Multi-center and multi-method evaluation of in vitro activities of ceftaroline against S. aureus

This five-site study was performed to assess the reproducibility of ceftaroline MIC and disk results for Staphylococcus aureus. Three commercial broth microdilution, three gradient diffusion and ceftaroline 5 μg disk diffusion methods were compared to a reference broth microdilution method against challenge isolates (n = 41) and isolates collected at four European sites (n = 30/site). For four MIC methods (Sensititre and three gradient diffusion methods), 99.0% of consolidated MIC results were within +/− 1 dilution of the reference MIC. Categorical agreement rates based on EUCAST breakpoints for the challenge isolates were 75.6-100% and for disk testing were 78.0-92.7%. There was no clear distinction between isolates with MIC results of 1 and 2 mg/L with regard to variation in MIC or molecular genotyping results. The addition of an intermediate category for isolates with MIC results of 2 mg/L would help to identify these isolates as borderline susceptible/non-susceptible isolates.