Fruitbat

Biology 230

MIC Determination

BIOL 230 project BIOL 230 My home page

A broth dilution test is used to determine the minimal inhibitory concentration (MIC), the lowest concentration that prevents visible growth and the minimal lethal concentration (MLC). The MIC is determined by making a sequence of decreasing concentrations of the chemical in a broth, which is then inoculated with the test organism. The dilutions that do not show growth (higher concentration than the MIC) can be cultured in broth free of the drug. If growth occurs in this broth, the drug was not lethal, and the MIC can be determined.

 

Prepare serial dilutions of the antimicrobic in small sterile tubes, a cell well plate, or a Petrislide. A 2-fold dilution series is shown in the figure. Be sure to change pipette tips after each transfter and mix the contents of each well.

Add 2-5 ml of culture medium to each well and inoculate with the test organism; incubate.

.

Check the tubes or wells for growth. Here, growth is shown by a white dot in the bottom of the well. Record the presence of growth. You can determine the growth rate by plotting the number of cells against time.

Transfer an inoculum from wells showing no growth to new culture media. Incubate for 24 hr. and record the presence of growth.

If growth occurs in a subculture, the dilution was not lethal. The lowest dilution that inhibited growth is the MIC. The lowest dilution that killed the organisms (i.e., no growth in the subculture) is the minimum lethal concentration.

What is the MIC? The minimum lethal concentration?
Click here to check your answers.

If you do not reach the MIC or minimum lethal concentration, change the dilutions and try again.