Canadian Journal of Infectious Diseases and Medical Microbiology

Review Article

Development of New Tools to Detect Colistin-Resistance among Enterobacteriaceae Strains

Table 3

Comparison of different colistin susceptibility testing methods to detect colistin resistance in Gram-negative clinical isolates.


Bacterial species	Reference method	MIC breakpoint	MIC range; % resistant	MIC50 (µg/ml)	MIC90 (µg/ml)	Methods	CA ≥ 90%	EA ≥ 90%	ME ≤ 3%	VME ≤3%	MiE	References

42 A. baumannii isolates	BMD	S ≤ 2 µg/ml	0.5–4 µg/ml	1 µg/ml	2 µg/ml	BMD in glass-coated plates	92.8	100	0	100		[114]
		S ≤ 2 µg/ml	0.5–4 µg/ml			AD	78.5	92.8	15.4	100
		R > 2 µg/ml	0.07%			E-test	92.8	16.6	0	100
		R > 2 µg/ml	0.07%			Vitek 2² AST-N2812	92.8	61.9	0	100

353 isolates	BMD	S ≤ 2 µg/ml	ND	ND	ND	Sensitest	98.9	96	1.46	0.93		[146]
(83 mcr-1)	BMD	R > 2 µg/ml	38.8%	ND	ND	Sensitest	98.9	96	1.46	0.93		[146]

219 isolates		S ≤ 2 µg/ml	ND	ND	ND	Phoenix 100³ NMIC-417	96.8	ND	0.6	10		[146]
219 isolates		R > 2 µg/ml	27.4%	ND	ND	Phoenix 100³ NMIC-417	96.8	ND	0.6	10		[146]

14 E. coli isolates	BMD	S ≤ 2 µg/ml	0.25–128 µg/ml; 48%	2	16	Sensititre¹ SEMPA1	94.7	96	10.2	0		[143]
18 K. pneumoniae isolates		R > 2 µg/ml				Micronaut-S	89.3	96	15.4	5.6
21 P. aeruginosa isolates						Micronaut-MIC	90.7	99	12.8	5.6
22 Acinetobacter spp. isolates						Etest, Oxoid MH	81.3	71	5.1	33.3
						Etest, BBL MH	78.7	43	2.6	41.7
						Etest, MHE	85.3	47	5.1	25
						MTS, Oxoid MH	78.7	40	0	44.4
						MTS, BBL MH	76	49	0	50
						Sensitest	89.3	88	17.9	2.8
						UMIC	92	82	7.7	8.3

117 A. baumannii isolates	BMD	S ≤ 2 µg/ml	≤0.5–≥16 µg/ml; 24.8%	≤0.5	8	Vitek 2 AST-XN05	89.7	88.9	1.1	37.9		[129]
		R > 2 µg/ml				Phoenix 100 NMIC/ID-96	88.9	91.5	1.1	41.4
						AD	87.2	93.2	15.9	3.4

123 Enterobacteriaceae isolates (14 mcr-1 and 1 mcr-2)	BMD	S ≤ 2 µg/ml	0.12–128 µg/ml; 67.5%			Phoenix 100 NMIC-93	91.8	ND	0	12.1		[83]
		R > 2 µg/ml				Rapid NP	98.3	NA	2.5	1.2

15 Hafnia alvei isolates	BMD	S ≤ 2 µg/ml	0.125–32 µg/ml; 96%	8	16	DD	4	NA	0	100		[79]
10 Hafnia paralvei isolates		R >2 µg/ml		8	8	Etest	76	32	0	25
						Phoenix NMIC-93	100	NA	0	0
						Rapid NP	100	NA	0	0

76 Enterobacteriaceae isolates (21 mcr-1)	BMD	S ≤ 2 µg/ml	0.06–>64 µg/ml; 32.9%	0.25	16	Vitek 2 AST N315	88.2	93.9	0	36		[147]
		R >2 µg/ml		2 (4)	8 (8)	Sensititre GNX3F	90.1	89.5	11.8	4
				0.12	0.5	Etest	92.1	75	5.9	12
						MicroScan⁴ NM44	88.2	NA	15.8	4

246 isolates (absence of mcr genes)	Broth macrodilution	S ≤ 2 µg/ml	≤0.5–>8 µg/ml; 12.6%	≤0.5	8	Etest	95.1	92.3	0.4	35.5		[160]
		R >2 µg/ml

