. 2020 Nov 11;34(1):e00115-20. doi: 10.1128/CMR.00115-20

TABLE 2.

Breakpoints for interpretation of MICs and zone diameters approved by EUCAST (version 10.0, valid from January 2020), FDA, and CLSI (M100 30th edition, valid from January 2020)^a

Antibiotic(s)	EUCAST						FDA						CLSI
	MIC (mg/liter)			Zone diameter (mm)			MIC (mg/liter)			Zone diameter (mm)			MIC (mg/liter)			Zone diameter (mm)
	S	I	R	S	I	R	S	I	R	S	I	R	S	I	R	S	I	R
CAZ-AVI for zone diameter breakpoints, disk content 10/4 μg (EUCAST), 30/20 μg/ml (CLSI/FDA)
Enterobacterales	≤8^b		>8^b	13		13	M100^c						≤8/4		≥16/4	≥21^d		≤20^c
P. aeruginosa	8^b		8^b	17		17	M100						≤8/4		≥16/4	≥21		≤20
TOL-TAZ for zone diameter breakpoints, disk content 30/10 μg/ml (EUCAST/FDA/CLSI)
Enterobacterales	≤2^e		>2^e	22		22	M100			>22	19–21	<18	≤2/4	4/4	≥8/4	≥21	18–20	≤17
P. aeruginosa	≤4^e		>4^e	24		24	M100						≤4/4	8/4	≥16/4	≥21	17–20	≤16
Haemophilus influenzae (pneumonia)	≤0.5^e		>0.5^e	IP		IP	≤0.5/4
Streptococcus viridans group	IE		IE	IE		IE	M100						≤8/4	16/4	≥32/4
Bacteroides fragilis							≤8/4	16/4	≥32/4
MER-VAB for zone diameter breakpoints, disk content 20/10 μg/ml (CLSI/FDA)
Enterobacterales	≤8^f		>8^f	IP		IP	M100						≤4/8	8/8	≥16/8	≥18	15–17	≤14
P. aeruginosa	8^f		8^f	IP		IP
IMI-REL for zone diameter breakpoints, disk content 10/25 μg/ml (FDA)
Enterobacterales^g	≤2^h		>2^h	IP		IP	≤1/4	2/4	≥4/4	≥25	21–24	≤20
P. aeruginosa	≤2^h		>2^h	IP		IP	≤2/4	4/4	≥8/4	≥23	20–22	≤19
Acinetobacter spp.	≤2^h		>2^h	IP		IP
Viridans group streptococci	≤2^h		>2^h	IP		IP
Gram-positive anaerobes	≤2^h		>2^h				≤4/4ⁱ	8/4ⁱ	≥16/4ⁱ
Gram-negative anaerobes	≤2^h		>2^h				≤4/4ⁱ	8/4ⁱ	≥16/4ⁱ

CAZ-AVI, ceftazidime/avibactam; TOL-TAZ, ceftolozane/tazobactam; MER-VAB, meropenem/vaborbactam; IMI-REL, imipenem/relebactam; IP, in preparation; IE, insufficient evidence. The respective dosages for each β-lactam/β-lactamase inhibitor are shown in Table 3.

For susceptibility testing purposes, the concentration of avibactam is fixed at 4 mg/liter.

M100 standard is recognized.

Confirmatory MIC testing is indicated for isolates with zones of 20 to 22 mm to avoid reporting false-susceptible or false-resistant results.

For susceptibility testing purposes, the concentration of tazobactam is fixed at 4 mg/liter.

For susceptibility testing purposes, the concentration of vaborbactam is fixed at 8 mg/liter.

EUCAST-approved breakpoints for Enterobacteriales, except Morganella spp.; FDA-approved breakpoints for Enterobacteriaceae: clinical efficacy was shown for Klebsiella aerogenes, Enterobacter cloacae, Escherichia coli, Klebsiella pneumoniae, Citrobacter freundii, and Klebsiella oxytoca.

For susceptibility testing purposes, the concentration of relebactam is fixed at 4 mg/liter.

ⁱ

FDA-approved breakpoints for anaerobes using agar dilution method, clinical efficacy shown for Bacteroides caccae, Bacteroides fragilis, Bacteroides ovatus, Bacteroides stercoris, Bacteroides thetaiotaomicron, Fusobacterium nucleatum, and Parabacteroides distasonis.