Comparison of disc diffusion, Etest and broth microdilution for testing susceptibility of carbapenem-resistant P. aeruginosa to polymyxins

Table 1 Activities of ten agents against 109 isolates of carbapenem-resistant P. aeruginosa isolates obtained from patients with BSI over a six-year period.

Agent	MIC₅₀ μg/mL	MIC₉₀ μg/mL	Range μg/mL	% Susceptibility
Aztreonam	64	128	1 – >128	7.4
Cefepime	32	128	<0.25 – >128	7.3
Ceftazidime	128	>128	<0.25 – >128	8.3
Ciprofloxacin	32	64	<0.25 – 64	6.4
Colistin	1	1	<0.25 – 2	100
Gentamicin	>128	>128	0.5 – >128	20.2
Imipenem	64	256	16 – 1,024	0
Meropenem	32	256	2 – 1,024	1.8
Piperacillin/Tazobactam	>128	>128	1 – >128	13.8
Polymyxin B	0.5	1	<0.25 – 8	99.1