Minimum Inhibitory Concentration (MIC) Testing Overview

Hi, I'm Sri Armugam, I'm the Director of Cell and Microbiology with Emery Pharma at Emory Pharma. We provide an area of microbiological services that can help test your compounds or medical devices against broad range of multi drug resistant strains of bacteria or fungi. Today we're going to speak about the minimum inhibitory concentration test, the MIC test.

Here at Emory Pharma we carry out MIC testing as per CLSI guidelines and this is a quick method and also.

A well approved method by most regulatory agencies.

MIC testing will be performed either in broth medium or agar medium is carried out in four steps. Step one is antimicrobial preparation. This can be done in two ways, macrodilution and microdilution. The macro dilution uses a larger volume where we use these tubes, whereas the microdilution is done in a 96 well plate format. So for today's demonstration I will be using a 96 well plate format. As you look at the plate, it has 12 columns. Column one would get the test article which is made at 2x concentration. And when you look at columns two to 11 these are used for two fold serial dilutions. We also use a growth control in column 12 as our negative control. And at the same time if you would like to compare your compound with a known antibiotic such as ciprofloxacin, we can use that as a positive control. Step two is inoculum preparation. Here I have a Staph aureus chain that I will be using as the test organism. This is a QC strain that I will be using to prepare for the bacterial inoculum of 0.5 McFallon Turbidity Standard verifying DOD by using a calorimeter. Step three is incubation of the antimicrobial agent with the respective bacteria. So the bacterial inoculum is added to the antimicrobial agent along with the growth media and it's incubated for a period.

Of 18 to 20 hours at 37 degrees Celsius. Step four, which is the final step, is visualizing the mic value. As you can see, we use a mirror reader which helps us to carefully examine each well for visible bacterial growth. As you can see, column 12 is the growth control where you see turbidity, whereas column number six is actually the MIC for this compound because this is a clear well and has no growth. And this is also further confirmed by reading the absorbance values using a spectrophotometer.