These bacteria have inducible, chromosomal beta-lactamase genes known as AmpC (also referred to as IBLs for Inducible Beta Lactamase). They can develop resistance to all penicillins including piperacillin-tazobactam and all cephalosporins including ceftriaxone. These agents must not be used for serious infections. The exception is ceftriaxone which may be carefully used for UTIs if reported as susceptible.
Carbapenems are the only reliably active agents and should be used for serious infections until susceptibilities are known. If susceptible to fluoroquinolones they are generally excellent therapeutic alternatives.