Reference Antimicrobial Susceptibility Testing (AST) Data

At a glance

Access downloadable distributions of minimum inhibitory concentration (MIC) for bacteria and fungi.


CDC programs perform AST of bacterial and bloodstream Candida isolates collected in surveillance programs and isolates submitted to CDC from the reference laboratories for susceptibility testing because of unusual resistance. CDC laboratories default method is broth microdilution using frozen in-house prepared panels according to standards established by the Clinical and Laboratory Standards Institute (CLSI Documents: M7 for bacteria; M27 with M60 for Candida). Etest is a reference method for antifungal susceptibility to amphotericin B in accordance with CLSI M-27e4. CDC is making these data available online for use in setting breakpoints for interpretation of antimicrobial susceptibility testing.

The downloadable data contain tables and graphic representations that display minimum inhibitory concentration (MIC) distributions for various bacteria and Candida. We provide a description of the isolates tested with each dataset. CDC will continue to expand this database to include data from additional bacterial and fungal isolates and data from new antimicrobial drugs.

MIC data for Neisseria gonorrhoeae isolates can be found on the CDC Division of STD Prevention (DSTDP) Gonococcal Isolate Surveillance Project (GISP) Profiles and Annual Reports.

Downloadable Data & Additional Information

Distributions of MIC for bacteria

Distributions of MIC for fungi

Additional Information

Supplemental information: interpretation rules for MIC values for bacterial pathogens

Lower range MIC (mcg/ml)

Lower range MIC (mcg/ml)
LIMS MIC value (as entered) MIC Distribution Interpretation
0.059 ≤ 0.06
0.119 ≤ 0.12
0.249 ≤ 0.25
0.49 ≤ 0.5
0.9 ≤ 1
1.9 ≤ 2
3.9 ≤ 4

Higher range MIC (mcg/ml)

Higher range MIC (mcg/ml) 
LIMS MIC value (as entered) MIC Distribution Interpretation
4.1 ≥ 8
8.1 ≥ 16
17 ≥ 32
33 ≥ 64
65 ≥ 128
129 ≥ 256
257 ≥ 512
513 ≥ 1024

Not-determined MIC

If the MIC values are not available or not determined within the they will appear in the dataset as one of these:

  • "ND"
  • A blank cell
  • A single period "."

If any of the above appear in the dataset, they should be interpreted as "not determined."

Clinical specimen terms

Terms that require decoding: BAL = Bronchoalveolar lavage