Minimum Inhibitory Concentration (MIC),
Minimum Bactericidal Concentration (MBC),
and Minimum Fungicidal Concentration (MFC)

In microbiology, the Minimum Inhibitory Concentration (MIC) is a test that determines the lowest concentration of a antimicrobial agent needed to inhibit the visible in-vitro growth of a challenge microorganism.  To establish the MIC, an antimicrobial agent is incubated across a dilution range with the challenge microorganism typically at a suspension concentration of one million colony forming units (CFU) per milliliter (mL).  Growth of the microorganism is determined by turbidity.  Test samples exhibiting no antimicrobial activity will be turbid (i.e., cloudy) due to the presence of the microorganism whereas the lack of turbidity indicates that the growth of the challenge microorganism has been inhibited. Once the MIC of an antimicrobial agent is calculated, microorganisms are labeled as susceptible, susceptible-dose dependent (SSD), intermediate, or resistant to the antimicrobial agent.

The MIC test is often taken one step further to determine the Minimum Bactericidal Concentration (MBC) and Minimum Fungicidal Concentration (MFC) of agents. The MBC and MFC refers to the minimum concentration of an antimicrobial agent that reduces the viability of the initial microorganism inoculation by ≥99.9%. In contrast to the MIC that establishes the lowest concentration of antimicrobial agent that inhibits growth, the MBC and MFC identify the lowest concentration of antimicrobial agent that results in death of the microorganism. The MBC and MFC tests have been powerful methods to compare the germ-killing activity of several antimicrobial agents at once, often for screening purposes. In general, if the MBC/MFC is no more than four times the MIC, the antimicrobial agents are regarded as bactericidal/fungicidal. In some cases, the MBC/MFC of an antimicrobial agent is very close to its MIC. If the MBC/MFC of the tested agent against the tested microorganism is ≥ 32 times the MIC, it can be determined that the microorganism has developed resistance to the tested antimicrobial agent.

MIC and MBC/MFB evaluations are typically required in the following circumstances:

  • During the R&D phase of a product to determine appropriate antibacterial agent concentration required in the final product
  • As part of specific clinical scenarios to customize the treatment to treat only the causative bacterium
  • In support of a product tested as an investigational new drug. The FDA clearly specifies what microorganisms must be used to challenge the product in vitro
  • For a proof of concept in marketing purposes

Available Minimum Inhibitory Concentration (MIC) Services

  • Minimum Inhibitory Concentration (MIC)
  • Minimum Bactericidal/Fungicidal Concentration (MBC/MFC)

Read More About MIC Testing

PBL’s Sterility Assurance Booklet
Download the free booklet

Pacific BioLabs