Abstract Purpose Nocardiosis is a rare but serious infection occurring predominantly in immunocompromised patients. The CLSI microdilution antimicrobial susceptibility testing is recommended for all nocardioses. Ready-to-use plates are available (Sensititre™ RAPMYCOI), but antimicrobials of interest (e.g. tedizolid, meropenem) are lacking. At the request of the French nocardiosis reference medical biology laboratory, a plate including meropenem and tedizolid was produced (Sensititre™ FRNOCAR1). Methods FRNOCAR1 was compared to RAPMYCOI using 133 clinical Nocardia isolates containing predominantly N. farcinica (23.3%), N. cyriacigeorgica (24.8%), and N. nova complex (21.1%). Acceptability was assessed using the FDA criteria (essential/category agreement; major, and very major error VME rates). Results All criteria were respected for 6 antimicrobials; for 5, the upper limit of the VME rate exceeded the criteria, despite a point estimate of 0.0%, due to a lack of resistant strains in the collection. For linezolid, the VME rate could not be calculated due to the absence of linezolid-resistant strains. Tedizolid minimal inhibitory concentration (MIC)50/MIC90 were 2–3 dilutions lower than that of linezolid (0.5/0.5 µg/mL and 2/4 µg/mL, respectively). Imipenem was better than meropenem for N. farcinica ; meropenem MIC was at least 2-dilutions lower than that of imipenem for N. gamkensis (8/8), N. gipuzkoensis (2/4), and N. wallacei (4/6). Conclusion For the antimicrobials common to both plates, the FRNOCAR1 demonstrated good agreement compared with RAPMYCOI. FRNOCAR1 includes tedizolid and meropenem, for which MIC could be reported upon justified request, with a comment indicating that these results are pending further validation.
Dutarte et al. (2026) studied this question.