MIC test microbiology principle, procedure

The MIC test microbiology (Minimal Inhibitory Concentration) test is a fundamental laboratory method used to determine the lowest concentration of an antimicrobial agent required to inhibit the growth of a specific microorganism.

Mic tests are especially crucial in guiding treatment decisions, antibiotic development, and antibiotic stewardship program

Method and Material’s for Mic test

• Microbial culture: You’ll need a pure culture of the microorganism you want to test.
• Mueller-Hinton agar: This is a standard growth medium for bacterial culture.
• Antibiotics or antimicrobial agents: The ones you wish to test.

• Sterile Petri dishes or microtiter plates: These will hold the agar and microbial culture.
• Inoculating loops or swabs: To transfer the microorganism to the agar plates.
• Incubator: To maintain a controlled temperature for microbial growth.
• Spectrophotometer or turbidimeter (optional): For automated measurements.

MIC test procedure in microbiology

1. Preparation of Inoculum:

• Start with a fresh microbial culture. Ensure it is in the logarithmic growth phase for accurate results.
• Adjust the microbial suspension to a specific turbidity. This can be done visually by comparing it to the McFarland Standard, or more precisely, using a spectrophotometer or turbidimeter.

1. Inoculation of Agar Plates:

• Pour the Mueller-Hinton agar into Petri dishes or distribute it into microtiter wells.
• Once the agar has solidified, use an inoculating loop or swab to streak the inoculum evenly on the surface of the agar.

1. Application of Antibiotics:

• Prepare dilutions of the antibiotics or antimicrobial agents you want to test. These should cover a range of concentrations.
• Apply a specific volume of each dilution to the surface of the inoculated agar plates or wells.

1. Incubation:

• Incubate the plates or microtiter plates at the appropriate temperature (usually 35°C) for a defined period, typically 18-24 hours.

1. Reading the Results:

• After incubation, examine the plates or wells for visible growth.
• The Mic is the lowest concentration of the antibiotic at which there is no visible growth. This is usually the lowest concentration where the microbial growth appears significantly inhibited compared to the control plate without antibiotics.

1. Recording Mic Values:

• Record the Mic values for each antibiotic tested.