MIC.pptx

MIC broader outlook

1. MINIMUM INHIBITORY CONCENTRATION T he  minimum inhibitory concentration  ( MIC ) is the lowest concentration of a chemical, usually a drug, which prevents visible  growth  of a bacterium or bacteria. MIC depends on the microorganism. Minimal inhibitory concentration (MIC) defines in vitro levels of susceptibility or resistance of specific bacterial strains to applied antibiotic. Reliable assessment of MIC has a significant impact on the choice of a therapeutic strategy, which affects efficiency of an infection therapy.

2. Understanding key terms Susceptible- Microorganism is inhibited by concentration of antimicrobial agent Resistant – Microorganisms is resistant to concentration of antimicrobial agent Bacteriostatic - A drug that prevents bacterial growth and reproduction but does not necessarily kill them. When it is removed from the environment the bacteria start growing again.

3. MINIMUM INHIBITORY CONCENTRATION The MIC is determined by preparing solutions of the chemical  in vitro  at increasing concentrations Incubating the solutions with separate batches of cultured bacteria, M easuring the results using  agar dilution  or  broth microdilution . Results have been graded into susceptible (often called sensitive),increased exposure, or resistant to a particular antimicrobial by using a breakpoint. Regulatory Agencies:   Clinical and Laboratory Standards Institute  (CLSI) British Society for antimicrobialChemotherapy  (BSAC) European Committee on Antimicrobial Susceptibility Testing (EUCAST) .

4. Broth dilution method The broth/tube dilution test is the standard method for determining levels of microbial resistance to an antimicrobial agent. Serial dilutions of the test agent are made in a liquid microbial growth medium inoculated with a standardized number of organisms and incubated for a prescribed time . At the end of the incubation period (generally 18-24 hours), the tubes are visually examined for turbidity

5. Relationship between MIC and Zone of Inhibition The MIC and the zone diameter of inhibition are inversely correlated. The more susceptible the microorganism is to the antimicrobial agent, the lower the MIC and the larger the zone of inhibition. Conversely, the more resistant the microorganism, the higher the MIC and the smaller the zone of inhibition . MIC is determined only in specific clinical scenarios under the instruction of a Microbiologist, e.g.,  infective endocarditis.  MIC gives valuable information, which will help to customize the treatment to direct only the causative bacterium.

6. Interpretation of results Broth dilution susceptibility test (MIC 6.25μg/mL) E.g. in the image shown above, the breakpoint of growth inhibition lies between 6.25 (no turbidity is seen) and 3.12 μg /mL (turbidity is still appearing) of antimicrobial agents. However, by convention, the MIC is interpreted as the concentration of the antimicrobial agent contained in the first tube in the series that inhibits visible growth. Therefore, in this example, the MIC is 6.25 μg /mL REPORTING MIC RESULTS Laboratories have to report the interpretive category (susceptible, susceptible-dose-dependent, intermediate, or resistant) to the physician with or without MIC value . 

7. MIC, MBC   MIC is the lowest concentration of an antibacterial agent necessary to inhibit visible growth. M inimum bactericidal concentration (MBC)   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 a specific set of conditions.

8. microbroth dilution method Microbroth Dilution Method : To identify the lowest concentration required for a given antibiotic to inhibit bacterial growth, an identical amount of bacteria is introduced into wells of liquid media containing progressively lower concentrations of the drug. (Here, the dilution series of the drug is set up from left to right: for example, well E1 might contain 100 units of drug; E2, 50 units; E3, 25 units; E4, 12.5 units; etc.). Because bacterial growth made the media in well E5 cloudy and the media in well E4 is indistinguishable from clear media, this indicates that the minimum inhibitory concentration is between the drug concentrations in wells E4 and E5.

9. RESULTS

10. Significance and Applications An MIC is generally regarded as the most basic laboratory measurement of the activity of an antimicrobial agent against an organism. Because a lower MIC value indicates that less of the drug is required in order to inhibit growth of the organism, drugs with lower MIC scores are more effective antimicrobial agents. Currently , there are a few web-based, freely accessible MIC databases. MIC scores are important in diagnostic laboratories to confirm resistance of microorganisms to an antimicrobial agent and also to monitor the activity of new antimicrobial agents. Clinicians use MIC scores to choose which antibiotics to administer to patients with specific infections and to identify an effective dose of antibiotic. This is important because populations of bacteria exposed to an insufficient concentration of a particular drug or to a broad-spectrum antibiotic (one designed to inhibit many strains of bacteria) can evolve resistance to these drugs. Therefore , MIC scores aid in improving outcomes for patients and preventing evolution of drug-resistant microbial strains.

11. REFERENCES https://www.ncbi.nlm.nih.gov https://en.wikipedia.org https://pubmed.ncbi.nlm.nih.gov https://microchemlab.com/test/minimum-inhibitory-concentration-test-mic/