A broad-spectrum β-lactam antibiotic; active against Gram-negative and Gram-positive bacteria, including Enterococcus species, E. coli, and P. mirabilis (MIC50s = 0.5-2 μg/ml) as well as gentamicin-susceptible and -resistant strains of P. aeruginosa (MIC50s = 8 and 125 μg/ml, respectively); active against P. aeruginosa 46220 when used alone or in combination with tazobactam (ED50s = 1.58 and 1.34 mg/animal, respectively) in a mouse model of systemic infection; less active against P. aeruginosa 46220 DR-2 when used alone than when used in combination with tazobactam (ED50s = >20 and 4.39 mg/animal, respectively) in a mouse model of systemic infection