Intrinsically resistant to Ampicillin.

Generally susceptible: amoxicillin-clavulanate, cefixime, ceftriaxone, piperacillin-tazobactam, carbapenems, ciprofloxacin, TMP-SMX, aminoglycosides.

May be resistant to third generation cephalosporins (ESBL), and rarely to carbapenems (CRE including KPC).

Variable susceptibility: cefazolin, nitrofurantoin (cystitis only)