Pharma Interview Q and A Sep-17-21

September 17, 2021: Pharmaceutical Interview Questions and Answers

#ProcessOFGrowthPromotionTestForMicrobiologyCultureMedia #CalculationOfProductivityRatio #GPTAcceptanceCriterion #QuantitativeTechniquesOfGrowthPromotionTests #MilesMisraGPT #EcometricMethodofGPT

1. What is the process of Growth Promotion test of microbiology culture media? What should be the acceptance criteria?

1. Medium to be inoculated with a microorganisms <100 Colony Forming Units (CFU).

2. Use not less than five unique strains as recommended by the pharmacopoeias and two organisms from environment isolates on rotation basis (It should be within the five passages from the original reference culture seed lot).

3. Compare the growth on the medium with medium previously approved culture lot.

4. Acceptance is no more than a factor of 2 differences in productivity ratio calculations.

2. What is the calculation of productivity ratio and what is the acceptance criterion for agar media plate or solid media for growth promotion test?

Productivity ratio =

Mean of two test plates (cfu)/ Mean of two comparative control plates (cfu)

An acceptable productivity ratio should be (0.5 – 2.0). That is equivalent to a 50 – 200 % recovery.

3. What are the quantitative techniques of Growth Promotion Tests for Solid media?

Quantitative techniques of Growth Promotion Tests are of two types.

● Ecometric

● Miles – Misra (Drop Count)

4. Explain ecometric method of Growth Promotion Tests?

This technique is semi-quantitative variant of the streaking.

This technique is operator-dependent and has lower precision. However, it can be used to great effect with practice.

Following are the steps:

● A fresh suspension of the challenge organism is taken into a calibrated loop (One loopful of inoculm).

● Five streaks are streaked out into four quadrants onto the agar plate along with a final streak in the center of the plate.

● These plates are then incubated overnight for growth.

● The patterns of growth are interpreted to provide an Absolute Growth Index (AGI)

5. Explain Miles – Misra technique (the drop count technique) of Growth Promotion Tests?

This technique involves spreading droplets of known quantities (10 μL) of microbial suspensions.

The test plate is compared against control plate after incubation to verify number of colonies recovered.


The accuracy of the method is dependent on following factors:

● Dilution used

● Number of colony forming units (cfu) in the inoculum

● Volume of the inoculums

● Spreading technique

Scroll to Top