so this item is counted once; in the other four documents the number of page markers equals the number of PDF pages, without repetitions; a search of all 1291 PCA documents downloaded from BIP on 03.10.2026 found no laboratories outside the database copy (17 laboratories on the list have no link to a scope document on BIP). Forms: “PN-EN ISO 11737-1:2018-03” (AB 1629), “PN-EN ISO 11737-1:2018-03+A1:2021-11” (AB 1531), “PN-EN ISO 11737 -1:2018-03” with a space and a separate line for the amendment “/A1:2021-11” (AB 1763), “PN-EN ISO 11737-1 :2018” (AB 774) and “PN-EN ISO 11737-1” without year next to Ph. Eur. 2.6.12 (AB 1575). None of these items is suspended. The “Laboratories” tab (term “PN-EN ISO 11737-1”) shows 4 laboratories: AB 774, AB 1531, AB 1575 and AB 1629; AB 1763 is under “PN-EN ISO 11737 -1” (with a space before “-1”) — checked with tab queries on the production server labcoda.pl on 03.10.2026.

WHAT THE LABORATORIES TEST (items in PCA). Object: medical devices (AB 1531, AB 1763; at AB 1575 in the flexible scope of accreditation), medical devices — implants and instruments (AB 1629), other products: medicinal products, medical devices, biocidal products (AB 774). Characteristic: population of microorganisms (AB 774), determination of the population (number) of microorganisms on products (AB 1531), number of microorganisms (AB 1575), number of microorganisms, aerobic bacteria and fungi — yeasts and moulds (AB 1629), number of aerobic microorganisms (bacteria) on products (AB 1763). Technique: membrane filtration (AB 774, AB 1531, AB 1629, AB 1763), at AB 1575 also the plate method (pour plate).

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. With sample selection: a product not representative of routine production or without packaging when it is part of the product (5.1.1); undocumented product families (5.1.2). With time: bioburden changes between manufacture and testing (5.1.3). With SIP: a portion not representing the materials or omission of the portion with the greatest challenge (5.2). With inhibitory substances: substances released from the product can adversely affect detection of bioburden — a neutralizing system of established effectiveness is needed (6.1.2). With removal: incomplete recovery is compensated by the correction factor — the viable count is not yet the bioburden estimate (3.3, 3.4, 6.1.3). With culture: conditions are chosen after considering the expected types of microorganisms and the nature of the product, and the rationale is documented (6.1.4). With interpretation: bioburden spikes are a normal part of the data (foreword, 3.6).

WHAT WE DO NOT GIVE. We did not read the counting rules, microbial characterization, method validation (determination of the correction factor, method suitability), routine determination, data interpretation or maintenance of the method (6.1.5–9, annexes), nor amendment A1:2021. We do not give bioburden limits for devices.

Method principle

Microorganisms are removed from representative products (whole or as sample item portions, SIP) — after neutralizing growth-inhibiting substances — or the product is cultured directly; the microorganisms are cultured under conditions chosen for the expected types and counted (e.g. after membrane filtration). The viable count is converted with a correction factor, compensating for incomplete removal and culture, into the bioburden estimate of the product.

Applications

• Health care products, components, raw materials and packaging before sterilization (1)
• Validation and revalidation of sterilization processes, routine production control, assessment of cleaning efficacy (introduction)
• Medical devices, implants and instruments, medicinal and biocidal products — items in the accreditation scopes of 5 laboratories in PCA

Key parameters

Standard

Standard number

PN-EN ISO 11737-1:2018-03 (+A1:2021-11)

Title (PL)

Sterylizacja produktów medycznych — Metody mikrobiologiczne — Część 1: Oznaczanie populacji drobnoustrojów na produktach

Title (EN)

Sterilization of health care products — Microbiological methods — Part 1: Determination of a population of microorganisms on products

Step-by-step procedure

1. Selection of products

   Representative of routine production, with packaging if integral; product families justified; time since manufacture considered (5.1). PN-EN ISO 11737-1:2018-03 and A1:2021-11 without a withdrawal note (03.10.2026).

2. SIP

   Whole product or portion according to bioburden distribution (5.2).

3. Neutralization and removal

   Neutralization of inhibitory substances; removal with efficiency assessment or direct culture (6.1.2, 6.1.3).

4. Culture and enumeration

   Culture conditions chosen and justified (6.1.4); counting rules according to 6.1.5 (not read).

5. Result

   Bioburden estimate after applying the correction factor; validation and interpretation according to Clauses 7–8 (not read).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Work with microbial cultures — biosafety rules, aseptic technique
• Medical devices may be contaminated — gloves, decontamination of waste after culture

Frequently asked questions