Table 1.

Studies of I-R Susceptibilities of Select Gram-Negative Bacteria. MIC₅₀ and MIC₉₀ are the Minimum Inhibitory Concentrations for 50% and 90% of Isolates, Respectively. Imipenem Susceptibility is Based on FDA-Approved MIC Breakpoints as Follows: Enterobacterales, Susceptible (S) ≤1 µg/mL, Intermediate (I) 2 µg/mL, Resistant (R) ≥4 µg/mL; P. aeruginosa, S ≤2 µg/mL, I 4 µg/mL, R ≥8 µg/mL; A. baumannii, S <2 µg/mL, I 4 µg/mL, R >8 µg/mL; Anaerobic Bacteria, S ≤4 µg/mL, I 8 µg/mL, R ≥16 µg/mL

Organism	Number of Isolates	I-R MIC (μg/mL)		Percent Susceptible
		MIC50	MIC90
Enterobacterales
Non-proteeae Enterobacterales6	3143	0.12	0.5	99.1
CRE6	130	0.5	2	78.5
CRE29	62	NR	NR	71
CRE26	96	0.5	1	100
CRE27	200	≤0.25	0.5	NR
OXA-48-like CRE30	20	4	≥32	15
KPC Enterobacterales23	110	0.25	1	90.9
Colistin-resistant Enterobacterales27	97	≤0.25	≤0.25	NR
NDM Enterobacterales23	31	32	NR	0
Escherichia coli
E. coli17	10,866	NR	NR	99.9
E. coli21	2778	0.25	0.25	100
MDR E. coli17	2020	NR	NR	99.2
Klebsiella pneumoniae
K. pneumoniae17	3519	NR	NR	94.4
K. pneumoniae21	891	0.25	0.25	99.3
K. pneumoniae7	1591	0.12	1	94.8
KPC K. pneumoniae17	133	NR	NR	99.2
KPC K. pneumoniae21	111	0.25	1	97
KPC K. pneumoniae30	92	≤0.25	0.5	100
KPC K. pneumoniae31	295	0.25	1	98
CR K. pneumoniae7	179	2	>32	54.2
Enterobacter spp.
Enterobacter spp.21	211	0.25	0.5	99
Enterobacter spp.19	96	0.25	1	92
Enterobacter spp.7	772	0.12	0.5	96.8
E. cloacae17	944	NR	NR	95.8
CR E. cloacae17	49a	NR	NR	18.4
CR E. cloacae7	34	4	8	26.5
Serratia marcescens
Serratia marcescens23	9	1	8	67
Citrobacter spp.
Citrobacter spp.19	4	0.25	2	75
P. aeruginosa
P. aeruginosa21	490	0.5	2	98
P. aeruginosa8	845	0.5	2	94.2
P. aeruginosa17	1959	NR	2	93.9
P. aeruginosa7	1705	0.25	2	94.7
P. aeruginosa32	42	NR	1–64	64
P. aeruginosa35	538	0.25	2	91.5
P. aeruginosa36	1445	0.5	1	97.3
CR P. aeruginosa21	144	1	2	92
CR P. aeruginosa8	251	2	4	80.5
CR P. aeruginosa7	477	2	32	81.1
CR P. aeruginosa6	227	2	8	78
A. baumannii
A. baumannii21	158	2	>16	51
A. baumannii8	72	4	>32	45.8
A. baumannii7	486	32	>32	10.3
Anaerobic bacteria
B. fragilis39	38	0.125	2	NR
B. fragilis38	220	0.25	0.5	99.1
Bacteroides non-fragilis spp.38	231	0.25	1	99.6
B. cacae38	10	0.25	0.25	100
B. vulgatus38	22	0.5	1	100
B. uniformis38	22	0.25	0.5	100
B. ovatus38	43	0.25	0.5	100
B. thetaiotaomicron38	103	0.25	0.5	99
Parabacteroides distasonis38	24	0.5	1	100

Note: ^a81.6% (40/49) of isolates carried MBL and/or OXA-48-like carbapenemases.

Abbreviations: CR, carbapenem-resistant; CRE, carbapenem-resistant Enterobacterales; NDM, New Delhi metallo-beta-lactamase; NR, not reported.