The minimum inhibitory concentration (MIC) test determines the lowest amount of a compound that limits visible microbial growth in culture. It can provide important information about the susceptibility of microorganisms to drugs used to treat infections. Technicians create a standardized and controlled dilution of the test compound and add it to agar or broth plates with the test organism. The test can be used in individual susceptibility assessments and pharmaceutical research. Testing is relatively easy and quick, and laboratories use controls to reduce error rates.
The minimum inhibitory concentration (MIC) is the lowest amount of a compound that limits visible microbial growth in culture. The lower the number, the more effective the agent against microorganisms. MIC tests can provide important information about the susceptibility of certain organisms, such as bacteria and fungi, to drugs used to treat infections. It is typically done in a laboratory setting and requires overnight for the culture to grow.
In this test, a technician creates a standardized and controlled dilution of the test compound and adds it to agar or broth plates with the test organism. The mixture is incubated overnight and then evaluated in the morning. If the organisms are growing, that means the concentration isn’t high enough. If there is no visible growth, the compound works. By testing a range of concentrations, technicians can reset the minimum inhibitory concentration to zero.
One use for this test is in individual susceptibility assessments. A patient with an infection that does not respond to initial treatment or is likely to be resistant may be asked to provide a sample for culture purposes. In the lab, a technician can find out which antimicrobial drugs will work and can make a dosage recommendation. Over time, this data can lead to revisions to prescribing guidelines as technologists find the range where agents are effective with the lowest side effects.
It is also possible to use minimal inhibitory concentration tests in pharmaceutical research. Pharmaceutical companies want to know which organisms a drug can treat and how much drug is needed to get a positive result. Such research can also be used to explore natural compounds historically used to treat infections, such as tea tree oil, which is known to have antimicrobial properties. The outcome of the minimal inhibitory concentration test can be used to guide dosing for clinical trials.
Testing can be quick, as labs typically only require overnight to process the sample. It’s also relatively easy and provides a wealth of data for care providers and researchers. Laboratories use a variety of controls to reduce error rates with minimum inhibitory concentration testing and other procedures. They can repeat and randomly check tests, for example, to make sure the results are accurate. Suspicious results can also be automatically flagged for re-testing to confirm before being passed on to the scientist or health care provider who requested the test.
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