Almost always susceptible to:
Aminoglycosides
TMP-SMX
Fluoroquinolones
Carbapenems
Aztreonam
Tigecycline
Colistin
Fosfomycin and Nitrofurantoin for UTI (cystitis) only, when confirmed susceptible
Intrinsically resistant to Ampicillin
Resistant strains may be resistant to third generation cephalosporins (ESBLs), and rarely to carbapenems (i.e. carbapenemase enzymes)
