Broad-spectrum (antipseudomonal) penicillin Piperacillin and piperacillin / tazobactam have activity against Bacteria susceptible to ampicillin Some strains of Enterobacter and Serratia species Many strains of P aeruginosa The addition of a beta-lactamase inhibitor enhances activity against beta-lactamase-producing methicillin-sensitive S aureus, E coli, K pneumoniae, H influenzae, and gram-negative anaerobic bacilli but not against gram-negative bacilli that produce AmpC beta-lactamase or KPC and may only partially inhibit ESBL produced by some K pneumoniae, E coli, and other Enterobacterales.