Minimum Inhibitory Concentration(MIC)|Minimum Bactericidal Concentration|Post Antibiotic Effect

Minimum Inhibitory Concentration(MIC)|Minimum Bactericidal Concentration|Post Antibiotic Effect

Lecture

The Minimum Inhibitory Concentration (MIC) is defined as the lowest concentration of an antimicrobial ingredient or agent that is bacteriostatic (prevents the visible growth of bacteria).

• MICs are used to evaluate the antimicrobial efficacy of various compounds by measuring the effect of decreasing concentrations of antibiotic/antiseptic over a defined period in terms of inhibition of microbial population growth.
• These evaluations can be quite useful during the R&D phase of a product to determine appropriate concentrations required in the final product, as the concentration of drug required to produce the effect is normally several hundred to thousands of times less than the concentration found in the finished dosage form.

The minimum bactericidal concentration (MBC) is the lowest concentration of an antibacterial agent required to kill a particular bacterium.

• It can be determined from broth dilution minimum inhibitory concentration (MIC) tests by subculturing to agar plates that do not contain the test agent.
• The MBC is identified by determining the lowest concentration of antibacterial agent that reduces the viability of the initial bacterial inoculum by ≥99.9%.
• The MBC is complementary to the MIC; whereas the MIC test demonstrates the lowest level of antimicrobial agent that inhibits growth, the MBC demonstrates the lowest level of antimicrobial agent that results in microbial death.
• This means that even if a particular MIC shows inhibition, plating the bacteria onto agar might still result in organism proliferation because the antimicrobial did not cause death.
• Antibacterial agents are usually regarded as bactericidal if the MBC is no more than four times the MIC.

The post antibiotic effect (PAE) is defined as persistent suppression of bacterial growth after a brief exposure (1 or 2 hours) of bacteria to an antibiotic even in the absence of host defense mechanisms.

• Theoretically, the ability of an antibiotic to induce a PAE is an attractive property of an antibiotic since antibiotic concentrations could fall below the MIC for the bacterium yet retain their effectiveness in their ability to suppress the growth.
• Therefore, an antibiotic with PAE would require less frequent administration and it could improve patient adherence with regard to pharmacotherapy