Determination of MIC by Agar Diffusion Method

Minimum Inhibitory Concentration (MIC)

Definition: is the lowest concentration of an antimicrobial agent that will inhibit the visible growth of a microorganism after overnight incubation.

WHY?Clinically, MIC is not only used to determine the amount of antibiotic that the patient will receive but also the type of antibiotic used. This will lower the opportunity for microbial resistance to specific antimicrobial agents.

Common methods used for MIC determination

MIC by broth dilution method MIC by agar diffusion method

MIC by agar diffusion method Principle

Different gradient of AB solution Inoculation with the isolated pathogenic

microorganism Incubation for 24 hour Observation of the diameter of the zone of

inhibition as a parameter of the growth

Principle

Principle (Cont.)

Detailed procedure Materials:

Nutrient agar tube Sterile Petri dish Test tube with bacterial culture 2 sterile Pasteur pipettes Sterile Cork borer Sterile blade 4 Wassermann tubes with 4 different

concentrations of antibiotic

Detailed procedure

Precautions Pour the agar at optimum temp. (< 50oC)

Mix very well

Flame the blade very well after and before each cup

Don’t leave any agar debris inside the cup

Transfer the antibiotic from the low to the high concentration

AVIOD THE OVERFLOW

!!DO NOT INVERT THE PLAT!! Transfer the plate very carefully

Expected results

Results

Antibiotic Concentration µg/ml

Log concentration

Zone Diameter (mm)

100217

2502.3920

7502.8724

30003.430

Zone Diameter (mm)

Log ConcLog MIC

Results

Zone Diameter (mm)

Log ConcLog MIC

Results