Question:
Turbidimetric assay measures
Turbidimetric assay measures
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Microbiological assays of antibiotics can be done in two main ways: the diffusion (cup-plate) method and the turbidimetric (tube) method. Understanding what each one actually measures is the key here.
Updated On: Jun 24, 2026
- Zone of inhibition
- Cell count
- Enzyme activity
- Optical density of microbial growth
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The Correct Option is D
Solution and Explanation
Concept:
Microbiological assays of antibiotics can be done in two main ways: the diffusion (cup-plate) method and the turbidimetric (tube) method. Understanding what each one actually measures is the key here.
Step 1: In the turbidimetric assay, the antibiotic is added to a liquid culture of test organisms. If the antibiotic inhibits growth, the broth stays clear; if it does not, the organisms multiply and the broth becomes cloudy (turbid). We measure this cloudiness as turbidity using a colorimeter or spectrophotometer.
Step 2: Turbidity is read as optical density (absorbance) of the microbial suspension — more growth means higher optical density. So the turbidimetric assay measures the optical density of microbial growth.
Step 3: The other choices belong elsewhere — the zone of inhibition is measured in the diffusion (cup-plate) method, while cell count and enzyme activity are separate determinations not used to read out this assay.
Answer: Option (4) — a turbidimetric assay measures the optical density of microbial growth. (4)
Microbiological assays of antibiotics can be done in two main ways: the diffusion (cup-plate) method and the turbidimetric (tube) method. Understanding what each one actually measures is the key here.
Step 1: In the turbidimetric assay, the antibiotic is added to a liquid culture of test organisms. If the antibiotic inhibits growth, the broth stays clear; if it does not, the organisms multiply and the broth becomes cloudy (turbid). We measure this cloudiness as turbidity using a colorimeter or spectrophotometer.
Step 2: Turbidity is read as optical density (absorbance) of the microbial suspension — more growth means higher optical density. So the turbidimetric assay measures the optical density of microbial growth.
Step 3: The other choices belong elsewhere — the zone of inhibition is measured in the diffusion (cup-plate) method, while cell count and enzyme activity are separate determinations not used to read out this assay.
Answer: Option (4) — a turbidimetric assay measures the optical density of microbial growth. (4)
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