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

Table 2

Joint EUCAST-CLSI recommendations on colistin susceptibility testing.

Reference method	Broth microdilution
Preparation according to ISO 20776-1 standard [102]	(i) Cation-adjusted Mueller-Hinton medium (MH2)
	(ii) Colistin sulfate
	(iii) Polystyrene trays without pretreatment
	(iv) Absence of polysorbate 80 or any surfactant
MIC breakpoint (µg/ml)	Enterobacteriaceae	P. aeruginosa	Acinetobacter spp.
EUCAST [100]	S ≤ 2 and R > 2	S ≤ 2 and R > 2	S ≤ 2 and R > 2
CLSI [103]	ECV: WT ≤ 2 and NWT ≥4	S ≤ 2 and R ≥ 4	S ≤ 2 and R ≥ 4
Quality control [104] (µg/ml)	E. coli ATCC 25922	P. aeruginosa ATCC 27853	E. coli (mcr-1) NCTC 18853^#
Target	0.5–1	1–2	4
Range	0.25–2	0.5–4	2–8

Epidemiological cutoff values: clinical data and PK/PD are not sufficient to evaluate a clinical breakpoint for the following species: E. aerogenes, E. cloacae, E. coli, K. pneumoniae, and R. ornithinolytica. WT: wild type; NWT: non-wild type. ^#Recommended by EUCAST; MIC must be 4 µg/ml and only occasionally 2 or 8 µg/ml.