TABLE 1.

MIC₅₀s, MIC₉₀s, and percent antimicrobial susceptibilities of 97 samples of P. aeruginosa^a

Antimicrobial agent	Breakpointsb (μg/ml)			Mucoid strains (n = 40)			Nonmucoid strains (n = 57)			P (Fisher exact test)
	S	I	R	MIC50 (μg/ml)	MIC90 (μg/ml)	% Susceptibility	MIC50 (μg/ml)	MIC90 (μg/ml)	% Susceptibility
Ceftizoximec	≤8	16–32	≥64	>32	>32	7.5	32	>32	5.3	0.65
Ceftazidime	≤8	16	≥32	4	>32	70.0	2	16	89.5	0.096
Cefotaximec	≤8	16–32	≥64	32	>64	25.0	32	>64	14.0	0.173
Ceftriaxonec	≤8	16–32	≥64	32	>64	27.5	64	>64	21.0	0.464
Cefoperazon	≤16	32	≥64	16	>32	57.5	3	>32	79.0	0.00086d
Cefepime	≤8	16	≥32	16	>16	42.5	4	16	83.0	0.000047d
Imipenem	≤4	8	≥16	1	4	90.0	1	2	96.5	0.19
Ampicillin-sulbactamc	≤8–4	16–8	≥32–16	>32–16	>32–16	5.0	>32–16	>32–16	1.7	0.365
Ciprofloxacin	≤1	2	≥4	1	>4	50.0	≤0.25	2	86.0	0.00012d
Aztreonam	≤8	16	≥32	8	>32	50.0	4	32	84.0	0.00031d
Amoxicillin-clavulanatec	≤8–4	16–8	≥32–16	>32–16	>32–16	2.5	>32–16	>32–16	1.7	0.800
Ticarcillin-clavulanate	≤64–2		≥128–2	≤16	128	87.5	≤16	128	80.7	0.376
Mezlocillin	≤64		≥128	64	>128	52.5	32	>128	70.2	0.077
Sparfloxacin	≤1	2	≥4	2	>2	30.0	1	>2	68.4	0.00020d
Piperacillin-tazobactam	≤64–4		≥128–4	≤8	>64	80.0	≤8	64	89.5	0.19
Netilmicin	≤8	16	≥32	8	>16	50.0	8	>16	56.0	0.55
Meropenem	≤4	8	≥16	≤1	2	95.0	≤1	2	98.0	0.365
Azlocillin	≤64		≥128	≤64	>65	62.5	≤64	>64	84.2	0.015

^aAll samples were resistant to cefoxitin and cefpodoxime. 

^bBased on interpretive breakpoints as indicated in NCCLS document M100-S10 (M7) (20) S. susceptible; I, intermediate; R, resistant. 

^cDrug not indicated for treatment of P. aeruginosa infections, even with susceptibility (19). 

^dThe difference in the susceptibility rates between the mucoid and nonmucoid groups was considered statistically significant.