Characterization of methicillin-resistant Staphylococcus aureus displaying increased MICs of ceftaroline.

Methods: During the 2008 Assessing Worldwide Antimicrobial Resistance Evaluation (‘AWARE’) surveillance programme, four S. aureus collected from separate patients in Athens, Greece, demonstrated ceftaroline MICs of 4 mg/L. These isolates were clonally related and one strain (13101) was selected for further characterization. Two strains (4981 and 4977) displaying ceftaroline MICs of 1 and 2 mg/L, respectively, were included for comparison. All strains originated from the same hospital. Penicillin-binding protein (PBP) affinities for ceftaroline and comparators were determined. Strains were typed by single-locus typing (i.e. spa typing), multilocus sequence typing (‘MLST’) and by multiple-locus variable-number tandem repeat fingerprinting (MLVF). The presence of Pantone–Valentine leucocidin and the staphylococcal cassette chromosome mec types was assessed. We also performed nucleotide sequencing of the mecA (encoding PBP2a) promoter and ribosomal binding site (rbs) regions and mecR1.