41 K. pneumoniae isolates	BMD	S ≤ 2 µg/ml	2–>128 µg/ml; 95.1%	8	32	BMD-P80	82	95.1	0	18.9	NA	[110]
20 A. baumannii isolates		R > 2µg/ml		8	32	AD	91.8	55.7	100	3.4
						Etest	59	50.8	33.3	39.3
						MTS	67.2	65.6	33.3	41.4
						Vitek 2 AST EXN8	96.7	70	66.6	0

290 A. baumannii isolates	BMD	S ≤ 2 µg/ml	1–128 µg/ml; 9.3%	2	2	DD 10 µg (9–12 mm)	94.8	NA	0	0	5.2	[136]
		R > 2 µg/ml				Etest S ≤ 2; R > 4	94.5	2.1	0	55.5	0
						Etest S ≤ 0.5; R > 2	99.3	≡	0	0	5.5
						Vitek 2 AST-N136	94.1	44.8	0.38	59.2

213 Acinetobacter sp. isolates	AD	S ≤ 2 µg/ml	≤0.5–≥32 µg/ml; 6.1%	1	2	Vitek 2 AST-N132	99.1	ND	0	15.4		[115]
		R >2 µg/ml				Etest	87.3		1	0
						MicroScan panel type 42	99.1		12.5	15.4

60 P. aeruginosa isolates	BMD-P80	S ≤ 2 µg/ml	≤0.12–≥8 µg/ml; 17.8%			Broth macrodilution	98	83	2.3	0		[128]
20 K. pneumoniae isolates		R >2 µg/ml			>8	Etest	91	61	4.5	31.6
27 A. baumannii isolates					>8

11 A. baumannii isolates	BMD-P80	S ≤ 2 µg/ml	≤0.12–≥8 µg/ml; 20%		>8	BMD	88	34	12.5	10		[128]
15 K. pneumoniae isolates		R >2 µg/ml			>8	AD	94	80	7.5	0
24 P. aeruginosa isolates						Sensititre GNXF	96	62	5	0

11 A. baumannii isolates	BMD-P80	S ≤ 2 µg/ml	≤0.12–≥8 µg/ml; 30%			Etest, BBL MH	78	46	5.7	47		[128]
15 K. pneumoniae isolates		R > 2 µg/ml				Etest, Hardy MH	78	64	2.8	53
24 P. aeruginosa isolates					>8	Etest, Remel MH	84	68	2.8	47

109 P. aeruginosa isolates	BMD	S ≤ 2 µg/ml	0%			Phoenix NMIC/ID-76	100	99.1	0	0		[149]
		R >2 µg/ml

63 E. coli isolates	BMD	S ≤ 2 µg/ml	0.12–16 µg/ml; 18.6%		1	BMD-P80	99.2	41.3	0	43.5		[112]
61 K. pneumoniae isolates		R >2 µg/ml			0.5
60 Acinetobacter spp. isolates					2
63 P. aeruginosa isolates					2

200 Enterobacteriaceae isolates	AD	S ≤ 2 µg/ml	0.128–>128 µg/ml; 28.5%			DD 50 µg; R < 15 mm	96.5	NA	0	12.3		[116]
82 K. pneumoniae isolates		R > 2 µg/ml		0.5	128	DD 10 µg; R ≤ 8; S ≥ 11 mm	93	NA	0	8.8	4.5
51 E. coli isolates				0.5	0.5	DD 10 µg; R ≤ 11; S ≥ 14 mm	99.5	NA	0	1.7	26.5
67 E. cloacae isolates				0.5	2	Etest	100	52	0	0	0

25 P. aeruginosa isolates	AD	S ≤ 2 µg/ml	0.25–≥256 µg/ml; 57.1%	2	>256	BMD	81.1	40.5	0	25	5.4	[120]
12 S. maltophilia isolates		R > 4 µg/ml		>256	>256	Etest	74.3	56.7	0	35	11.4
						DD 10 µg; R ≤ 10; S ≥ 11 mm	82.8	NA	0	35	2.9

157 E. coli isolates	AD	S ≤ 2 µg/ml	0.25–32 µg/ml; 9.6%	0.5	2	DD 150 µg; R < 16; S ≥ 20 mm	46.5	NA	1.4	20	49.7	[123]
		R >4 µg/ml				DD 10 µg; 2 + 18H (10–15)	96.8	NA	0.7	13.3	1.9
						Etest	96.8	81.5	0.7	0	0.6

