Table 1.

CLSI/EUCAST Breakpoints for Colistin

	Colistin MIC, mg/L
Organism	Susceptible	Intermediate	Resistant
CLSIa
Acinetobacter sp	≤ 2	-	≥ 4
Pseudomonas	≤ 2	-	≥ 4
aeruginosa
EUCAST
Acinetobacter sp	≤ 2		> 2
P. aeruginosa	≤ 2		> 2
Enterobacteriaceae	≤ 2		> 2

CLSI = Clinical and Laboratory Standards Institute; EUCAST = European Committee on Antimicrobial Susceptibility Testing; MIC = minimum inhibitory concentration.

^aFor isolates of Enterobacter aerogenes, Enterobacter cloacae, Escherichia coli, Klebsiella pneumoniae, and Raoultella ornithinolytica, CLSI define insufficient clinical and pharmacokinetic/pharmacodynamic (PK/PD) data to set a PK/PD-based breakpoint and cite epidemiological cutoff values (ECVs) of 2 mg/L based on MIC distribution data.^{11, 12}