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This study evaluated the affinity of ceftaroline and comparator β-lactams for penicillin-binding proteins (PBPs) of methicillin-susceptible Staphylococcus aureus (MSSA), methicillin-resistant S. aureus (MRSA) and Streptococcus pneumoniae with varying susceptibility to penicillin. Ceftaroline is currently in Phase 3 development for the treatment of complicated skin and skin structure infections and community-acquired pneumonia, including infections caused by MRSA and multidrug-resistant S. pneumoniae.Binding affinities (IC50s) of ceftaroline, ceftriaxone, oxacillin and penicillin G for PBPs were measured in a competition assay by adding various concentrations of the test drugs to membranes or whole cells. PBPs were labelled using the fluorescent reporter molecule Bocillin FL.Overall, ceftaroline exhibited greater binding affinity for the range of PBPs tested, as compared with comparator β-lactams. The high affinity of ceftaroline for PBPs 1–3 of MSSA and PBP2a of MRSA correlates well with its efficacy against these organisms, as determined by MIC. Similarly, efficient binding of ceftaroline to key S. pneumoniae PBPs, such as PBP2x/2a/2b, taken together, correlates well with its low MICs for penicillin-resistant isolates of S. pneumoniae.The high affinities of ceftaroline for MRSA PBP2a, MSSA PBPs 1–3 and S. pneumoniae PBP2x/2a/2b support the potential efficacy of ceftaroline in the treatment of infections caused by MRSA and S. pneumoniae.