78 P. aeruginosa isolates	BMD	S ≤ 2 µg/ml	<0.25–2 µg/ml; 0	1	1	Etest	100	79.5	0	0	6.4	[135]
		R > 4 µg/ml				DD 10 µg	100	NA

100 A. baumannii isolates	Phoenix	S ≤ 2 µg/ml		0.5	0.5	DD 10 µg; R ≤ 8; S ≥ 11 mm	100	NA	0	0		[137]
		R > 4 µg/ml				Etest	100	NA	0	0

154 Acinetobacter spp. isolates	AD	S ≤ 2 µg/ml	≤0.064–≥32; 11.7%	NA	NA	Etest	98.7	88	0.7	5.6		[124]
		R ≥ 4 µg/ml

170 Gram-negative isolates	AD	S ≤ 4 µg/ml	0.25–128; 31.2%			Etest	100	91.2	0	0		[126]
		R > 4 µg/ml

102 Gram-negative isolates	BMD	S ≤ 2 µg/ml	<0.5–>64 µg/ml; 50%	NA	NA	AD, Oxoid MH	ND	96.8				[31]
		R > 4 µg/ml				AD, Oxoid Iso-Sensitest		97.9
						Etest, MH		72.6
						Etest, ISO		64.2
						Vitek 2 AST N038		93.1
						DD 10 µg; R ≤ 10; S ≥ 13 mm		NA

44 Acinetobacter spp. isolates	AD	S ≤ 2 µg/ml	1-2 µg/ml; 0	1	2	Vitek 2 AST-N032	100	ND	0	NA	NA	[118]
		R > 2 µg/ml

172 Gram-negative isolates	AD	S ≤ 2 µg/ml	0.5–64; 31.4%			Vitek 22 AST-N032 (n = 32)	82	75.2	0	57.4		[32]
		R > 2 µg/ml				Etest (n = 137)	86.6	75.0	6.8	27.8

115 A. baumannii isolates	BMD	S ≤ 2 µg/ml	≤0.06–512 µg/ml; 19.1%	≤0.06	32	Etest	98.2	16.5	0	1.7		[138]
		R > 2 µg/ml

501 P. aeruginosa isolates (401 CF)	AD	S ≤ 4 µg/ml	≤0.5–≥16 µg/ml; 17.8%	2	4	BMD 24 h	96		1.2	26.5		[121]
50 A. xylosoxidans isolates		R >4 µg/ml		4	≥16	BMD 48 h	93.6		3.9	18.0
50 S. maltophilia isolates				8	≥16

70 S. maltophilia	AD	S ≤ 2 µg/ml	0.12–32 µg/ml; 24.3%	2	4	DD 10 µg; R ≤ 8; S ≥ 11 mm	71.2	NA	0	93.7	5.7	[125]
		R > 2 µg/ml				Etest	86.4	96.7	5.6	37.5	NA

200 Gram-negative isolates	BMD	S ≤ 2 µg/ml	≤1–>128 µg/ml; 15%			DD 10 µg; R ≤ 10; S ≥ 14 mm	94	NA	0	21.8	1.5	[127]
(i) 60 A. baumannii isolates		R > 2 µg/ml		≤1	2	DD 10 µg; R ≤ 8; S ≥ 11 mm	95		0	31.2	1
(ii) 80 P. aeruginosa isolates				≤1	≤1
(iii) 12 S. maltophilia isolates				≤1	32

35 representatives	BMD	S ≤ 2 µg/ml	≤1–≥128 µg/ml; 40%			AD	97.1	91.4	47.6	0		[127]
		R > 2 µg/ml

CA: categorical agreement; EA: essential agreement; VME: very major error; ME: major error; MiE: minor error; AD: agar dilution; BMD: broth microdilution; DD: disk diffusion; MH: Mueller-Hinton. Italic values indicate the number of errors and not the percentage when a too few number of strains tested, where R for VME or S for ME. ¹Sensititre panels: ≤0.25–>4 µg/ml except for SEMPA1. ²Vitek 2 reagent cards: ≤0.5–≥16 µg/ml except for AST-N038 (≤2, 4, and >4 µg/ml) and AST-N032 (1–4 µg/ml). ³Phoenix 100 cards: ≤1–>4 µg/ml. ⁴MicroScan-dried Gram-negative breakpoint combo panel type 42 ≤2 and >4 µg/ml. Prediffusion test: discs were removed after 2 h of incubation.