Minimum Inhibitory concentration of antibiotic << Back

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Introduction

Lowest concentration which will inhibit the visible growth of microbes is Minimum inhibitory concentration (MIC) for antibiotics. It is important in labs dealing with clinical testing confirming the microbial resistance to an antimicrobial mediator/agent. The lower the minimum inhibitory concentration the more well is the antimicrobial compound.

Principles

The Minimum Inhibitory Concentration (MIC) analysis is a technique used for determination of lowest concentration of any antimicrobial compound needed for inhibition of microbes. This method is routinely performed in the labs for determination of microbial resistance to the antimicrobial compound/agent. 

 

Materials

Ø  Activated cultures of bacteria

Ø  Autoclaved petri dishes

Ø  diluents (sterile)

Ø  Test tubes

Ø  Growth media plates

Ø  Growth medium broth

Ø  Inoculating loop

Ø  Autoclave

Ø  Cup borer

Ø  Incubator

Procedure

Ø  Autoclave the growth media for the activation of microbe. In case of mesophlic bacteria nutrient broth will be used and for fungi potato dextrose broth will be used.

Ø  In the growth media inoculate the organism and measure the growth of organism till it comes in the lag phase by taking O.D. at 660nm.

Ø  Pour the agar growth media inoculated previously with organism in the aseptic conditions. Allow it to solidify.

Ø  Decide the concentrations of microbial agent for antimicrobial test and using suitable diluent prepare the exact concentration of antimicrobial compound.

Ø  Red hot the cup borer and punch the agar plates by cup borer.

Ø  Inoculate the compounds in the well made by the cup borer.

Ø  Allow to stay for 2-3 mins for proper diffusion of compounds in the well.

Ø  Incubate in the incubator for 24 hours at microbe growth temperature.

Ø  Measure the zone of inhibition.

Procedure for determination of MIC using broth medium

Ø  Prepare the serial dilution of antibiotics having different concentration of antibiotics in separate test tubes.

Ø  Inoculate in the same test tubes with the microbial culture.

Ø  Tubes are then incubated in the incubator. Tubes that show growth/turbidity indicates the bacterial growth and the inhibition of microbe will be seen in the tubes having clear medium.

Advantages

Ø  Easy to handle

Ø  Precise test for knowing antibiotic sensitivity/resistance

Ø  Commonly used and accepted procedure

Disadvantages

Ø  Not used for screening/evaluating new compounds.

 

Reference books:

  • Principles of Microbiology By Atlas R.M.: 2nd edition
  • Microbiology by Pelczar M.J. & Chain E.C.S. : 5th edition
  • Microbiology by Prescott L.M.
  • International student edition: Microbiology- A laboratory Manual 4th edition. By James G. Chappuccino & Natalie Sherman
  • A Text Book of Microbiology, 3rd ed, - R.C Dubey and D. K Maheshwari -S. Chand and Company.
  • General Microbiology ( Vol I & II) 3rd ed,- C.B Powar and H.F Daginawala-  Himalaya Publishing House.
  • General Microbiology, 5thed, Macmilan Press ltd.- Stanier R.