Question

What is Minimak Inhibitory Concentration (MIC)
Then Name and Describe 2 methods for determining MIC

Answer 1

Answer:

• MIC- The Minimal Inhibitory Concentration or MIC is the lowest concentration of the test substance(drug, antibiotic, etc.), that is required to inhibit the growth of the target organism, in vitro, after subsequent incubation.
  
• The name of two methods of determining MIC are 1) Determining MIC by the zone of inhibition method and 2) The broth dilution method.
  

Determining MIC by the zone of Inhibition:

• In this method, a standardized volume of the suspension of the organism is prepared and a stock solution of the test drug is prepared.
• The drug is serially diluted in different dilutions.
• the suspension of the organism is plated on the surface of media plates and "wells" were prepared in triplicate in each media plate.
• Each dilution is poured in respective plates(wells) and the drug solutions are added in a low to a high concentration. i.e. the first agar plate containing the highest dilution and the last agar plate containing the lowest dilution.
• Then the plates are kept in incubation
• After incubation, the visible zone of inhibition is observed.
• The MIC is in between the dilution for which there is no visible zone of inhibition and the dilution which produced the first visible zone.
• note: higher dilution means a lower concentration of drug and vice versa.

​​​​​​​​​​The broth dilution method:

• ​​​​​​​At first, the drug to be tested is taken and a stock solution of the drug is prepared.
• Then the drug is serially diluted from the stock solution.
• several broth dilution tubes were taken in which each tube contains a particular dilution of the test drug.
• the tubes are placed in order of lowest to the highest concentration of the test drug and the same standardized volume of an organism is added in each tube and then put it under incubation.
• After incubation identify the tube where no visible growth is found(spectrophotometrically or visibly).
• Then the Minimal Inhibitory Concentration is in between the last concentration where growth was found and the first concentration where there is no growth.
• The lower the MIC the better the drug to be applicable.