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Determination of Minimum Inhibitory Concentration

determination minimum inhibitory concentration
determination minimum inhibitory concentration

1. Aim

To determine the minimum inhibitory concentration, or MIC, from a valid broth-dilution teaching dataset. The organism and drug identities are to be recorded from the assigned current monograph or approved college method in the student record from the assigned dataset. Enter tested concentrations and the calculated MIC in the student record.

2. Requirements

Instructor-supplied dilution-series image or dataset, labelled antimicrobial concentrations, growth and sterility controls, quality-control strain result, current CLSI M07 instructions, results sheet. Follow the approved method for medium, inoculum, dilution preparation, and incubation. Interpretation criteria are to be recorded from the assigned current monograph or approved college method in the student record against the current organism and drug-specific standard.

3. Theory

MIC is the lowest tested antimicrobial concentration that prevents visible growth under the specified test conditions. It is an in-vitro endpoint, not a patient dose. A doubling dilution series creates ordered concentrations; the first clear well after growing wells is a candidate MIC only when controls are valid and the well pattern is interpretable. A skipped well, contaminated sterility control, or absent growth control invalidates a simple read. A susceptibility category needs separate organism and drug-specific criteria.

4. Procedure

  1. Confirm the test identity, concentration units, dilution direction, and valid quality-control record.
  2. Read the growth control and sterility control before interpreting the test wells.
  3. Record visible growth for every concentration from lowest to highest without filling gaps by assumption.
  4. Locate the lowest tested concentration with no visible growth if the sequence and controls are valid.
  5. State MIC with units and any range or off-scale qualifier prescribed by the verified method.

5. Observation and calculation

Student record field Entry
Case or product Record here
Method Record here
Observation Record here
Inference Record here
Supervisor check Record here
Outcome Record here

Assumed values for practice only: assumed concentrations are 1, 2, 4, and 8 mg/L; assumed growth is present at 1 and 2 mg/L and absent at 4 and 8 mg/L, with assumed valid controls. The illustrative MIC is 4 mg/L. Every input and the 4 mg/L output are assumed, not an actual result or a laboratory dilution instruction.

6. Output or final result

Report the lowest inhibitory tested concentration only when the controls and pattern support it. Actual MIC: Record here.

Teaching-lab safety: Use a supplied dataset or an instructor-approved low-risk strain in a supervised laboratory. Do not handle clinical isolates or use the class result for treatment decisions.

This page is a supervised-activity guide; it does not report a completed case.

7. Sources

← Sterility Testing for Powders and LiquidsMicrobiological Assay of Antibiotics by Cup Plate Method →

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Theory notes: Pharmaceutical Microbiology