University of Pennsylvania Medical Center Guidelines
for Antibiotic Use
Measurement of MIC
The minimum inhibitory concentration or MIC is defined as the
minimum concentration of antibiotic which will inhibit the growth of
the isolated microorganism . There are many ways to measure the MIC,
including:
- Broth dilution
- Agar dilution
- E-test
An example of the broth dilution test is shown below.
This figure shows a schematic of the broth dilution test.
Bacteria are inoculated into tubes containing culture broth and
varying concentrations of the antibiotic to be tested. The tubes are
incubated to allow bacterial growth. The MIC is read as the lowest
concentration of antibiotic which inhibited bacterial growth. In the
above example, the MIC would be 8 micrograms/ml. The interpretation
of this MIC depends on the organism/antibiotic pair being tested, and
is made following standard NCCLS
guidelines.
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