The 31st EURL-AR Proficiency Test: Antimicrobial susceptibility testing of Escherichia coli, Salmonella and Campylobacter 2023

As the EU Reference Laboratory for Antimicrobial Resistance (EURL-AR), the National Food Institute (DTU Food) conducted in Autumn 2023 the 31st Proficiency Test (PT) for the antimicrobial susceptibility testing (AST) of commensal and zoonotic bacteria. The EURL-AR is accredited by the Danish Accreditation Fund (DANAK) as provider of PTs for the identification, serotyping and AST of zoonotic pathogens and indicator organisms, with accreditation number 516.

The EURL-AR PT for AST has been carried out annually since 2006 and aims to: i) monitor the quality of AST results produced by the participating National Reference Laboratories (NRL-AR), ii) identify NRL-AR’s which may need assistance to improve their performance in AST and iii) determine possible topics for further research or collaboration. The overall aim of the EURL-AR PT for AST has been to evaluate and improve the comparability of the Antimicrobial Resistance (AMR) surveillance data reported to the European Food Safety Authority (EFSA) by the different NRL-ARs, as part of the official EU AMR monitoring [1].

In the 31st EURL-AR PT for AST, eight strains of each of the following three organisms were included: Escherichia coli, Salmonella, and Campylobacter. More specifically, the present PT includes the following four components:

1. AST by broth microdilution (BMD) of 8× E. coli, 8× Salmonella and 8× Campylobacter test strains, determination of the Minimum Inhibitory Concentration (MIC) value as well as phenotype interpretation for each strain as “Susceptible” (S) or “Resistant” (R) to a specific
panel of antimicrobials for each organism.

2. AST by BMD of specific reference bacterial strains for each organism and evaluation of the obtained MIC values based on the QC ranges published in the most updated guidelines from the Clinical and Laboratory Standards Institute (CLSI) [2, 3].

3. Identification of the β-lactam resistance mechanism phenotype of the relevant E. coli and Salmonella strains, as Extended-Spectrum-β-Lactamase-producing (ESBL), AmpC-β-lactamase-producing (AmpC) and Carbapenemase-producing phenotypes, based on BMD data.

4. Identification of the bacterial species of the Campylobacter strains as C. jejuni or C. coli.

The results of the 31st EURL-AR PT for AST are presented in this report, which is approved in its final version by a technical advisory group composed by representatives from all NRL-AR’s, who meet annually at the EURL-AR workshop. The present report, at its final version, is publicly available at the EURL-AR website (https://www.eurl-ar.eu/reports.aspx).