The main difference between MIC and MBC is that MIC is the minimum inhibitory concentration or the lowest concentration of antimicrobial drug that will inhibit the visible growth of bacteria after overnight incubation, whereas MBC is the minimal bactericidal concentration or the lowest concentration of antibacterial agent required to kill a particular bacterium.
MIC and MBC are two parameters that determine the activity of a particular drug on certain species of bacteria.
Key Areas Covered
1. What is MIC (Minimal Inhibitory Concentration)
– Definition, Facts, Importance
2. What is MBC (Minimum Bactericidal Concentration)
– Definition, Facts, Importance
3. Similarities Between MIC and MBC
– Outline of Common Features
4. Difference Between MIC and MBC
– Comparison of Key Differences
Key Terms
MBC, MIC, Minimum Bactericidal Concentration, Minimal Inhibitory Concentration
What is MIC
MIC, or minimal inhibitory concentration, is the lowest concentration of the antimicrobial drug that inhibits bacteria’s visible growth after overnight incubation. For the determination of MIC, a broth dilution assay is used. This assay uses different broth, media, and bacteria concentrations in 96 wells plates. Moreover, an antimicrobial drug dilution is two-fold, from 50 to 2.44×10−2 µg/ml. The drug is dissolved in both water and THF. M. avium is the type of bacteria used in the assay, and the approximate cell density is r 1×108 CFU/ml. On the other hand, Middlebrook 7H9 broth is the type of medium used in the assay. The incubation period is 35 °C for one week. Significantly, MIC is the concentration of the drug in the first well, which contains a clear solution with no turbidity resulting from bacterial growth.
Figure 1: MIC Assay
Furthermore, MIC determines the concentration of the antimicrobial agent that can inhibit the growth of microorganisms such as bacteria and fungi. Additionally, in laboratories, MIC is important in grading microorganisms as susceptible (S), intermediate (I), and resistant (R) to a particular antimicrobial drug. It is helpful for physicians to determine and prescribe suitable antimicrobial medications for a specific microorganism. Also, MIC provides the antimicrobial potency of a particular compound. However, the lower the MIC, the antimicrobial compound is more potent.
What is MBC
MBC, or minimum bactericidal concentration, is the lowest antimicrobial concentration required to kill a particular microorganism. Agar plate assay is essential for the determination of MBC. Bacterial suspension and diluted drug are inoculated in a broth well plate using a cathedra replicator with a 3 mm pin. First, the cathedra replicator is sterilized for 1 minute on flame. Middlebrook 7H10 Agar is the type of agar used in this experiment. Also, 5 µg of the bacterial suspension of M. avium is inoculated on to agar plate. Additionally, the antimicrobial drug is added in varying concentrations to the wells. The incubation period is 35 °C for one week. Here, the MBC is the concentration of the first clear area on the agar plate.
Figure 2: Etest, Alternative Method for MIC
Moreover, MBC is the lowest concentration of drug that kills microorganisms. Therefore, these types of antibacterial agents are bactericidal.
Similarities Between MIC and MBC
- MIC and MBC are two parameters used to determine the activity of a particular drug on bacterial growth.
- Both dilutions and agar plates are used in testing the drug concentrations.
- They are incubated at 35 °C for one week.
- M. avium is the type of microorganism used in each test.
Difference Between MIC and MBC
Definition
MIC, or minimum inhibitory concentration, refers to the lowest concentration of a chemical, usually a drug, which prevents visible in vitro growth of bacteria or fungi. In contrast, MBC, or minimal bactericidal concentration, refers to the lowest concentration of an antibacterial agent required to kill a bacterium over a fixed, somewhat extended period, such as 18 hours or 24 hours, under specific conditions.
Type
MIC determines the concentration of bacteriostatic drugs, while MBC determines the concentration of bactericidal drugs.
Type of Test
For MIC, broth dilution assay is used, while for MBC, agar plate assay is used.
Results
MIC is the concentration of the first well with no turbidity taken as the drug concentration, while MBC is the concentration of the first clear area taken as the drug concentration.
Media
Middlebrook 7H9 broth is the medium in MIC, while Middlebrook 7H10 Agar is the medium in MBC.
Importance
MIC is important for grading microorganisms as susceptible (S), intermediate (I), and resistant (R) to a particular antimicrobial drug, while MBC is important for the determination of bactericidal drugs.
Conclusion
In brief, MIC and MBC are two parameters to determine the activity of a particular drug against microorganisms. MIC, or minimum inhibitory concentration, is the lowest concentration of the drug that prevents the visible growth of bacteria. Broth dilution assay is used in the determination of MIC. It determines the concentration of the bacteriostatic drugs. Also, MIC is the concentration of the first well with no turbidity. Additionally, Middlebrook 7H9 broth is the medium in the MIC test. On the other hand, MBC, or minimal bactericidal concentration, is the lowest drug concentration that kills bacteria over a fixed period. It determines the concentration of the bactericidal drugs. However, the agar plate method is used to determine MBC, and the medium used is the Middlebrook 7H10 Agar. Therefore, the main difference between MIC and MBC is the type of drugs tested.
References:
- MBC. MBC – an overview | ScienceDirect Topics. (n.d.).
Image Courtesy:
- “Minimum Inhibitory Concentration” By Jenay DeCaussin – Own work (CC-BY SA 4.0) via Commons Wikimedia
- “Etest Vancomycin S aureus” By Microrao – Own Work (Public Domain) via Commons Wikimedia
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