(b).

Gram negatives	Ampicillin-sulbactam	Piperacillin tazobactam	Cefazolin	Cefepime	Ceftazidime	Ceftriaxone	Ertapenem	Meropenem	Amikacin	Gentamicin	Tobramycin	Ciprofloxacin	Minocycline	Aztreonam	Colistin
E. coli	X	X	X	X	X	X	X	X	X	X	X	X		X	X
Klebsiella spp.		X	X	X	X	X	X	X	X	X	X	X		X	X
Enterobacter spp.		X		X	X	X	X	X	X	X	X	X		X	X
Proteus spp.		X		X	X	X	X	X	X	X	X	X		X
Citrobacter spp.		X		X	X	X	X	X	X	X	X	X		X	X
S. marcescens		X		X	X	X	X	X	X	X	X	X		X
A. baumannii	X	X		X				X	X			X	X		X
P. aeruginosa		X		X	X			X	X	X	X	X		X	X