Intrinsically resistant to Ampicillin.

Usually susceptible to: cephalosporins including first generation, Aminoglycosides, TMP-SMX, fluoroquinolones, and Pip-Tazo.

Almost always susceptible: Carbapenems, Aztreonam, Tigecycline, Colistin.

Resistant strains may be R to third generation cephalosporins (ESBLs), and rarely to carbapenems (i.e. carbapenemase enzymes).

Nitrofurantoin for UTI only, when confirmed susceptible