Microbiological assay of vitamins MCQs With Answer

Microbiological assay of vitamins MCQs With Answer

Introduction: This quiz set is designed for M.Pharm students studying Biological Evaluation of Drug Therapy, focusing on microbiological assays used to determine vitamin potency. Microbiological assays measure the biological activity of vitamins by observing the growth response of selected microorganisms to different concentrations of a sample versus a standard. These methods are particularly valuable when chemical assays cannot distinguish biologically active forms or when high sensitivity is required. The following 20 MCQs cover principles, organisms commonly used, assay formats, validation criteria and practical factors affecting assay performance to reinforce understanding and exam preparedness.

Q1. What is the basic principle of a microbiological assay for vitamins?

• Measurement of vitamin oxidation by electrochemical sensors
• Growth response of a specific microorganism to varying vitamin concentrations
• Separation of vitamins by chromatography and quantitation by UV
• Direct chemical titration of the vitamin molecule

Correct Answer: Growth response of a specific microorganism to varying vitamin concentrations

Q2. Which microorganism is traditionally used for the microbiological assay of vitamin B12 (cyanocobalamin)?

• Lactobacillus casei
• Lactobacillus leichmannii
• Escherichia coli
• Saccharomyces cerevisiae

Correct Answer: Lactobacillus leichmannii

Q3. Which assay format measures turbidity (optical density) as the endpoint to quantify vitamin potency?

• Agar diffusion (plate) assay
• Turbidimetric (broth) assay
• Bioautography assay
• Colorimetric chemical assay

Correct Answer: Turbidimetric (broth) assay

Q4. In a well-designed microbiological assay, dose–response is typically linear when plotted as:

• Response versus square of concentration
• Response versus logarithm of concentration
• Log(response) versus concentration
• Response versus reciprocal of concentration

Correct Answer: Response versus logarithm of concentration

Q5. Which organism is commonly used for the microbiological assay of folic acid (vitamin B9)?

• Lactobacillus casei
• Pseudomonas aeruginosa
• Staphylococcus aureus
• Saccharomyces boulardii

Correct Answer: Lactobacillus casei

Q6. Which agar diffusion method is often employed in microbiological assays to measure growth promotion or inhibition on plates?

• Cylinder-plate method
• Chromatographic plate method
• Electrochemical diffusion method
• Direct fluorometric plate method

Correct Answer: Cylinder-plate method

Q7. What is the primary advantage of a microbiological assay over a purely chemical assay for vitamins?

• Lower equipment cost for all laboratories
• Ability to measure biologically active potency rather than just chemical concentration
• Shorter assay times for all vitamins
• Insensitivity to incubation conditions

Correct Answer: Ability to measure biologically active potency rather than just chemical concentration

Q8. Which of the following factors is least likely to significantly affect the outcome of a microbiological vitamin assay?

• Incubation temperature
• pH of the medium
• Inoculum size (initial cell density)
• Color of the laboratory walls

Correct Answer: Color of the laboratory walls

Q9. Which endpoint measurement is used in turbidimetric microbiological assays?

• Diameter of inhibition zone in mm
• Optical density (absorbance) at a specified wavelength
• Color change measured visually
• Mass of dry biomass after filtration

Correct Answer: Optical density (absorbance) at a specified wavelength

Q10. Why must culture media for microbiological assays be free from trace antibiotics or inhibitory contaminants?

• They increase the turbidity of the medium
• They can inhibit the test organism and falsely reduce the observed response
• They enhance growth and artificially inflate potency
• They change the pH but do not affect growth

Correct Answer: They can inhibit the test organism and falsely reduce the observed response

Q11. The biological activity of vitamins determined by microbiological assay is commonly expressed in which unit for comparability?

• Milliequivalents (mEq)
• International Units (IU)
• Parts per million (ppm)
• Molality (mol/kg)

Correct Answer: International Units (IU)

Q12. Which validation parameter assesses the ability of an assay to remain unaffected by small deliberate variations in method conditions?

• Specificity
• Ruggedness
• Robustness
• Accuracy

Correct Answer: Robustness

Q13. In agar diffusion microbiological assays, the zone diameter typically correlates best with which mathematical transformation of concentration?

• Square root of concentration
• Logarithm of concentration
• Reciprocal of concentration
• Exponential of concentration

Correct Answer: Logarithm of concentration

Q14. Which vitamin is commonly analyzed by microbiological assay because chemical methods may not reflect its complete biological activity?

• Vitamin C (ascorbic acid)
• Vitamin B12 (cyanocobalamin)
• Vitamin E (tocopherol)
• Vitamin K1 (phylloquinone)

Correct Answer: Vitamin B12 (cyanocobalamin)

Q15. How does deviation of medium pH from the optimum affect a microbiological vitamin assay?

• It has no effect on the assay outcome
• It may alter organism growth and thereby change the measured potency
• It only affects chemical assays, not microbiological ones
• It enhances vitamin stability uniformly

Correct Answer: It may alter organism growth and thereby change the measured potency

Q16. Which statistical approach is commonly used to test parallelism and linearity of dose–response curves in microbiological assay validation?

• Chi-square test
• Tukey’s post hoc test
• Analysis of variance (ANOVA)
• Kruskal-Wallis test

Correct Answer: Analysis of variance (ANOVA)

Q17. What does a microbiological bioassay measure directly?

• Chemical purity of the vitamin compound
• Biological activity or potency as manifested by a biological response
• Total organic carbon content
• Weight percentage of the active ingredient

Correct Answer: Biological activity or potency as manifested by a biological response

Q18. In a plate-count type microbiological assay, the quantitative result is most often reported as:

• Absorbance units at 600 nm
• Colony forming units (CFU)
• Zone inhibition area in mm²
• Dry weight of cells in mg

Correct Answer: Colony forming units (CFU)

Q19. During method validation, acceptable parallelism between the standard and sample dose–response lines is indicated by which outcome of the statistical test?

• A significant difference with p < 0.01
• A non-significant difference (p > 0.05)
• Identification of outliers in both sets
• Equal intercepts but different slopes

Correct Answer: A non-significant difference (p > 0.05)

Q20. Which practical step improves precision in microbiological vitamin assays?

• Varying inoculum size between replicates
• Using fresh, standardized inoculum and consistent incubation conditions
• Changing incubation temperature mid-assay
• Mixing different media formulations across replicates

Correct Answer: Using fresh, standardized inoculum and consistent incubation conditions

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