Minimum Inhibitory Concentration (MIC) is the lowest concentration of an antibiotic (in mg/L) that visibly inhibits growth of a microorganism after overnight incubation. Lower MIC values indicate greater antibiotic potency against that organism.

What is the difference between EUCAST and CLSI breakpoints?

EUCAST (European Committee on Antimicrobial Susceptibility Testing) and CLSI (Clinical and Laboratory Standards Institute) are two independent standard-setting bodies. They use similar but not identical epidemiological and PK/PD data, so breakpoints can differ. EUCAST is predominant in Europe; CLSI in North America.

What does Intermediate (I) mean?

Under EUCAST, "I" was redefined in 2019 as "Susceptible, Increased Exposure" — meaning the organism may be treated at a higher dose or if the infection site achieves high drug concentrations. Under CLSI, Intermediate indicates a buffer zone where minor technical factors could cause a major interpretive error.

Are these breakpoints up to date?

Breakpoints in this tool reflect EUCAST v14 (2024) and CLSI M100 Ed34 (2024) for illustrative common combinations. Always consult the latest official documents from eucast.org or clsi.org for clinical decision-making.

What if my organism/antibiotic combination is not listed?

This tool covers the most frequently tested combinations. For unlisted combinations, consult EUCAST or CLSI tables directly, or use species-specific breakpoints from the relevant document section.

Can I use this tool for clinical decisions?

This tool is for educational and verification purposes only. All clinical susceptibility interpretations should be performed by accredited laboratories following their validated procedures and the most current published guidelines.

MIC Interpretation Tool

Name: MIC Interpretation Tool
Availability: InStock
Author: Nham Vu

Enter a Minimum Inhibitory Concentration (MIC) value, select an organism and antibiotic, and get an instant Susceptible / Intermediate / Resistant classification based on EUCAST and CLSI breakpoints.

MIC Input

Guideline

Organism

Antibiotic

MIC Value (mg/L)

Common dilutions: 0.016, 0.03, 0.06, 0.125, 0.25, 0.5, 1, 2, 4, 8, 16, 32, 64

Select organism, antibiotic, and enter a MIC value to see the interpretation

Breakpoints for Selected Combination

Guideline	S ≤ (mg/L)	I (mg/L)	R ≥ (mg/L)
Select organism and antibiotic above

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Summary

Enter a Minimum Inhibitory Concentration (MIC) value, select an organism and antibiotic, and get an instant Susceptible / Intermediate / Resistant classification based on EUCAST and CLSI breakpoints.

How it works

Select the guideline: EUCAST (v14, 2024) or CLSI (M100 Ed34, 2024).
Choose the organism and antibiotic from the lists.
Enter the measured MIC value in mg/L.
The tool compares it to the stored S and R breakpoints: MIC ≤ S breakpoint → Susceptible; MIC ≥ R breakpoint → Resistant; values in between → Intermediate.
Review the displayed breakpoints to trace the result back to the published source.

Use cases

Interpret MIC results from broth microdilution panels in clinical microbiology labs.
Cross-check automated susceptibility system calls against published breakpoints.
Teach antimicrobial susceptibility testing interpretation in microbiology courses.
Verify appropriate antibiotic selection during antimicrobial stewardship reviews.
Quick reference during ward rounds when pharmacy or lab data is not immediately available.

Frequently Asked Questions

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Last updated: 2026-05-23 · Reviewed by Nham Vu