Question

Can the reults if an MIC test be used to determine whether an anitbiotic is bactericidal or bacteriastatic? If not, set up an experimental procedure to determine whether the effect is bactericidial or bacteriastatic.

Answer 1

MINIMUM INHIBITORY CONCENTRATION TEST

The minimum inhibitory concentration (MIC) test is the chemical lowest concentration that inhibits visible bacterium growth. This is measure as difference to the minimum bactericidal concentration or MBC that is the concentration resulting in death of microbes so it is also defined by the failure to re-culture bacteria. So it can say that if closer the MIC to the MBC, than the compound is more bactericidal.

THE MINIMUM INHIBITORY CONCENTRATION TEST performance in laboratory (MIC TEST):

• A single microorganism’s pure culture was developed in Mueller-Hinton broth or in other broth as suitable.
• Then the culture was standardized by used standard microbiological techniques to had a concentration which is exact close 1 million cells/ml. if the microbial culture is more standard , the test results is also the more reproducible.
• After that the antimicrobial agent was diluted many times, generally 1:1, with a sterile diluent like typically Mueller-Hinton broth.
• After the dilution of antimicrobial agent, added a volume of the standardized inoculum same to the volume of diluted antimicrobial agent, to all dilution vessel, so getting the microbial concentration to around 500,000 cells/ml.
• The serially diluted antimicrobial agent after inoculation was incubated at a suitable temperature for the test organism for a pre-set period, generally for 18 hours. If the incubation period is more consistent, the test results is also more reproducible.
• The series of dilution vessels was observed after incubation, for determining the microbial growth, generally shown by turbidity or a pellet of microorganisms in the bottom of the vessel.
• In the dilution series, the last tube that did not show growth relates with the antimicrobial agent’s minimum inhibitory concentration or MIC.

STRENGTHS OF THE MINIMUM INHIBITORY CONCENTRATION TEST (MIC TEST):

• Relatively the MIC test is direct and easy to prepare, which naturally increases reproducibility.
• This test could be done on a very minor scale without consuming large quantity of antimicrobial agent. This is significant for the experiment of antimicrobial, like antimicrobial peptides which was biologically synthesized.
• The MIC test is easy to perform to test the antimicrobial characteristics of a formulation through different parameters, like surfactant blends or cross microbial species.
• Because minute preparation is need for the MIC testing, test turnaround time could be kept short.

WEAKNESSES OF THE MINIMUM INHIBITORY CONCENTRATION TEST or MIC TEST :

• Minor differences in the MIC test parameter may had main influences on the seeming MIC. Like if long incubation would make the MIC appear to be more, and lower inoculum concentration would make the MIC perform to be minor.
• from MIC study results must be evaluated in the appropriate context.
• MIC test is especially suitable if liquid antimicrobial agent would be used fot inhibit the growth of microorganism in specific context.