In this study, the VITEK system produced the highest number of linezolid test errors among automated systems. The categorical and essential agreements amounted to 85.9% in total. There were five very significant errors for S. aureus isolates, including strains 3213, 3487, 3036 and 5721, organisms for which there are problems on several systems (Table 2),2) and strain 8053. There were also three very significant errors with the E. faecium isolates (3419, 8766 and 0006). An S. aureus isolate (1458) was unable to grow twice in VITEK maps, although it grew in all other automated systems. Another sensitive S. aureus (1909) isolate was declared non-sensitive (MIC – 8 g/ml) in original and new tests. There were six minor errors with enterococci, most of which were not sensitive (i.e.

moderate or resistant) due to micro-dilution of broth and were declared vulnerable by VITEK. The VITEK system also had the highest number of significant compliance errors, particularly for staphylococci that were properly declared sensitive, but for which linezolid MICs were reported at 4 g/ml instead of ≤1 g/ml. As a general rule, the FDA recommends defining the performance characteristics of your AST device in accordance with the standard CLSI reference method for each antimicrobial and the organisms to be tested. Since deviations in test procedures can affect performance, we believe you should conduct agree studies on all procedural options contained in the instructions for the usage section of the package. These treatment methods include, for example, vaccine preparation methods and reading of results: due to differences in CLSI versions used in each AST system, all data from each hospital was imported into WHONET 5.6 software and interpreted by CLSI 2017 to ensure consistency.8 The BMD results were considered a baseline. The Core Agreement (EA) was defined as a percentage of MOC as part of a single doubling of the corresponding DMD results.