Question

The following tests can be applied to determine Minimum Inhibitory Concentration (MIC) values against an isolated bacterium
A. Kirby Bauer method
B. Broth Dilution method
C. E - test
D. Miles Mishra Technique
Choose the correct answer from the options given below:

• A. A and B only
• B. A and D only
• C. B and C only
• D. C and D only

Hint:

Antimicrobial Testing:
Quantitative MIC Determination = Broth Dilution Method & E-test (Epsilometer test).
Qualitative Disc Diffusion = Kirby-Bauer Method.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Antimicrobial susceptibility testing distinguishes qualitative categorical disc diffusion methods from quantitative MIC dilution and gradient diffusion assays.
Key Formula or Approach:
\[ \text{MIC} = \text{Lowest concentration of antimicrobial (}\mu\text{g/mL) that prevents visible bacterial growth} \]

Step 2: Detailed Explanation:
Evaluating microbiological antimicrobial testing methods:
1. Broth Dilution Method (Macro/Micro-dilution) (B): The reference gold standard quantitative method where serial two-fold dilutions of antimicrobial agent yield the exact MIC value in $\mu\text{g/mL$}.
2. E-test (Epsilometer Test) (C): A predefined continuous exponential antimicrobial gradient strip placed on an agar plate; where the symmetrical elliptical inhibition halo intersects the strip gives direct quantitative MIC readout.
3. Kirby-Bauer Method (A): Qualitative agar disc diffusion measuring zone diameter of inhibition (categorized as Sensitive, Intermediate, Resistant), not direct MIC.
4. Miles-Misra Method (D): Quantitative surface drop bacterial colony counting method.
Thus, B and C only directly determine MIC values.

Step 3: Final Answer:
Hence, the tests applied to determine MIC values are B and C only, corresponding to option (C).