Selection of bacterial strains in a testing microbiology laboratory for quality assurance purposes: ISO/IEC 17025:2017 standard point of view

Abstract

Clause 6.5 of the ISO/IEC 17025:2017 standard describes the requirements for the metrological traceability of measurement results of a testing or calibration laboratory. Subclause 6.5.2 describes three ways to establish traceability to the International System of Units (SI). However, it is not technically possible to trace the bacterial strains used in a microbiology laboratory to the SI unit. So, when selecting a bacterial strain in a microbiology laboratory for quality assurance purposes, the laboratory needs to fulfill the subclause 6.5.3 (a) of the ISO/IEC 17025:2017 standard i.e., the laboratory needs to utilize a certified bacterial strain provided by a competent producer. So, when procuring a bacterial strain to fulfill this subclause, we need to ensure two points; (a) the bacterial strain is certified and (b) the producer is competent. A certified bacterial strain produces well-defined biochemical reactions and possesses a defined genomic sequence. There are various well-known certified bacterial strains, such as American Type Culture Collection (ATCC) strains, National Collection of Type Cultures (NCTC) strains etc. The laboratory also needs to make sure that the producer of these certified bacterial strains is competent, i.e. ISO 17034 accredited. Only when these two conditions are met, a microbiology laboratory can safely assume that it meets the requirements of subclause 6.5.3 (a) of the ISO/IEC 17025:2017 standard. For a particular bacterial species, from the vast number of strains available, the laboratory also needs to consider which specific strain to procure. The purpose of this article is to discuss why a testing microbiology laboratory needs bacterial reference materials and how it should select a bacterial reference material for quality assurance purposes from the ISO/IEC 17025:2017 standard point of view.