Table 3.

Antimicrobial activity against the genetically screened isolates of meropenem-non-susceptible Enterobacteriaceae (N=1375) collected as part of the INFORM programme (2015–17)

Organism group and antimicrobial	MIC50 (mg/L)	MIC90 (mg/L)	MIC range (mg/L)	MIC interpretation
				S (%)	I (%)	R (%)
Carbapenemase positive (MBL negative)a (n=910)d
ceftazidime/avibactam	1	2	≤0.015–16	99.8	—	0.2
ceftazidime	128	≥256	0.25 to ≥256	2.1	2.5	95.4
cefepime	≥32	≥32	0.12 to ≥32	2.4	3.1	94.5
aztreonam	≥256	≥256	0.03 to ≥256	2.6	0.1	97.3
piperacillin/tazobactam	≥256	≥256	64 to ≥256	0.0	0.0	100
doripenem	≥16	≥16	0.25 to ≥16	1.0	7.3	91.8
imipenem	≥16	≥16	1 to ≥16	3.5	32.7	63.7
meropenem	≥16	≥16	4 to ≥16	0.0	25.7	74.3
amikacin	8	≥64	≤0.25 to ≥64	52.3	12.1	35.6
colistind	0.5	≥16	≤0.06 to ≥16	69.4	—	30.6
tigecycline	1	2	0.12 to ≥16	79.9	14.3	5.8
levofloxacin	≥16	≥16	0.03 to ≥16	7.9	2.3	89.8
MBL positiveb (n=367)e
ceftazidime/avibactam	≥256	≥256	4 to ≥256	1.1	—	98.9
ceftazidime	≥256	≥256	32 to ≥256	0.0	0.0	100
cefepime	≥32	≥32	1 to ≥32	0.8	2.7	96.5
aztreonam	128	≥256	0.015 to ≥256	15.8	4.1	80.1
piperacillin/tazobactam	≥256	≥256	4 to ≥256	1.1	0.5	98.4
doripenem	≥16	≥16	2 to ≥16	0.0	1.1	98.9
imipenem	≥16	≥16	1 to ≥16	2.5	26.7	70.8
meropenem	≥16	≥16	4 to ≥16	0.0	26.4	73.6
amikacin	16	≥64	≤0.25 to ≥64	46.6	12.3	41.1
colistine	0.5	1	≤0.06 to ≥16	92.1	—	7.9
tigecycline	0.5	4	0.06 to ≥16	71.9	12.3	15.8
levofloxacin	≥16	≥16	0.03 to ≥16	9.3	6.3	84.5
Carbapenemase negative (MBL negative)c (n=98)f
ceftazidime/avibactam	1	4	0.12 to ≥256	95.9	—	4.1
ceftazidime	≥256	≥256	0.12 to ≥256	4.1	2.0	93.9
cefepime	≥32	≥32	0.25 to ≥32	4.1	4.1	91.8
aztreonam	≥256	≥256	0.06 to ≥256	4.1	2.0	93.9
piperacillin/tazobactam	≥256	≥256	2 to ≥256	4.1	0.0	95.9
doripenem	4	≥16	0.25 to ≥16	5.1	28.6	66.3
imipenem	4	≥16	0.25 to ≥16	49.0	27.6	23.5
meropenem	8	≥16	4 to ≥16	0.0	80.6	19.4
amikacin	8	≥64	0.5 to ≥64	61.2	12.2	26.5
colistinf	0.5	≥16	0.12 to ≥16	82.8	—	17.2
tigecycline	0.5	2	0.03–8	81.6	10.2	8.2
levofloxacin	≥16	≥16	0.06 to ≥16	15.3	7.1	77.6

MIC₅₀, MIC required to inhibit growth of 50% of isolates (mg/L); MIC₉₀, MIC required to inhibit growth of 90% of isolates (mg/L); S, susceptible; I, intermediate; R, resistant; —, no intermediate breakpoint.

^aIsolates tested positive for one or more of the serine carbapenemases tested (KPC, OXA-48 and GES) but negative for the MBL genes tested (IMP, VIM, NDM and SPM).

^bIsolates tested positive for one or more of the MBL genes tested (IMP, VIM, NDM, GIM and SPM).

^cIsolates tested negative for all carbapenemase genes tested (IMP, VIM, NDM, GIM, SPM, KPC, OXA-48 and GES).

^d–fIsolates with intrinsic resistance to colistin excluded (P. mirabilis, P. rettgeri, P. stuartii and S. marcescens)(number of isolates tested against colistin:

^d n=899;

^e n=329;

^f n=93).