The PCR assay (protocol 2) was tested on a selection of 20 strains (Table 1) by 7 different laboratories. Different PCR platforms were used; ABI7500 (Life Technologies), RotorgeneQ (Qiagen), Biorad CFX96 (Bio-Rad), and Lightcycler 480 (Roche). Also different DNA polymerases were used; PCR ReadyMix (Sigma), Platinum® Multiplex PCR Master Mix (Life Technologies), Fast start master (Roche), and Master Mix for PCR (Bio-Rad). All laboratories correctly detected the targeted carbapenemase genes, and no false positive results were found. With exception of CTX-M, which was not tested, or partially tested as is shown in Table 1, results of the multi-centre comparison were all concordant and again, the results were 100% concordant with listed strain characteristics.