A β-lactamase inhibitor (IC50s = 8, 80, and 38 nM for TEM-1, P99, and KPC-2 β-lactamases, respectively); restores antimicrobial activity of ceftazidime, ceftriaxone, imipenem and piperacillin in vitro (MIC90 reduction 4-1024-fold across 190 E. coli and K. pneumoniae clinical isolates)