John Hay
John Hay Biomedical
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Genetics of Disease (Medical Interventions)
Unit 1: Unit 1.2 Antibiotic TreatmentMI 1.2Culturing

Interpret Zone-of-Inhibition MIC

Use culture and antibiotic evidence to interpret zone-of-inhibition / mic.

Builds on (2 levels back)inferred · high confidence
  • Aseptic culture technique: Culture results need uncontaminated samples.
  • Antibiotic selection pressure: Drug exposure can favor resistant bacteria.

Prerequisites are inferred: pending teacher review.

Re-learn the skill with worked practice and clear examples.

Use culture and antibiotic evidence to interpret zone-of-inhibition / mic.

Step 1: Learn the key
Compare growth, zone size, or MIC to the [blank] before choosing an antibiotic or explaining [blank].
AntibioticZoneInterpretation rule
A22 mmlarger zone = more inhibition
B8 mmless inhibition
C0 mmno inhibition
Zone of inhibition table
Step 2: Use the model
Read the figure, table, control, range, or protocol before choosing an answer.
Step 3: Name the limit
Say what the evidence can support and what it cannot prove yet.
Practice

Use the culture figure/table. Which antibiotic appears most effective in the shown test?

Reviewed
AntibioticZoneInterpretation rule
A22 mmlarger zone = more inhibition
B8 mmless inhibition
C0 mmno inhibition
Zone of inhibition table
  1. A.The one with the largest zone or lowest MIC
  2. B.The one with no clear zone
  3. C.The one listed last
  4. D.The one with the longest name
Show the worked solution ▾

Answer: A. The one with the largest zone or lowest MIC

  1. Step 1: Use effectiveness rule: Large zone or low MIC means growth was stopped at lower/better conditions.
  2. Step 2: Compare results: Choose by the rule, not order or name.

Why it's right: The result-based choice is most effective in the test.

Why the others miss:
  • B: No clear zone means poor inhibition.
  • C: List order is not evidence.
  • D: Name length is irrelevant.

Aligned to Culturing · reading level ~grade 9

Where you'd see this
  • In Unit 1.2 Antibiotic Treatment, this skill turns class evidence into a result another person can check.
Careers that use this
Microbiologist: Uses interpret zone-of-inhibition / mic to make a decision from evidence without overclaiming.
Video library
Watch: Interpret Zone-of-Inhibition MIC
Disc Diffusion (Kirby-Bauer) Antimicrobial Susceptibility Testing
TheRubinLab · ~6 min
Guided notes

Fill these in as you work through the lesson.

Big idea: Use culture and antibiotic evidence to interpret zone-of-inhibition / mic.
Key terms: write the meaning
  • Bacteriostatic (stops bacterial growth):  
  • Bactericidal (kills bacteria):  
  • MIC (lowest drug level that stops visible growth):  
  • Resistance (bacteria survive a treatment):  
The rule

Compare growth, zone size, or MIC to the   before choosing an antibiotic or explaining  .

Check yourself
  1. Is growth present? 
  2. Which drug has the lowest MIC or largest zone? 
  3. How could resistance spread? 
Work one example

Use the culture result to practice interpret zone-of-inhibition / mic and name one stewardship concern.